Treatment of Acid Tars by Encapsulation to Reduce the Effects of

Pollution on the Environment

MIHAELA TITA1, DANIEL TITA1, ION ONUTU1, TIMUR CHIS2, LUCIAN ION TARNU3

1Oil, Petrochemical and Environmental Engineering Department,

Oil and Gas University,

Blv. Bucuresti, nr.39, Ploiesti,

ROMANIA

2Oil and Gas Engineering Department,

Oil and Gas University,

Blv. Bucuresti, nr.39, Ploiesti,

ROMANIA

3Managing and Industrial Engineering Department,

Lucian Blaga University,

Victoriei Blv, nr.10, Sibiu,

ROMANIA

Abstract: - Some synthesis processes obtain Acid tars after treating the refining products with sulfuric acid.

They are highly toxic to the environment, occupying important storage spaces. Following the closure of the

refineries in Romania, large quantities of acid tars were abandoned in oil residue tanks. Currently, activities are

being carried out to inventory and dispose of them. Incineration is the only possibility to treat these wastes,

which release dangerous substances into the air (CO2, SO2). That is precisely why we tried to find solutions to

treat these wastes by encapsulating them with various additives, the best solution being their physical alteration

through encapsulation and stabilization in situ. The results obtained from the treatment of some acid tars taken

from Romania, with additives consisting of cement, sand, calcium oxide, sodium hydroxide, bentonite, and

emulsifier, are presented, the created recipes being used to treat 80 collected tar samples. The effects of these

recipes on the primary pollutants are also analyzed (metal content, total hydrocarbons in oil, the number of

acids, cyanides, chlorides, and sulfates).

Key-Words: acid tars, additives, pollution, oil waste, encapsulation, disposal, physical alteration.

Received: March 9, 2023. Revised: November 23, 2023. Accepted: December 2, 2023. Published: December 31, 2023.

1 Introduction

More than 80% of petroleum waste generated in

refineries is reused, regenerated, or recycled, and the

remaining 20% is disposed of by an acceptable

method, [1].

Oil waste, pollutes the environment and

occupies important areas of arable land and

constitutes, at the same time, an essential loss of

materials, grafting in this way the expenses of the

refinery, [2].

In these conditions, knowing the qualitative

limitations related to the total content of

hydrocarbons (TPH) and heavy metals of these

residual materials, the analysis methods were

established and discussed, later correlated with the

conditioning/treatment/bioremediation options (or

combined) for the preparation petroleum waste for

recovery or disposal, [3].

Wastes are generated throughout the petroleum

industry that include drilling fluids, hydrocarbon-

containing wastewater, oil effluent, treatment plant

sludge, tank bottom sludge, acid tars, spent

catalysts, bleaching earth, etc., [4]

At the refinery level, the amounts of residual

solid materials are within the limits of 3 to 5 kg/ton

of crude oil processed, mentioning that over 80% of

these residues are highly polluting because they may

contain toxic organic substances and heavy metals.

For any member state of the European Union,

therefore, also for Romania, the problem of

eliminating oil waste and the investigation and

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1329

Volume 19, 2023

remediation of lands historically contaminated with

such compounds is a priority.

According to the national inventory of

potentially contaminated sites for 165 years of crude

oil refining, in 2004, there were 1183 potentially

contaminated sites in Romania, of which 861 were

potentially contaminated sites from the oil industry.

Up to this moment, an area of 1,054,549 square

meters has been decontaminated, of which 377 oil

wells and 39 mud pits represent the equivalent of

84% of the total recorded at the national level, [5].

Tars are a sludge pollution refinery and are

liquid or semi-solid residues with mixed

composition resulting from the carbonization of

organic materials from a high-temperature process,

[6].

These industrial wastes come from the refining

of oils by adding sulfuric acid, thus containing

sulfonated organic compounds.

They were obtained for the first time at the end

of the 19th century, following the manufacture of

distilled oils, motor oils, and other types of oils, by

refining with concentrated sulfuric acid or with

oleum, [7].

At the same time, acid tars are the result of the

refining of special oils, such as transformer oil,

hydraulic oil, medicinal oil, and cosmetic oil, and

the production of flotation reagents and petroleum

additives, individual sulfonation of some

hydrocarbons and some petroleum fractions.

They are also obtained due to the alkylation of

isobutene with olefins, a process necessary for the

manufacture of a valuable octane component, and

by treating some aromatic compounds with oleum,

[8]. In England, removing impurities such as lead,

zinc, and manganese from used lubricating oils

using sulfuric acid resulted in acid tar of much more

variable composition than benzene refining, [9].

In some processes of treating flotation reagents,

a white oil is also obtained with a composition

dependent on the nature of the oil, the contaminants

it contains, and the amount of acid used, [10].

In the process of formation of acid tars, the

following stages are identified, [11]:

A. acid tars appear emulsified in the first phase,

with much less stability.

Afterward, the separation of an upper phase formed

by a lighter emulsion occurs, in which the

continuous phase is the petroleum product, and the

dispersed phase is sulfuric acid and water.

A thin film is formed between the two phases, made

of sulfonic acids;

B. In the second stage, sulfuric acid, water, and

low molecular weight sulfonates form a cloudy

gray-black solution containing sulfates of nitrogen

compounds;

C. Over time, the upper layer of acid tars is

washed away with rainwater, diluting the existing

sulfuric acid. Also, the organic mass begins to

oxidize due to the presence of oxygen in the

atmosphere and the heating of the tar (which works

as a black body and absorbs solar energy, reaching

temperatures of 80 - 95ºC);

D. During hot oxidation, resinous, asphalt genic,

and carbide compounds are obtained, the tar

maturing and becoming a solid mass. In this stage,

hydrogen sulfide releases ammonia, and sulfur

oxides into the atmosphere.

For aged tars, kept for a long time in storage pits

(petroleum residue storage pits) or observing the

following transformations:

A. In the first stage, the formation of a layer of

organic mass similar to bitumen, which can have a

softening point of up to 60ºC, was found on the

surface. This bituminous layer has a relatively low

mineral acidity, with a composition of heavy

sulfonic acids, heavy naphthenic-aromatic acids and

resins, asphaltenes, carbides and carbenes, chemical

products formed by polycondensation and

polymerization. The presence of some metals

(existing in crude oil) was also found.

In this layer, free hydrocarbons are only present

in a tiny proportion;

B. The lower layer is formed in acidulated water,

with dissolved compounds such as metallic sulfates

and sulfides of essential compounds from petroleum

products, [12].

These transformations of acid tars have as their

purpose the formation of thick, viscous tars that do

not separate easily and that have the property of

quickly dissolving oxygen and other strongly polar

components, which over time lead to

polymerization-polycondensation reactions with the

appearance of macromolecular compounds such as

resins and asphaltenes.

Thus, the tars take on the appearance of bitumen

that solidifies at the interface with the environment

and hardens over time.

The range of production processes that generate

tars, as well as the variations in the properties of

intermediate and final compounds, make the

physicochemical properties of acid tars vary

significantly from one batch of petroleum products

to another and even within the same batch, [13].

The presence of acid tars on a specific site/battle

can have the following characteristics and ways of

manifestation:

- Black or dark brown spots, signs of tar leaks or

unvegetated areas;

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1330

Volume 19, 2023

- Degraded surface tars;

-Gaps/depressions;

-Clay/gravel/sand pits;

-Grouped areas;

-Areas with smells;

-Areas with previous fires.

Depending on the environmental conditions, its

origin, and composition, the tar will have various

external forms, [14].

The most common form is friable tar, usually

observed on thin or isolated tar bodies that can lose

their water and content of volatile organic

compounds without being replenished from the bulk

tar mass. This form of tar can produce dust-sized

particles that are vulnerable to the wind blowing and

thus migrating off-site.

In conclusion, acid tars are secondary products

from refining petroleum fractions, being complex

organic and inorganic mixtures with unique physical

properties.

2 Possibilities of Conditioning,

Treatment and Processing of Acid

Tars. History and Trends

Acid tars cause environmental pollution, occupy

important areas of arable land, and constitute an

essential loss of valuable minerals, grafting the

expenses of the refinery in this way.

That is why, since their formation, the

valorization of such wastes has been attempted.

Still, the complexity of their composition led to

the definition of various treatment techniques

suitable for the resulting waste.

