Solidification and Stabilization

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Solidification and stabilization of chromium laden wastes in cementitious

binders

ABSTRACT

Solidification/stabilization (S/S) technology was applied to a simulated sludge containing

chromium. Leaching tests such as toxicity characteristic leaching procedure (TCLP), ANS

16.1 and multiple TCLP tests conducted on stabilized blocks showed that chromium was

immobilized by the binder studied. A linear relationship was obtained between the

cumulative fraction of chromium leached and time1/2 in the stabilized samples proving that

chromium is leached by diffusion. The leachability indices obtained for the solidified

materials satisfy the guidance value as per US Nuclear Regulatory Commission. Chromium

concentrations in the TCLP leachates were well within the regulatory levels of the United

States Environmental Protection Agency. Microchemistry and morphology of the stabilized

samples were studied using Fourier transformation infrared (FTIR) technique and scanning

electron microscopy (SEM).

MATERIALS AND METHODS

Four different kinds of binder materials, Portland cement, Portland cementfly ash, Portland

cementlime and Portland cementgypsum were used for solidification of a synthetic metal

containing waste. The cement used was of grade 43 and fly ash was obtained from a coal-

based thermal power plant. Lime (Ca(OH)2) and gypsum hemi hydrate (CaSO41/2H2O)

were purchased from the local market at Chennai, Tamil Nadu. The composition of the

Portland cement, fly ash, lime and gypsum used is presented in Table 1. Heavy metal

concentrations were found to be negligible in the binders.


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Table 1 Chemical compounds of binder materials

The sample preparation has been explained earlier15. The mix ratios prepared were:

C (10.26% CrCl3 6H2O; 89.74% cement),

FC (10.26% CrCl3 6H2O; 10% fly ash; 79.74% cement),

LC (10.26% CrCl3 6H2O; 10% lime; 79.74% cement) and

GC (10.26% CrCl3 6H2O; 10% gypsum; 79.74% cement).

All the analyses were done in duplicate and the average results are presented. Toxicity

characteristic leaching procedure (TCLP) of unsolidified and solidified wastes was carried

out by extracting at a liquid to solid ratio of 20 : 1 using TCLP leaching fluid as medium. The

solidified samples after crushing to size < 9 m along with leaching fluid were placed in a

rotary shaker for 18 h. The samples were filtered and analysed for metals. Other aggressive

leaching tests, viz. multiple TCLP (MTCLP) and ANS 16.1 test were performed on two-

month-old sample. Diffraction coefficient (De, cm2 s1) and leachability index (LI) were

calculated from eqs (1) and (2).

CFL=an/A0 =2(S/V) (Det/ ) , (1)

LI = logDe, (2)

Where an is the total amount of substance released in all leaching periods of time t, A0 the

total amount of substance originally present, Vthe volume of waste, Sthe surface area of the

waste.


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RESULTS

Results of the TCLP test:

Table 2 Concentration of chromium by TCLP

The pH of the leachate ranges from 4.5 to 5.0. It is clearly seen that as the curing time

increases the fixation of chromium also increases. Chromium levels in all the mix ratios on

the 14th day of curing are less than the TCLP regulatory value (5 mg l1), demonstrating that

chromium is well fixed in all the systems studied. The cementgypsum system has excess

sulphate, which may be responsible for the impedance in the fixation of chromium. Fly ash

acts both as a fine aggregate and as a cementitious component enhancing the binding. Lime

increases the pH of the block and enables the formation of insoluble metal hydroxides.

Chromium level in plating sludge (10.71 mg l1) was reduced to 0.3782 mg l1 after

solidification using binders

Results of the MTCLP test:

Figure 1 Concentration of chromium by multiple toxixity characteristic leaching

procedure test


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The cumulative leaching of chromium was found in the range 2.693.06 mg l1, which is

considerably lower than the TCLP regulatory limits. Yang and Kao20 have reported that

solidification of electroplating sludge using cement and calcium carbonate sludge has

reduced the cumulative leaching of zinc from 2.83 to 0.034 wt% and cumulative leaching of

cadmium from 18.85 to 0.4 wt%. This indicates that even after subjecting the S/S blocks to

rigorous leaching conditions, the stabilized systems exhibit good binding ability for

chromium and can be considered chemically durable.