Processing of acid tars has also been attempted,

yielding commercial products such as surfactants,

H2SO4 and colloidal sulfur, desulphurized light

liquid hydrocarbons, coke, and activated carbon,

fuel for boilers and furnaces, pitch, asphalt and

asphalt binders, compositions thermal insulation and

anti-rust mastics, commercial ammonium sulfate,

gypsum and cement obtained from deacidified

washing water with calcium oxide or hydroxide and

a mixture of acid tars with peat as a fuel with a high

calorific value.

However, during the treatment of acid tars, only

the top layer, which is easy to recover and process,

is usually used.

From the publications in circulation, it follows

that, over time, various possibilities of processing /

disposing of acid tars have been tried, briefly

described in what follows, [15].

2.1 Neutralization of acid tars

Neutralization can be achieved by applying

quicklime (calcium oxide) directly to the acid tar, in

situ, this being possible where the tar is located, in

the battle, at a shallow depth.

Alternatively, the process can be carried out ex-

situ, either in layers or in specially designed

installations. Due to the impossibility of achieving a

homogeneous mixture of calcium oxide and acid tar,

neutralization becomes a cumbersome process. It is

mainly undertaken as an intermediate step before

the final disposal of petroleum waste. During the

neutralization experiments, mixtures with different

intensities/degrees were performed. Thus, the tars

were mixed with earth to give a crispy, crumbly

texture suitable for neutralization. Even

contaminated soils from the site or from other sites

that could be used for this purpose were used, the

proportions achieved being 50:50 soil to tar.

Neutralization involves mixing the tar-soil

mixture with lime (up to 30% lime), and the

resulting neutralized tar could be stored before the

current European environmental protection

legislation.

As an option, the single application of acid tar

neutralization has become more and more difficult

because there are fewer suitable and available

landfills to accept this waste, the cost being over

200 Euro/ton.

2.2 Incineration of Acid Tars

Burning, as such, is applied to types of tars that do

not lend themselves to other processes or if the

small volume of tars makes other processes

uneconomical. In general, by burning, the volume of

residues is reduced by almost 85%, and for storing

the ash resulting from the burning of one ton of

residue, an area of only 0.1m² is required.

Viscous and semi-solid tars could be burned in

hearths with mobile feeding grates mixed with coal

or spent absorbent earth, the process being disturbed

by:

a. The appearance of corrosion at the burners, pipe

screens, and ovens' masonry;

b. Pollution of the atmosphere with gases containing

sulfur dioxide and trioxide.

2.3 Thermal Decomposition

The thermal decomposition of acidic tars

containing water is one of the oldest processes.

Depending on the types of tars, fluid or semi-fluid

residues and diluted sulfuric acid (30 - 40%) can be

obtained, with a content of unstable organic

compounds corresponding to 1.5 - 4% carbon,

compared to pure sulfuric acid.

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1331

Volume 19, 2023

In principle, the thermal decomposition takes

place at temperatures of 260 - 650ºC, involving the

reduction of free sulfuric acid to sulfur dioxide and

water, with the help of the hydrogen contained in

the organic substance from the tars.

At the same time, the cracking of the organic

substance takes place, resulting in light and

complex, volatile hydrocarbons and coke with a 7-

8% sulfur content.

Generally, tars with a sulfuric acid content of

about 50% are suitable as raw materials.

Thermal decomposition at high temperatures

was also used in practice, which is achieved by

completely burning tars to sulfur dioxide, carbon

dioxide, and water in cylindrical hearths where

ordinary fuel is also burned to maintain the

temperature at approximately 1000 - 1200ºC.

The heat is recovered partly by preheating the

combustion air and partly by the method applicable

for tars with a sulfuric acid content of over 75%.

2.4 Recovery of Sulfonic Acids

The organic substance in the tars may contain

recoverable sulfonic acids found in the solution in

the petroleum fraction and in the acid tars.

Considering the particular interest of the

industry in sulfonic acids and sulfonates, many

attempts have been made to recover them.

In the 80s, the possibility of obtaining coke

through the thermal decomposition of tars and

activated carbon used in adsorption cartridges from

gas masks was studied.

At the beginning of the second decade of the

last century, acid tars were neutralized with calcium

oxide or sodium hydroxide, and two organic masses

called NaDOS and CaDOS were obtained, which

were used to cover communal roads, [16].

Next, after the 60s of the last century, the acid

tar hydrolysis process was developed.

Another direction was using the acid tars from

the battles to manufacture bitumen and obtain heavy

fire fuels.

Modern technologies for the elimination of acid

tars, applicable to other petroleum wastes, are the

following, [17]:

- Pyrolysis at high temperatures (800–1200ºC)

producing H2SO4, heat, coke with high sulfur

content and activated carbon;

- Decomposition at low temperatures in the range of

150–350 ºC, followed by the production of bitumen;

- Hydrolysis with water or steam producing diluted

H2SO4 and combustible components;

-Neutralization with various agents such as

surfactants.

A reasonably advanced study, but not applied in

practice, was the one in which acid tars would have

been introduced into uranium mines to obtain rock

specific to the uranium deposit, [18].

The non-application was due, on the one hand,

to the difficulty of transporting the acid tars and, on

the other hand, to the closing of the mine in the later

phase. The problem of the processing/elimination of

acid tars is always current, and countries with highly

developed industries and clear legislation have

almost completely solved this problem.

3 Experimental Strategies

The environmental impact analysis of acid tars was

carried out through the following research stages,

[19]:

a. Documentary study from specialized literature

regarding petroleum residues/waste that can

contaminate the soil, physical and chemical

properties of the various categories of residual

materials that can influence the quality of the soil,

concerning current national and global methods for

the evaluation of petroleum hydrocarbons from soil

and legislative basis at the EU level and in

Romania;

b. Field study carried out during three years of

investigations in different areas polluted with crude

oil and petroleum residues/wastes, areas related to

Prahova refineries. A representative battle was taken

from these areas/battles, and more than 80 soil

samples were taken and analyzed in different stages

of the experimental studies.

c. Preliminary or detailed experimental studies

regarding the characterization and evaluation of

options for identification, analysis, treatment, and

possible valorization of some petroleum

residues/wastes, [20].

d. The laboratory studies for samples of oil

residues/waste taken from the sites where this waste

is stored included a series of complex and

complementary analyses to establish the

composition, physical and chemical properties that

can influence their behavior towards the storage

environment, data that provide the information

necessary for further processing/elimination, [21].

e. Study of statistical processing of experimental

data by using artificial intelligence and Data Science

to predict the properties of acid tars from battles and

the associated leachate. The Study will follow the

initial data processing, selecting the appropriate

modeling algorithm, and calculating its estimation

accuracy, [22].

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1332

Volume 19, 2023

To estimate the properties of new acid tar

samples without testing them, we have created a

computer tool that helps the user in this regard.

It was written using the Python programming

language, version 3.9.7, and the PyCharm

Community Edition programming environment,

version 2021.2.3.

They are free and can be downloaded from the

manufacturers' websites, [11].

The computer tool created uses mathematical

modeling and data science techniques to estimate

the following nine properties of acid tars sampled

from the GA battle:

-initial pH of the acid tar sample;

- The THP content of the acid tar;

-The initial concentration of lead in the acid tar

(mg/kg);

-Initial cadmium concentration (mg/kg);

-Initial concentration of copper (mg/kg);

- Initial concentration of chromium (mg/kg);

- The concentration of nickel in the acid tar

(mg/kg);

-The initial concentration of arsenic in acid tar

(mg/kg);

-The initial concentration of cyanides (mg/kg).

The nine properties presented above form the

independent variables (or predictor variables), and

the sampling depth is the dependent variable (or

response variable).

The following quantities are used as predictor

variables:

-X and Y coordinates of the points from which the

soil samples were extracted (stereographic

projection 70 is used as a representation system for

these coordinates);

-The depth from which the acid tar samples were

extracted (cm). These samples were taken from

either the 0.3 or 0.5 m depth.

The working algorithm of the developed program

has the following steps:

-Loading the raw data from the Excel file;

-Determining predictor variables (input data) and

response variables (output data) and selecting them

from the uploaded data;

-Dividing processed data into training data and

test data;

- Selection of the appropriate mathematical

model for the available data;

- Application of the mathematical model selected

in the previous step;

-Testing the estimation accuracy of the chosen

mathematical model.

Within the developed program, cross-validation

was applied to the forest of decision trees, resulting

in prediction equations of the form:

𝑦 = 𝑎0+ 𝑎1𝑥1+ ⋯ + 𝑎𝑛𝑥𝑛+ 𝜀 (1)

Where y represents the dependent variable (or

response variable), and 𝑥𝑖 represents the

independent variables (or explanatory variables).

The coefficients 𝑎𝑖 are calculated by the linear

regression algorithm so that the sum of squared

errors is minimal.

Among them, the coefficient 𝑎0 is constant and

is called the intercept.

The variable 𝜀 holds the approximation errors of

the model.

4 Materials and Methods

The optimal application of the processing, recovery,

or treatment/disposal methods of petroleum

residues/waste requires a thorough knowledge of

their chemical composition.

The potential valorization or correct disposal of

petroleum waste, especially those in the acid tars, in

conditions of proper preservation of the physical

environmental factors (air, water, and soil), is based

on applying a research methodology that includes

methods and equipment suitable analysis.

The characterization of waste and oil residues,

but also the final treated products, was achieved by

determining the following key indicators: pH, THP

content, metals, chlorides, Dissolved Organic

Carbon (COD), Sulphates, Total Dissolved Solids

(TDS), Carbon Total Organic (TOC).

According to Ord 95:2005 – Establishing

acceptance criteria and preliminary procedures for

accepting waste for storage and the national list of

waste accepted in each class of landfill to be stored

and accepted in landfills, waste must meet specific

characteristics chemicals.

That is why specific analyses were carried out

for the acid tars studied and treated.

Also, the validation of the treatment process by

stabilization-encapsulation of acid tars required the

performance of the leaching test, consists of

bringing the waste sample into contact with a

leaching agent (water) at a certain waste/leaching

agent mass ratio (L/S=2 l/kg or L/S=10 l/kg),

keeping in contact for 24 h, separating the leachate

and analyzing the obtained eluate to determine the

quality indicators pursued.

Analytical determinations were made according

to the following standardized methods:

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1333

Volume 19, 2023

- SR EN ISO16703:2011 – Soil quality.

Determination of the hydrocarbon content in the

C10–C40 range by gas chromatography

- SR EN 16192:2012 – Characterization

of waste. Leachate analysis

- SR ISO 11465:1998 – Soil quality.

Determination of dry substance and water content

relative to mass. The gravimetric method

- SR EN ISO 9377-2-2002 – Water

quality. Determination of the hydrocarbon index

- PSL 70 SR EN ISO 15586:2004 - Water

quality. Determination of lead content. Atomic

absorption spectrophotometric method with graphite

furnace

- SR ISO 10523:2009 – Water quality.

Determination of pH.

To demonstrate the chemical composition and

compositional diversity of this particular waste, the

acid tars from a separate area, different from the

storage tank of a refinery, were investigated.

The analyzed acid tar pit has an area of 6 ha and

was established in 1960.

It comprises 15 smaller pits initially designed to

store residues resulting from crude oil extraction.

Later, residues from refining petroleum products

were also deposited here.

An estimated 80,000 m3 of waste (acid tars, oil

residues, and acid water) is stored in the analyzed

refinery tanks, and until now not to decontaminate

these tanks (Table 1).

In addition to the metal content, the amount of

organic and inorganic products, water content,

sulfur, and acidity were determined.

In addition, the percentage content of the organic

part was analytically determined: the content of

saturated hydrocarbons, aromatics, resins, and

asphaltenes (SARA analysis).

The physicochemical analysis of an acid tar taken

from the refinery analysis battle is presented in the

tables below:

Table 1. The physico-chemical analysis of tar acid

Properties

Gasoline

acid tar

Petroleum

acid tar

Medium

lubricating oil

Density, kg/m3

1,6

1,4

1,2

Total acidity, %

mass

55,4

45,8

18,3

Sulfuric acid

H2SO4, % mass

46,0

33,2

17,3

Water content, %

mass

3,3o

5,6

3,8

Properties

Value interval

Moisture

9 - 15 %

Ash

1 - 5 %

Acidity

15 - 40%

Organic matter

40 - 75 %

Lower calorific value

23550 kJ/kg

Density

1220 kg/m3

Flammability temperature

120 - 160 0 C

5 Treatment of acid

Stabilization/Encapsulation Tars

Stabilization/encapsulation treatment of inorganic

contaminants has been practiced for decades and is

supported by many studies, but much less

information is available on its use on organic

compounds.

Currently, the cement-based stabilization/

encapsulation treatment of organic contaminants is

classified into three categories:

-direct immobilization of organic contaminants,

-immobilization of organic contaminants after

adsorption,

-immobilization of organic contaminants using

oxidizing/reducing agents, [5].

The hydration acceleration efficiency of different

cations is Ca2+ > Mg2+ > Sr2+ > Ba2+ ~ Li+ > K+ >

Rb+ ~ Cs+ > Na+ > NR4+ > H2O, where NR4+ means

the quaternary ammonium ion and H2O means the

absence of the additive.

The published results indicate that:

-calcium has the highest efficiency,

-efficiency depends mainly on the charge

and size of the ion, the most efficient being the

process with minor, highly charged ions, [5].

For highly soluble calcium salts at the same

equivalent concentration, the order of anion

effectiveness is Br- ~ Cl- > SCN- >I-> NO3 -> ClO4->

H2O, which shows a similar trend to that of cations

in terms of size ions.

It should be noted that salts of Zn, Sn, Pb,

soluble phosphates, and fluorides delay the

hydration process, and inorganic salts that form

complexes with calcium also act as inhibitors.

The efficiency of treatment by the

stabilization/encapsulation process of organic

contaminants can be improved by using adsorbents

for the organic components.

Such adsorbents can be incorporated as additives

in the cement mixture or pretreatment before

conventional cement-based solidification.

These additives (residual products of industrial

processes, such as activated carbon, shredded tire

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1334

Volume 19, 2023

particles, and organic clays) can increase the

chemical containment of the contaminant.

Additives such as silica fume and fly ash can

improve the physical retention of organic

compounds by reducing the porosity and

permeability of the waste form.

Activated carbon is commonly used in the

remediation of organics and for capturing many

heavy metals.

The use of activated carbon as a pretreatment

adsorbent in stabilization/encapsulation technology

has yet to be widely reported, probably due to high

costs, but the use of activated carbon in

stabilization/encapsulation technology will expand

because it can be achieved by using regenerated

activated carbon.

In study reported a reduction of organics

concentration to a target level in leachate by

stabilization/encapsulation treatment of organic

contaminants such as creosote, dioxins, and

pentachlorophenol (PCP) using cement formulations

containing activated carbon or other proprietary

reagents at the site American Creosote of Jackson,

TN, [1].

Also, organophilic clays (bentonites, hectorites),

modified to be hydrophobic, with an affinity for

insoluble organic substances, can act as promising

adsorbents for organic contaminants and allow them

to be treated by cement-based solidification, [3].

Modifying clays by exchanging natural cations

(Na+, K+) with organic cations significantly

improves adsorption capacity compared to

unmodified clays.

The water solubility of the contaminant

diminishes the effectiveness of organophilic clays in

immobilizing organic contaminants because organic

molecules adsorb on the organophilic clay surface

by hydrophobic attraction, which is more favorable

when the compound is less soluble in water, [4].

The immobilization of organic compounds in a

cement matrix, with or without adsorbent, is mainly

the result of physical blocking.

Long-term effectiveness for immobilizing

organic contaminants can be achieved by converting

organic waste into less hazardous hydrocarbons.

This leads to a combined process (contaminant

immobilization and degradation).

Data on the long-term performance of applying

stabilization/encapsulation technology at hazardous

waste sites are generally limited.

The environment and long-term conditions to

which the solidified waste is exposed can affect the

stability of the treated waste.

Stabilized cement-based wastes are vulnerable to

the same physical and chemical degradation

processes as concrete and other cement-based

materials; that is, they have the potential to

disintegrate for 50 to 100 years.