Results of the ANS test:

Solidified samples were tested according to the American Nuclear Society leaching test

procedure, and the results are presented in Figure 2.

Figure 2 Cumulative fraction of chromium leached from stabilized system as a function

of square root of time

Cumulative fraction of chromium leached (CFL) versus time1/2 over a selected range of

leaching data shows linearity which proved that the transport mechanism of chromium from

solidified sample by the leaching liquid is controlled by diffusion. The values ofDe and LI

derived are presented in Table 3.


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Table 3 Diffusion coefficient and leachability index of chromium by ANS test

The LI values obtained were > 15 for the systems studied, indicating high chromium fixation

by the binders investigated. Value ofDe = 105 cm2/s shows very high mobility or rapid

diffusion andDe = 1015 cm2/s indicates immobility or very slow diffusion. It could be seen

from the table that the LI values range from 16.6 to 17.0 for the mix formulation studied,

indicating high chromium fixation. Chan et al[7] have reported LI values for heavy metals,

viz. Zn, Cr, Pb, Cu and Fe ranging from 7.6 to 9.1 and from 8.3 to 9.5 in cement and cement-

activated carbon matrix respectively.

CONCLUSION

Four different kinds of binder materials, Portland cement, fly ash, lime and gypsum were

tried for solidification of a synthetic metal containing waste. The stability of the solidified

blocks was tested using different leaching tests such as TCLP, MTCLP and ANS 16.1. It was

observed that the chromium leaching out was below the TCLP and US NRC limits. CFL

versus time1/2 over a selected range of leaching data shows linearity, which proved that the

transport mechanism of chromium from solidified sample by the leaching liquid is controlled

by diffusion.

REFERENCES

[1] Conner, J. R., Chemical Fixation and Solidification of Hazardous Wastes, Van Nostrand

Reinhold, NY, 1990, p. 692.[2] Zhang, J. and Bishop, P. L., Stabilization/solidification (S/S) of mercury-containing

wastes using reactivated carbon and Portland cement.J. Hazard. Mater, 2002, 92, 199212.

[3] Savvides, C., Papadopoulos, A., Haralambous, K. J. and Loizidou, M., Cement-based

stabilization/solidification of metal plating industry sludge. J. Environ. Sci. Health, 2001,

A36, 11291134.


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[4] Tommaseo, C. E. and Kersten, M., Aqueous solubility diagrams for cementitious waste

stabilization systems. 3. Mechanism of zinc immobilization by calcium silicate hydrate.

Environ. Sci. Technol., 2002, 36, 29192925.

[5] Catalan, L. J. J., Merlire, E. and Chezick, C., Study of the physical and chemical

mechanisms influencing the long-term environmental stability of natrojarosite waste treated

by stabilization/ solidification.J. Hazard. Mater, 2002, 94, 6388.

[6] Wang, Y. M., Chen, T. C., Yeh, K. J. and Shue, M. F., Stabilization of an elevated heavy

metal contaminated site,J. Hazard.Mater, 2001, 88, 6374.

[7] Chan, Y. M., Agamuthu, P. and Mahalingam, R., Solidification and stabilization of

asbestos waste from an automobile brake manufacturing facility-using cement. J. Hazard.

Mater, 2000, B77, 209226.


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Stabilization/solidification of hazardous and radioactive wastes with alkali

activated cements

ABSTRACT

This paper reviews progresses on the use of alkali-activated cements for

stabilization/solidification of hazardous and radioactive wastes. Alkali activated cements

consist of an alkaline activator and cementing components, such as blast furnace slag, coal

fly ash, phosphorus slag, steel slag, metakaolin, etc., or a combination of two or more of

them. Properly designed alkali-activated cements can exhibit both higher early and later

strengths than conventional portland cement. The main hydration product of alkali-activated

cements is calcium silicate hydrate (C S H) with low Ca/Si ratios or aluminosilicate gel at

room temperature; C S H, tobmorite, xonotlite and/or zeolites under hydrothermal condition,

no metastable crystalline compounds such as Ca(OH)2 and calcium sulphoaluminates exist.