EPA's Eleventh Status Report on Treatment

Technologies Used at Superfund Sites shows that

encapsulated and immobilized pollutants has been

implemented at 24% of sites to metal contamination

(174 sites) and organic substances (129 sites), [11].

Current stabilization/solidification systems can

be grouped into the following seven process classes:

- Solidification by adding cement,

-Solidification by adding lime or other pozzolanic

materials,

- Embedding waste in thermoplastic materials such

as bitumen, paraffin or polyethylene,

-Heat-resistant micro-encapsulation,

-Macro-encapsulation of waste in an inert layer,

-Treatment of waste to produce a cement product

with the majority of additions of other constituents,

-Forming a solid mixture by fusing waste with

silica.

It can be noted that the first two methods are the

most frequently used, being suitable for the vast

majority of inorganic process waste.

Treatment costs for the other processes are

generally higher; the latter techniques are applied to

problematic waste, such as radioactive waste or

those with a high organic content.

6 Applicability and Stage of

Development of Stabilization/

Encapsulation Technology

The stabilization/encapsulation technology is a full-

scale commercial technology, and its application

presents the following particularities, [11]:

-stabilization/encapsulation demonstrated its

effectiveness for inorganic contaminants, mainly

metals and radionuclides, in the presence of a low

level of organic materials

-inorganic salts can affect the setting rates of

cement, reducing the strength of the stabilized

product

-stabilization/encapsulation is typically applicable

for situations where the organic content of the

waste/soil, as measured by total petroleum

hydrocarbons (TPH), is more significant than

5,000–10,000 mg/kg, as in some cases, the material

has leached from the cement matrix over several

years:

-the presence of organic contaminants, especially

VOCs, makes the use of stabilization/encapsulation

ineffective,

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1335

Volume 19, 2023

-organic contaminants can volatilize due to the heat

generated during the reaction (leading even to the

need to obtain air emission permits),

-the toxicity of the contaminants in the sediment

does not change,

-the addition of activated carbon and other

adsorbents allows the application of the

stabilization/ encapsulation process at higher

content of organic substances in the treated tar,

-anions can also be immobilized by trapping or

microencapsulation,

-erosion and diffusion processes can favor the

release of contaminants,

-fine particles can bind to larger particles,

preventing the binder from binding effectively,

-the high degree of humidity of the treated tar

influences the application of the stabilization/

encapsulation process (requires increased amounts

of reagents),

- Long-term monitoring is required after applying

the stabilization/encapsulation process.

7 Standards of Remediation,

Assessment and Safety. Long-term

Maintenance of the Application of

the Stabilization/Encapsulation

Process. Remedial Standards

To establish the objectives regarding the

remediation of the contaminated site, there are two

general approaches based on:

-Guidelines or criteria (guidelines and

recommendations),

-Risk assessment (the risk presented by

contaminants both to humans and to the ecological

system),

-With the risk-based approach, each site is assessed

separately.

Factors such as contaminant type and

concentration, as well as possible receptors and

routes of exposure, are considered, and appropriate

concentration limits for individual contaminants are

then set site-specific, [10].

It should be noted that the relative proportions

of waste and other constituents that make up the

"mix" subjected to the stabilization/encapsulation

process vary considerably depending on the

composition and nature of the waste/acid tars,

determining the particularities of the application of

the technology.

If the most appropriate process is selected for a

given situation and a given waste stream,

subsequently published information will likely be of

little help, [11].

Hence, a detailed evaluation of the

stabilization/encapsulation process in the laboratory

is imperative.

In addition, it is necessary to carry out

specific laboratory tests on each waste stream to be

solidified in a specific facility and according to a

specific recipe.

The effectiveness of a

stabilization/solidification process for a particular

waste is correlated and determined according to

three main properties of the treated waste: treatment

or curing time, physical properties, and resistance to

leaching (solubilization) of hazardous components,

[11].

Physical properties such as density and

compressive strength of treated waste are essential

when determining its suitability as a material for

land remediation.

The treated waste's permeability affects the

resistance to the leaching of hazardous components,

which controls the rate of penetration of the

leaching fluid and the rate of leaching of

contaminants into that fluid.

The stabilization/encapsulation process is the

most viable technology for containing contaminated

soils and other hazardous wastes that cannot be

economically destroyed by chemical, thermal, or

biological means.

Unfortunately, published data to verify the

performance and durability of treated waste stored

in landfills over time are scarce and sporadic,

although research shows that the same

environmental concerns that affect the durability of

concrete must be considered when evaluating the

durability and permanence of tar acid-based cement.

In these evaluations, leaching tests and chemical

analyses should be followed by microscopic

analyses that would supplement the data to establish

the long-term performance of the

stabilization/encapsulation process technologies.

Future use of the remediated site and

environmental conditions (natural weathering) may

erode the materials used for contaminant

stabilization, affecting their ability to immobilize

contaminants.

Wastes stabilized by the cement-based

stabilization/encapsulation process are vulnerable to

the same physical and chemical degradation

processes as concrete and other cement-based

materials, [11].

It should be noted that the material treated by

the stabilization/encapsulation process uses concrete

differently from the conventional one in

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1336

Volume 19, 2023

construction; the design of the mixture is based on

the properties of the contaminated environment that

is being treated.

Economic analysis of the

stabilization/encapsulation treatment costs also

includes the transportation of raw and stabilized

waste, the necessary equipment, and labor costs.

Capital and installation costs for inorganic

fixing processes depend on the scale and degree of

complexity of the work required on site.

8 Validation and Monitoring

The validation of the applied remediation process is

based on and involves the same principles for the

remediation of acid tar sites as for other

contaminated sites.

In the case of strategies involving the

removal of acid tars for authorized off-site disposal

or incineration (regardless of whether or not

pretreatment is carried out), it will be necessary to

verify that the removal action has met the agreed

criteria, [10].

This will typically involve sampling at the base

and edges of any excavation to confirm the degree

and extent of any contamination associated with

random sampling in other areas.

If groundwater needs to be remediated (for

example, if there are loose petroleum products),

groundwater monitoring will be required at

appropriate locations around the tar pit.

Monitoring will be required before, during, and

after remediation until the risks are appropriately

managed and until a valid statistical data set has

been produced that demonstrates that the

concentrations are within the limits and that the

evolution trends are acceptable.

Current legislation stipulates that any

remediation be associated with a post-remediation

monitoring plan - documentation in which the post-

remediation activities are described, to verify the

achievement and maintenance of the proposed

remediation targets and objectives at the end of the

remediation, respectively the evaluation of all

components of the remedied geological

environment.

9 Research on the Treatment of

Contaminants by Applying the

Stabilization/Encapsulation

Process. Assessment of the Risk due

to Acid Tars

The published investigations summarize the

mechanisms involved in the immobilization process

of As, metals (Zn, Cr, Cu, Pb, Cd, etc.), and PAHs

and present the specific results from laboratory and

field experiments obtained by applying the

stabilization process/ encapsulation.

Toxicity Characteristic Leaching Procedure

(TCLP) applied to sludge containing solids using

four different binder systems consisting of cement

mortar, fly ash, clay, and lime and cured for 28 days

showed that the volume of sludge added, which

resulted in maximum metal stabilization was 60%

for all combinations, above which the metal fixation

efficiency decreased, resulting in high zinc values in

the leachate.

In the immobilization of Cd by stabilization/

encapsulation process technology using a mixture of

sand, cement, and clay, it was found that clay

increased the metal absorption capacity.

In contrast, sand and cement improved the

compressive strength, [11].

Exciting experiments were devoted to studying

the mobility and availability of metals stabilized by

using zeolites in contaminated soils.

The amount of dissolved Cu, and thus its

mobility, was strongly reduced, and the percentage

of metal-stabilized in the solid phase increased over

time, reaching values of 30 and 40% at 30 and 60ºC,

respectively, after fixing, [11].

In addition to the publication of specific,

particular cases, current knowledge in the field of

cement within the stabilization/encapsulation

process is also disseminated, focusing on the

chemistry of cement, the effects of inorganic and

organic compounds on cement hydration, and the

immobilization mechanisms of different organic and

inorganic compounds.

For the treatment of organic contaminants,

using adsorbents such as organophilic clay and

activated carbon, either as pretreatment or as

additives in the cement mixture, can improve the

immobilization of waste contaminants.

It has proven effective in immobilizing organic

contaminants related to activated carbon but is

generally too expensive for routine use.

A study on the use of powdered activated carbon

to prevent leaching of organics from

solidified/stabilized waste forms showed that the

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1337

Volume 19, 2023

addition of 1% activated carbon reduced the

leaching of some organic contaminants (phenol, 2-

chlorophenol, chlorobenzene, aniline, and methyl

ethyl ketone) by more than 70%.

In comparison, an addition of 2% contributed to

a reduction of less than 1% for most organics, [7].

Various studies note that the degradative

stabilization/encapsulation variant, which combines

chemical degradation with the conventional

stabilization/encapsulation process, is promising.

However, further studies are needed to assess its

technical and economic feasibility.

Acid tars can threaten human health and the

environment due to their acidity, volatiles, and other

hazardous components.

Tar acid spills can occur through direct contact,

outgassing, off-site bulk migration of tar, and

contamination of surface and groundwater, [8].

The leaching and migration phenomena of acid

tars associated with natural weathering have

demonstrated that acid tars can leach significant

levels of contaminants if disturbed. In contrast, the

level of leaching is significantly lower in the water

table. Public risk perceptions of acid tar deposits

may diverge from anticipated reactions and

professional risk assessment. How the public

perceives contamination risks is essential to

managing contaminated sites. Although the public is

generally unaware of the chemical composition of

tar acids and their associated risks, those who live

near sites contaminated with tar acids can

"familiarize" themselves with constant pollution.

In addition, the experience of low probability

and delayed-effect risks—such as health effects

from contamination—tends to produce an

underestimation of the risk presented.

In this context, the acid tar battle can be seen,

visited up close, etc., without any visible adverse

effects. This experience may lead people to feel the

need to ignore experts' warnings about the dangers

of tar acids.

Taking into account (the risk of accident), in

particular, the substances used and the technologies

used, from the point of view of security, the

remediation of acid tar battles involves several risk

factors, [12]:

- The content of the battles,

- Potential VOC and SO2 emissions,

- The instability of the battlements' dykes,

- The possible presence of other deposited

dangerous materials (e.g., unexploded wartime

ammunition),

- Nearby pipelines with flammable and explosive

products,

- Human settlements in the vicinity, with some

houses located right next to the fence of the

refinery, in the area of the battles,

- Carrying out other economic activities in the

area of remediation.

To work safely in the application of the

remediation methods of acid tar battles, it is

necessary to act in stages, according to the hierarchy

of prevention: risk reduction, collective protection

measures, personnel protection measures, personnel

training, instructions, and means of prevention.

10 Additives used for the Stabilization/

Encapsulation of Acid Tar

Based on literature data and consultation of

published patents [US 20140249346, US5700107,

US20140249346, EP0655493, US5049256,

GB1501572, US20140249346, US5700107,

US20140249346, US5700107, EP1868747

EP1868747, US2012253094, US5049256,

GB1097565, GB150157], for treatment by the

method of stabilization/encapsulation chosen and

applied to acid resins, the following substances were

used as additives and filler materials: cement, sand,

calcium oxide, sodium hydroxide, bentonite,

emulsifying detergent, strengthening additives,

absorbent, and sodium metasilicate.

The rest, up to 100%, is represented by acid tar

subjected to stabilization.

Potentially applicable reagents were identified

before lab-scale treatability testing.

Identifying the potentially applicable reagent

depends on several factors, including the

contaminant being treated, the concentration of

contaminants in the acid tar, the geotechnical and tar

properties, required performance parameters, and

minimum acceptable performance criteria for the

treated tar.

The identification and practical choice of the

reagents applied in the experiment were based, on

the one hand, on the consultation of the technical

literature carried out in the theoretical research and,

on the other hand, on the author's experience in the

implementation of stabilization/encapsulation

projects.

Several candidate reagents were thus identified,

narrowing down the number of reagents based on

low-cost and less time-consuming treatability tests.

The selection of candidate reagents was based on

the knowledge and analysis of chemical

interferences and incompatibilities of the chemical

behavior of the metals in the tar, but also taking into

account the cost and history of the process.

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1338

Volume 19, 2023

The composition for neutralization,

stabilization, and encapsulation of acid tar with TPH

values below 200,000 mg/kg and DOC below 1000

mg/kg dry substances., according to research, is

represented in the adjacent table (Table 2).

Table 2. The composition for the neutralization,

stabilization, and encapsulation of acid tar

Component

(%)

Cement

3-20%

Sand

2-5%

Lime

3-8%

Sodium hydroxide

1% - 10%

Bentonite

1-2,8%

Emulsifying detergent

1-2%

Strengthening additives

Sodium metasilicate was added in proportions

ranging from 0.3 to 0.8%.

As argued in the literature, the final performance of

the stabilization/encapsulation technology

application is determined by the quality and intrinsic

properties of the additives and binders in the

treatment recipes.

The ordinary Portland cement (CPO) used in

the present study allows the immobilization of Cr,

Cu, Zn, Mn, and Pb.

The addition of cement leads to an increase in the

degree of immobilization with an increase in the

curing time of the hardened material. This reference

is attributed to the pozzolanic or

pozzolanic/hydraulic properties of the cement on the

microstructure of the hardened material. Additives

added to cement and the hydration reactions in the

mixtures favor the formation of the specific

microstructure, favoring the immobilization of

dangerous elements.

The sand is used as an additional aggregate that

forms a hard layer covering tar contaminants in the

presence of cement and water.

Calcium oxide (slaked lime, quicklime),

presented as a white powder, was used to neutralize

acid tar. In addition to the neutralizing effect, the

calcium oxide and the emulsifier contributed to the

transition of the metals from the volatile phase to a

stable phase.

The added lime favors the immobilization,

especially of Cd, Cu, Ni, Pb, and Zn.

Sodium hydroxide neutralized the tar, and the

reaction was strongly exothermic.

The emulsifying detergent stabilizes the pH and

obtains a homogeneous mixture of the stabilized tar.

By breaking the hydrocarbon chains and embedding

the ingredients faster and deeper, the presence of the

emulsifying detergent leads to a higher degree of

encapsulation of the tar.

To mix and incorporate all the ingredients

proposed in the recipes elaborated in the thesis, in a

short time, the emulsifying detergent was used

according to the Brand Registration Certificate no.

107443, granted by the STATE OFFICE FOR

INVENTIONS AND TRADEMARKS.

Bentonite and cement contribute to the

hardening/encapsulation of the acid tar and the

additional retention of Pb.

The absorbent is used to reduce the volume of

the treated tar.

The added sodium metasilicate had a water-

scavenging effect. Sodium metasilicate is not a

cleaning agent per se but is a strong base that reacts

violently with acids. It was added to elaborate

recipes because it maintains the added emulsifier's

and absorbent's cleaning efficiency, mainly by

inactivating water hardness.

It has also been reported that Cu can bind

cement using this agglomerating agent, sodium

metasilicate, Na2SiO3 9H2O.

The freshly prepared tar sample is homogenized,

and binders are added to stabilize and encapsulate

the acid tar.

After completing the treatment in the laboratory,

the stabilized tar is presented as a compacted block.

The values of the pollutants identified in its

leachate fall within the maximum values allowed

according to Order 95/2005.

The final processing and verification found that

a stabilized and encapsulated material with low

permeability, low leachability, and moderate to high

resistance was obtained, which meets all the

performance criteria.

The volume of the treated tar shows an increase

of up to 5% of the initial volume of the acid tar

before treatment.

This aspect is essential in the further

valorization stage of the research because it will

allow the tar to be treated in situ, using only the

limited space of the existing pits, without digging

additional pits to store the surplus resulting from

treatment.

Since acid tar is a particular waste, its treatment

by stabilization/encapsulation had to be carried out

carefully (see the literature study).

First, being unstable from a geotechnical point

of view, it can show creep effects depending on the

type and temperature.

Secondly, leaks of organic compounds

(hydrocarbons) and inorganic compounds (sulphuric

acid, metals) can be recorded in contact with water.

After adding and mixing the additives, no

significant heating of the neutralized and treated

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1339

Volume 19, 2023

acid tar, leading to volatilization of specific

contaminants, was observed.