Alkali-activated cements also exhibit excellent resistance to corrosive environments. The

leachability of contaminants from alkali-activated cement stabilized hazardous and

radioactive wastes is lower than that from hardened portland cement stabilized wastes. From

all these aspects, it is concluded that alkali-activated cements are better matrix for

solidification/stabilization of hazardous and radioactive wastes than Portland cement. In later

1957, Glukhovsky first discovered the possibility of producing binders using solutions of

alkali metal and a low basic calcium or calcium-free aluminosilicate (clays) [5]. He called the

binders soil cements and the corresponding concretes soil silicates. Depending on the

composition of starting materials, the binders can be divided into two groups: (a) alkaline

earth alkali binding system Me2OMeOMe2O3SiO2H2Oand (b) alkaline binding system

Me2OMeOMe2O3SiO2H2O. Alkali-activated blast furnace slag cement is a typical

example for the first group and alkali-activated metakaolin or fly ash cement for the second

group.


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STRUCTURAL CHARACTERISTICS OF ALKALI-ACTIVATED CEMENTS

Two important characteristic attracted attentions to alkaline activated cements as host phase

for radiation waste: (i) these materials are set at low temperature (10100C) to give

amorphous of semi-crystalline structure, (ii) the product material have some properties

superior to cement Portland as chemistry stabilized from acid medium.

ME2OMEOME2O3SIO2H2O SYSTEM

The main hydration product of alkali-activated slag cement is calcium silicate hydrate (C S

H) with a low Ca/Si ratio, and Ca(OH)2 exists. According with RMN MAS techniques the

model proposes was based on formation of disordered calcium silica hydrate with a

deierketten structure, in witch tetrahedral lineal chains of silicate (Q1 chain end and Q2

units) are linked to CaO layer. In these structures, association of three members units forms

tetrahedral chains, two tetrahedral bound to the CaO layer and the third one called bridging

tetrahedron, pointing out of the layer. An important part of bridging tetrahedral are occupied

by aluminum tetrahedral (AlT) as Q2(1Al) units. It is found that when the slag fineness,

nature and dosage of alkaline activator, and curing temperature change, the Ca/Si ratio of C S

H, amount of Al incorporated and the chain means length change very little. The minor

hydration products also vary with the characteristics of the raw materials used. Thus, alkali-

activated slag cements show much better resistance in aggressive environments than Portland

cement.

ME2OME2O3SIO2H2O SYSTEM

The main hydration product of alkaline binding system Me2OMe2O3SiO2H2O is

semicrystalline aluminosilicate gel, which is essentially amorphous to X-rays but NMR

studies have revealed a three-dimensional short-range structure in which the Si is found in a

variety of environments, with a predominance of Q4(3Al) andQ4(2Al) units. The

characteristics of the aluminosilicate used, the nature and concentration of activators, and the

curing temperature have the most significant effects on the SiO2/Al2O3 ratio of the hydration

products. It is noticed that alkali-activated fly ash cement has quite different microstructures

when different alkaline activator are used. The OH ion catalyzes the reaction, whereas the

alkaline metal (Na+) and the other ions present in the alkali activator are structure-forming


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elements. N A S H contains tetrahedral Si and Al in its structure, randomly distributed along

the crosslinked polymeric chains; the gaps so formed are large enough to house the charge-

balancing hydrated sodium ions.

RESISTANCE TO CORROSIVE ENVIRONMENTS

Many publications have reported that alkali-activated cements have a much better resistance

to corrosive environments than Portland cement. Figs. 2 and 3 show the corroded depth of

alkali-activated slag and Portland cement pastes with time in pH3 nitric and acetic acid

solutions. Alkali-activated slag cement showed much less corroded depths than the Portland

cement pastes. After 580 days of immersion in pH3 nitric acid solutions, the Portland cement

pastes were corroded approximately 2.5 mm, while the alkali-activated slag cement pastes

were corroded only about 1.3 mm. High aluminum cement is well known for its good

resistance to acid corrosion. Alkali-activated cement can even show much better corrosion

resistance in HCl and H2SO4 solutions than high aluminum cement.