Also, no sulfur dioxide emissions were detected

since it was an "old" tar. Since it was not intended

that the tar thus treated and stabilized be exploited

as a construction material, in the thesis, it was not

analyzed from a geomechanical point of view.

Contaminants once immobilized in the matrix, do

not migrate as long as the integrity of the matrix is

maintained. The leachate from the disposal site was

analyzed to monitor any contaminant migration.

As mentioned, from the field under study, acid

tar samples were taken, and their composition was

determined, following the following indicators: pH,

THP, metals, cyanides, chlorides, DOC, and sulfates

and were compared with the imposed limit values

by Order no. 95/2005.

For all locations, the depth of acid tar samples

was within the range of approx. 5-30 cm.

11 Formulation of Stabilization/

Encapsulation Treatment Recipes

Given the high values above the legal limits of the

mentioned indicators, several recipes were

formulated, prepared, and tested, of which three

representative recipes were retained in the end.

After each recipe, several different portions of acid

tar were mixed and tested. The samples were tested

for the curing process as a function of time by visual

examination and portable penetrometer tests. The

testing process was stopped for recipes that did not

show good results. As a result of the limited success

in earlier tests, the additives were dried and mixed

in subsequent tests (Table 3).

The three formulated recipes stand out for:

- Constant concentrations of strengthening

additives, absorbent, and sodium hydroxide

(approx. 1% each)

- Variable amounts of emulsifying detergent,

produced by Eurototal (1; 3.5 and 4%

respectively)

- Increase in cement concentration (from 3% in

recipe 1 to 8% in recipe 3)

- The added calcium oxide varies from a

concentration of 8% in the case of the first

recipe to 7% in the formula of recipe 3

- Increasing the concentration of bentonite (from

1% in recipe 1 to 2.8% in recipe 3)

- A relatively constant increase is noted for

sodium metasilicate (0.30%, 0.50%, and 0.80%,

respectively - recipe 3).

Table 3. The representative recipes for treating the

acid tar tested

Compound

Recipe 1

Recipe 2

Recipe 3

Sodium metasilicate

0,30%

0,50%

0,80%

Emulsifying detergent

3,5%

4,0%

Lime

3,00%

7,00%

Magnesium oxide

0,1%

0,2%

0,3%

Bentonite

2,8%

Sand

Cement

Strengthening additives

Absorbing

Sodium hydroxide

For tars with high pH and low THP values,

recipe 1 applies. Recipe three is used for cars with

low pH values and high THP values. For tars with

medium TPH values, recipe 2 gave the best results.

It was found that THP and pH values and other

indicators, including the concentrations of various

metals in the initial tar, influence the efficiency of

the recipe used.

Therefore, if the application of the chosen recipe

did not decrease concentrations below the limits

provided for in Order 95/2005, one of the other two

recipes is used.

The third recipe is used if even the second

recipe does not give the expected results. All these

attempts were completed by obtaining two patents,

one international and the other national. After

applying the recipes according to the inventions, a

significant decrease in the parameters was found,

and compliance with the norms provided by Order

No. 95/2005.

12 Conclusion

The analysis and discussion of the experimental data

led to the following conclusions:

The pH. The pH values measured for the acid tar

stored in the studied area range from 0.20 to 5.20.

The strongly acidic character has intensified, from

the already acidic character of the categories of

potential waste stored in the studied area (sludge, oil

sludge with pH values between 3.9 and 5.6) to that

due to the mixture of these wastes with the tar acid.

The TPH (total hydrocarbons in soil) values vary at

different depths within the same plot, with a slight

tendency to decrease in depth from the soil surface,

with 61 samples out of 82 having a higher

concentration of TPH at a depth of 30 cm.

Specifically, according to the analyses, the THP of

the unstabilized acid tar is between 48,333 and

477,062 mg/kg dry substances, with 59 samples

with TPH content values lower than 200,000 mg/kg

dry substances.

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1340

Volume 19, 2023

The highest concentration of TPH detected for

all acid tar samples was 477062 mg/kg dry

substances, which indicates the highest level of

actual contamination in a sample corresponding to a

depth of 5 cm.

The concentration of TPH decreased for the

same point, at a depth of 30 cm, by about four times.

The study of TPH concentrations under the

conditions of the application of large-scale

application of cement-based stabilization/

encapsulation technologies to inorganic waste,

including metal, is essential in the conditions in

which it has been reported that organic substances

can be easily leached.

Unfortunately, little information is available on

organic leaching from acid tars after applying

stabilization/ encapsulation technology or on the

effects of organics on complex setting reactions,

which can result in an altered cement matrix.

It was found that the films formed by

asphaltenes are resistant to acidic environments (low

pH) and become less persistent as the pH increases.

In the alkaline environment, these films become

very weak, unstable, or even move into a mobile

state. Films formed by resins are more vital in basic

environments and weak in acidic environments.

Metal content

As stated, the acid tar samples were digested with

nitric acid to make the metals available for

determination.

The concentrations of the analyzed metals were

established according to the Analysis Method SR

EN ISO 15586:2004: Determination of trace

elements by atomic absorption spectrometry with a

graphite furnace and the method for the rapid

detection of trace elements.

The equipment used was the Atomic Absorption

Spectrometer with a graphite furnace and the

Mobile EDXRF Device with X-ray detection to

detect trace elements rapidly.

The different and, of course, sometimes high

levels of metal concentrations in the untreated acid

tar samples can be attributed to the concentrations of

such metals in the wastes stored in pollution areas,

in the additives used in the refining processes, the

absorption of metals from the storage tanks and the

supply, the natural presence of metals in the parent

rock from which the crude oil was extracted and

even in the materials with which the

stabilization/encapsulation is carried out (e.g.,

cement).

Pb (lead). The value of 50 mg/kg, the legal limit of

Pb (lead) in the soil, was exceeded for 81 samples

(out of a total of 82); 11 samples have a Pb (lead)

content higher than 500 mg/kg (of which four

samples exceeding 1000 mg/ kg), and the rest

having a Pb (lead) content between 42 and 478

mg/kg.

The Pb (lead) concentrations analysis shows a

strong infestation of some samples collected from

the depth of 5, where the maximum value of 2235

mg/kg was reached.

Cd-Cadmium concentrations in untreated acid tar

are between 1 and 126 mg/kg dry substances; 72

samples exceed the limit value of 5 mg/kg, four

samples with concentrations above 50, and 2

samples with concentrations above 100 mg/kg.

The copper (Cu). The concentration of copper (Cu)

varies between 2.6 and 789 mg/kg of dry

substances, with the only critical point being a level

much higher than the legally imposed value of 100

mg/kg.

Chromium (Cr). For the total chromium (Cr)

content, the legal limit value is 70 mg/kg, and the

total chromium (Cr) content determined in untreated

acid tar varied between 3 and 452 mg/kg dry

substances.

Nickel (Ni). With a content variation from 2 to 859

mg/kg, 40 mg/kg is exceeded only in three points

where very high values are recorded, of 859 and 528

(for depths of 5 and 30 cm). Seventy-four samples

from 82 samples have values lower than 20 mg/kg.

Arsenic (As). The content of Arsenic (As) in the 82

samples of untreated acid tar varies from 1.4 to 589

mg/kg.

For Arsenic (As) content, the allowed value of

25 mg/kg provided for in Order 95/2005 is exceeded

for 52 samples.

As a general finding, it is noted that the values

determined and recorded for the concentrations of

metals Pb+Cd+Cu+Cr+As.

However, in the initial acid tar, their values

were above the maximum allowed limits; in the

leachate stabilized at one day, they recorded low

values, some even below the quantification limit of

the determination methods.

13 Leachate Analysis and Evaluation.

Analysis of Eluates

The leachates were prepared and analyzed from the

treated acid tars according to the leaching procedure

SR EN 16192:2020 Waste characterization—

analysis of eluates.

The pH. The analysis of the eluates to determine the

acidity according to SR EN ISO 10523:2012 pH

determination. As a general remark, it was found

that increasing the pH from values between 0.2 and

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1341

Volume 19, 2023

5.28 (untreated acid tar) to values from 8.7 to 10

(the case of the leachate) had a beneficial role in

increasing the leaching performance (e.g., in the

speciation of metal contaminants).

The TPH (total hydrocarbons in soil) content,

corresponding to the leachate, was determined by

Method: SR EN ISO 9377-2-2002—determination

of the Hydrocarbon Index.

The stabilization-encapsulation technology, applied

in the study for the treatment of acid tar, confirmed

the fact that the organic materials - hydrocarbons do

not react with the inorganic binders from the three

applied recipes due to the significant differences in

hydrophobicity and polarity between the organic

contaminants and the organic binders.

In many cases, this could lead to ineffective

immobilization of hazardous organic hydrocarbon

contaminants in the solid matrix and significant

leaching of many contaminants.

However, the final results of the leaching tests

showed good efficiency in reducing the TPH (total

hydrocarbons in soil) content in the leachate

Metals. The concentrations of metals from the

Pb+Cd+Cu+Cr+As group were also monitored in

the leachate, and the following were mainly found:

- The leachate preparation and analysis were done

according to SR EN 16192:2020 waste

characterization. Analysis of eluates.

The leaching of heavy metals is the main reason

stored acid tars and managed

encapsulated/stabilized products should be classified

as hazardous waste.

- The Ordinary Portland cement (CPO) used in the

present study contributed to the immobilization, in

particular, of Cr, Cu, Zn, Mn, and Pb. The addition

of cement leads to an increase in the degree of

immobilization with an increase in the curing time

of the hardened material. As a result of the high pH

of the cement, the metals are retained in the form of

insoluble hydroxide or carbonate-type salts from the

hardened structure.

- In addition to the neutralization effect, the calcium

oxide and the emulsifier in the formulated recipes

contributed to the transition of the metals from the

volatile phase to a stable phase. The added lime

favors the immobilization, especially of Cd, Cu, Ni,

Pb, and Zn.

- Studies have shown that lead, copper, zinc, tin, and

cadmium will likely bind in the matrix by chemical

fixation, forming insoluble compounds. At the same

time, mercury is predominantly retained by physical

microencapsulation. On the other hand, organic

contaminants interfere with the hydration process,

reduce the final strength, and are not easily

stabilized, delaying the formation of the crystalline

structure and resulting in a more amorphous

material. Reducing the interference of organic

contaminants with cement hydration and improving

stabilization can be done by incorporating modified

and natural clays or sodium silicates into the

stabilizing mixture with the cement.

- The different elements in the formulated recipes

presented different leaching potentials correlated

with the curing period, the compositions of the

binders, and the initial and final pH, suggesting that

the preliminary release behavior of each

contaminant metal should be considered for the

practical immobilization of the contaminated

materials.

- The applied encapsulation technology favored

decreased mobility of cadmium, copper, chromium,

lead, nickel, and arsenic metals in acid tar. A drop in

concentration of over 95% was obtained for the

whole group of tracked metals. Thus, the results of

the leaching test show that the level of metal

concentrations is much lower than the pollution

limits stipulated by international standards (ISO et

al.) and Romanian Standards Order 95/2005.

- As a general finding, also noted in the published

literature, the leaching of some heavy metals largely

depends on the pH of the liquid (Ex. Pb and Cr).

Pb (lead) varies between 0.0003 and 0.0056 mg/kg

in all stabilized samples.

It should be noted that the pH of the samples from

which the metals are determined varies from 8.7 (at

a Pb (lead) content of 0.008) to 10.0 (at a sulfur

content of 0.002 mg/kg Pb (lead)).

It can be seen that a high pH affects the

precipitation of Pb (lead).

The concentration of Pb (lead) in the eluate will

decrease with increasing pH due to the cement in

the mixture used for stabilization/encapsulation.

Unfortunately, it was found that Pb (lead) is

difficult to detect in the eluate when the pH is

between 9 and 11 due to the formation of insoluble

hydroxide. However, it can be detected at pH 12 due

to the formation of an amphoteric hydroxide

complex.

Cadmium- Cd concentrations in the eluate samples

varied between 0.0001 and 0.0050 mg/kg.

Most eluate samples (approx. 87%) are

contaminated with less than 0.002

mg/kg Cadmium- Cd.

The studied acid tar samples subjected to leaching

contain a significant content of Cadmium- Cd with

an average of about 30 mg/kg.

Cadmium- Cd leaching for all samples shows that

the values of the concentrations of this metal were

quite scattered, with values below 0.001 mg/kg for

the first nine samples, a maximum in the case of

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1342

Volume 19, 2023

sample 10 (0.005 mg/kg) and values below 0.002

mg/kg for the samples 12-39.

Also, cadmium hydroxide has a low solubility at pH

10 in a short solidification time.

As mentioned in the literature, cement is beneficial

for Cadmium-Cd immobilization in all conditions.

A decrease in Cadmium- Cd migration with

increasing pH is probably attributed to Cadmium-

Cd commonly existing as hydroxide on

cementitious materials; therefore, higher pH

conditions accelerated the formation of the insoluble

Cd(OH)2 precipitate.

A variation of the Copper (Cu) is detected in a

concentration from 0.00083 and 0.0161 mg/kg,

The leachate's copper (Cu) concentrations are

approximately 85% lower than 0.008 mg/kg.

Although it was found in the literature that the pH

value does not influence

In copper (Cu) elution, which, when leaching the

same sample, would have a general behavior

like Chromium (Cr), the values of Chromium

(Cr) concentrations are about five times higher. An

explanation of the lower concentrations of Copper

(Cu) in the leachate resulting from the acid tar

treated by encapsulation/stabilization would be the

application of some recipes in which the

agglomeration agent, sodium metasilicate,

Na2SiO3.9H2O, was added in larger quantities.

Chromium (Cr). Chromium, known as one of the

most toxic metals, Chromium (Cr) measured in the

eluate collected after acid tar treatment varies

between 0.0010 and 0.084 mg/kg.

As in the case of copper, very high values

of Chromium (Cr) concentrations are found (over

330 mg/kg), and none of the three recipes could

achieve the appropriate reduction of Chromium

(Cr) in the eluate.

Although Chromium (Cr) concentrations in the

range of 30 to 100 mg/kg can be found in ordinary

Portland cement, concentrations that can be added to

those found in acid tar, the application of the three

recipes formulated and applied in the treatment of

acid tar led to values below 0.1 mg/kg chromium in

leachate.

A noticeable trend for all samples can be observed

when the cement content increases the Chromium

(Cr) concentration.

This is due to the cement containing Cr6+, as the

literature mentions.

At the same time, the additional presence of Cr6+

increased the cement's initial and final setting times.

It was concluded that the immobilization of Cr6+ by

the cement-based encapsulation/stabilization

technology was achieved due to the formation of a

complex calcium chromate (CaCrO4) with low

solubility.

The cement hydration process was affected in the

presence of Cr6+ because part of the Ca2+ in the

cement reacted with CrO42–.

Nickel (Ni) concentrations in the eluate varied

between 0.0015 and 0.091 mg/kg dry substances.

It is found that the hydroxides of Nickel

(Ni) and Cadmium (Cd) are incorporated in the

hydrated cement matrices, which gives a good

immobilization capacity for Nickel (Ni).

Arsenic (As). It is distributed over a wide range of

values in the untreated tar (between 1.4 and 589

mg/kg dry substances) and in the eluate (below

0.001 to 0.402 mg/kg).

The sample with 2 % cement gave a higher Arsenic

concentration (As) than 0 % and 4 % cement.

For 4 % cement with different rubber chip content,

the concentration of arsenic (As) also increases

significantly.

This could be the leaching of As upon the formation

of Ca-As precipitates.

Therefore, Ca-As precipitation increases with Ca in

the cement.

Increasing the pH of the leachate, on the one hand,

and the addition of CaO, on the other hand, favors it

better.

As fixation when the leaching takes place in an

alkaline environment.

Also, high As concentrations were in samples 21

and 24, in which the TPH content in the acid tar was

high. Cyanides.

To determine the content of free cyanides in the

eluted water, a UV-VIS Spectrophotometer DR

3900 was used to detect cyanides with

concentrations between 0.01 mg/l and 0.6 mg/l.

Cyan concentrations between 0.013-0.368 mg/kg

s.u. in the untreated acid tar reached concentrations

< 0.001 below the detection limit in the leachate.

Chlorides, Sulfates, DOC (Dissolved Organic

Compounds). Related to the content of chlorides,

sulfates, and DOC, determined in the leachate, there

is a reduction in the concentration of these

substances with maximum values at sampling point

20, at a depth of 30 cm for DOC, respectively

sulfates (2047, respectively 619 mg/kg).

The DOC content was between 108 and 2047 (with

three values above 1000 mg/kg).

According to this research, the macro-scale

application of the process for the stabilization and

encapsulation of acid tar with TPH values below

200,000 mg/kg would allow the metal content from

the group considered Pb+Cd+Cu+Cr+As to decrease

below the imposed limits and DOC below 1000

mg/kg s.u.

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1343

Volume 19, 2023

The technological flow of the model is based on

the following technological phases: supply of the

material to be treated, dosing of treatment agents,

aeration, homogenization, heating and maintaining a

constant treatment temperature, controlling the

technological parameters during the treatment

process, and extracting the treated product.

In perspective, it is aimed to fulfill the objectives

of future research:

- Add to evaluations based on leaching and chemical

analysis the use of all microscopic analyses in

studies of the long-term performance of

stabilization/encapsulation technologies in the

treatment of acid tars in the petroleum industry

- Classic extraction techniques (e.g., Soxhlet),

already applied, to be completed and compared with

new techniques (e.g., extraction with ultrasound,

microwaves), thus capitalizing on the expected

advantages related to the reduction of treatment

times, extraction, the number of additives, the use of

some waste as additives.

- The complex research which, in addition to the

analyses focused until now, mainly on the inorganic

components of the tar, should also add an organic

analysis of the leachates, under the conditions in

which the leaching tests would have a more realistic

character, being carried out on batches with

conditions adjusted (stirring time, water-solid ratio,

temperature)

- For the statistical processing part, the analysis of

several candidate mathematical models will be

sought, as well as the evaluation function, and the

mathematical model with the minimum value of the

absolute average error will be chosen.

- Additional design and implementation of

weathering tests of a different nature to foreshadow

how acid tar transforms under different conditions,

raising the possibility that a particular damaged

form may become part of a potential remedial

solution.

References:

[1] Alshammari J.S., Gad F.K., Elgibaly A.A.M.,

Khan, A.R., Solid waste management in

petroleum refineries, American Journal of

Environmental Sciences, 4, 2008, pp. 353-

361,

https://doi.org/10.3844/AJESSP.2008.353.361

[2] Speight, J.G., The Chemistry and Technology

of Petroleum, 5th Edition, Boca Raton, CRC

Press, 2014, pp.112-143, [Online].

https://books.google.ro/books/about/The_Che

mistry_and_Technology_of_Petroleu.html?id

=ZDPOBQAAQBAJ&redir_esc=y (Accessed

Date: February 9, 2024).

[3] Riazi M. R., Characterization and Properties

of Petroleum Fractions, 2005, ASTM

International, [Online].

http://www.riazim.com/sample/MNL50.pdf

(Accessed Date: February 9, 2024).

[4] Obiajunwa E.I., Pelemo D.A., Owalabi S.A.,

Fasai M.K., Johnson-Fatokun F.O.,

Characterisation of heavy metal pollutants of

soils and sediments around a crude oil

production terminal using EDXRF. Nucl

Instrum Methods Phys Bull 194, 2002, pp.61–

64.

[5] Onuţu I., Tita M., Soil contamination with

petroleum compounds and heavy metals- case

study, Scientific Papers. Series E. Land

Reclamation, Earth Observation &Surveying,

Environmental Engineering, Vol. VII, 2018,

pp. 140-145,

[6] Gallego J. R., Sierra C., Villa R., Pelaez I.

Ana, Sanchez J., Weathering processs only

partially limit the potential for bioremediation

of hydrocarbon – contaminated soils, Organic

Geochemistry, 41, 2010, pp. 896-900.

[7] Johnson O. A., Affam A. C., Petroleum

sludge treatment and disposal: A review,

Environ. Eng. Res. 24 (2), 2019, pp. 191-201.

[8] Lima C., Lima R., Silva E., Castro K. C.F.O,

Soares S., Araujo A., Analysis of Petroleum

Oily Sludge Produced from Oil-Water

Separator. Revista Virtual de Química. 6.

2014, 10.5935/1984-6835.20140076.

[9] Mulligan C.N., Yong R.N., Gibbs B.F.,

Remediation technologies for metal-

contaminated soils and groundwater: an

evaluation. Engineering Geology, 60, 2001,

pp.193-207.

[10] Obiajunwa E.I., Pelemo D.A., Owalabi S.A.,

Fasai M.K., Johnson-Fatokun F.O.,

Characterisation of heavy metal pollutants of

soils and sediments around a crude oil

production terminal using EDXRF. Nucl

Instrum Methods Phys Bull, 194, 2002, pp.

61–64.

[11] Vdovenko S., Boichenko S., Kochubei V.,

Composition and Properties of Petroleum

Sludge Produced at the Refineries, JCCT,

Vol. 9, No. 2, 2015, pp.24-35.

[12] Hochberg S., Tansel B., Laha S., Materials

and energy recovery from oily sludges

removed from crude oil storage tanks (tank

bottoms): A review of technologies.

Australasioan Journal of Environmental

Management, Vol. 305, March 2022, 114428.

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1344

Volume 19, 2023

[13] Khan Z., Troquet J., Vachelard C., Sample

preparation and analytical techniques for

determination of polyaromatic hydrocarbons

in soils, Int. J. Environ. Tech., Vol. 2, No.3,

2005, pp. 275-286.

[14] Frolov A.F., Aminov A.N., Timrot S.D.,

Composition and properties of acid tar and

asphalt produced from acid tar, Chem. Tech.

Fuels Oils, 17, 1981, pp. 284–288.

[15] Puring M. N., Neyaglov A.V., Kruglova T.A.,

Bituleva N.A. Gorbacheva N.A., Startsev

Y.V., Composition of acid tars from

production of oils, Chem. Tech. Fuels Oils,

26, 1990, pp.32–35.

[16] Banks D., Nesbit N.L., Firth T. Power S.,

Contaminant Migration from Disposal of Acid

Tar Wastes in Fractured Coal Measures

Strata, Southern Derbyshire, Special

Publication, vol. 128, Geological Society,

London, 1998, pp. 283–311.

[17] Slater D., Boys from the Black Stuff,

SUSTAIN’ Built Environ. Matters, 4, 2003,

pp. 39–40.

[18] Wiles C.C., A review of

solidification/stabilization technology. J.

Hazard. Mater., 14(1), 1987, pp 5–21.

[19] Leonard S., Stegemann, J., Amitava R.,

Characterization of acid tars, Journal of

Hazardous Materials 175, 2010, pp. 382–392.

[20] Kerr K., Probert S. D., Fluidised-bed

incineration of acid tar wastes, Appl. Energy,

35, 1990, pp. 189–243.

[21] Python Software Foundation. Python

Language Home Page. 2020, [Online].

www.python.org (Accessed Date: February 9,

2024).

[22] Ministry of the Environment and Water

Management. "Order no. 95 of February 12,

2005, regarding the establishment of the

criteria of acceptance and preliminary waste

acceptance procedures at storage and the

national list of accepted waste in each class of

landfill", [Online].

https://legislatie.just.ro/Public/DetaliiDocume

ntAfis/59751 (Accessed Date: February 21,

2024).

Contribution of Individual Authors to the

Creation of a Scientific Article (Ghostwriting

Policy)

- Mihaela Tita, and Daniel Tita carried out the

concept of acid tar capsulation.

- Ion Onutu, Timur Chis analysis of this project and

experimental research procedures analysis.

- Timur Chis and Lucian Ion Tarnu were

responsible for the Statistics.

Sources of Funding for Research Presented in a

Scientific Article or Scientific Article Itself

No governmental funding was received of this

paper.

Conflict of Interest

The authors have no conflicts of interest to declare.

Creative Commons Attribution License 4.0

(Attribution 4.0 International, CC BY 4.0)

This article is published under the terms of the

Creative Commons Attribution License 4.0

https://creativecommons.org/licenses/by/4.0/deed.en

_US

WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT

DOI: 10.37394/232015.2023.19.120

Mihaela Tita, Daniel Tita, Ion Onutu,

Timur Chis, Lucian Ion Tarnu

E-ISSN: 2224-3496

1345

Volume 19, 2023