Figure 2 Corrosion Of Cement Pastes In Ph3 Acetic Acid Solution


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Figure 3 Corrosion of cement pastes in pH3 acetic acid solution

It appears that acetic acid is much more aggressive than nitric acid the difference in acid

corrosion resistance became more obvious. After 60 days of immersion, 15mmof Portland

cement and but only 5mm of alkali-activated slag cement pastes were corroded. This is

further confirmed by Bakharev et al. However, it has been reported that, at the same

concentration, mineral acids are more corrosive to hardened cement pastes than weak acids.

The contradiction can be attributed to the different testing conditionsconstant pH was used

in this study and a constant concentration was used by Pavlik.

STABILIZATION/SOLIDIFICATION OF RADIOACTIVE WASTES WITH

ALKALI-ACTIVATED CEMENTS

Radioactive wastes are generated in most nuclear fuel cycle processes, in some other

industries such as hospitals, research facilities, etc. According to the IAEA classification

most of these wastes can be classified as low-level wastes (LLW) or intermediate level

wastes (ILW). Stabilization/solidification has been widely used to treat LLW and ILW. The

leaching resistance of treated products is dependent on the characteristics of the matrix

binder, contaminant being leached and leaching environment.

STABILIZATION/SOLIDIFICATION OF RADIOACTIVE WASTES IN ALKALI-

ACTIVATED SLAG CEMENTS

Cs is the most difficult radionuclide to be stabilized in radioactive wastes. Several laboratory

studies have confirmed that the cesium leachability from alkali-activated slag pastes is much


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lower that that from Portland cement pastes. To evaluate the leachability of Cs+ in alkali-

activated slag cements, monolithic specimens were suspended in deionized water in Teflon

containers at testing temperature, were transferred to other containers with fresh deionized

water at specified intervals, and the concentration of Cs+ in original solutions was measured.

Figure 4 Leached fraction of Cs+in hardened and alkali-activated slag cement pastes

a) Portland cement pastes b) Alkali-activated slag cement pastes

The leached fraction of Cs+ in Portland cement and alkali-activated slag cement pastes

containing 0.5% CsNO3 after 28 days of moist curing at 25 C. The results indicate that the

Cs+ in Portland cement pastes shows much higher leached fraction than that in alkali-

activated slag cement pastes at the same temperature. As the temperature increases from 25

to 70C, the leached fraction of Cs+ in both pastes escalates. The leached fraction of Cs+ in

Portland cement pastes at 25C is even higher than that from alkali-activated slag cement

pastes at 70C. The calculation using Arrhenius equation indicated that the Cs+ leaching

activation energy of Portland cement pastes is 19 kJ/mol compared with 25 kJ/mol for alkali-

activated slag cement pastes. The lower leached fraction and higher leaching activation

energy of Cs+ in alkali-activated slag cement pastes than in Portland cement pastes can be

attributed to the less porous structure and lower C/S ratio in C S H.

STABILIZATION/SOLIDIFICATION OF RADIOACTIVE WASTES IN ALKALI-

ACTIVATED FLY ASH CEMENT

The presence of CsNO3 or Cs(OH)H2O in the alkali activated fly ash cement pastes,

prepared using 8M NaOH solution as activator, showed no significant adverse effects on

mechanical strength or microstructure. Leaching tests following


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TCLP and ANSI/ANS 16.1 indicated that the leachability of Cs in the solidified waste form

is also very low. Microstructural analysis shows Cs associated with the main reaction product

in the AAFA suggesting that cesium is chemically bound rather than physically encapsulated.

It is proposed that cesium is incorporated into the alkaline aluminosilicate gel, a precursor for

zeolite formation.

Figure 5 TEM Picture

CONCLUSION

Alkali-activated cements usually exhibit higher shrinkage than Portland cement when they

hydrate at room temperatures, which may result in the cracking of monolithic waste forms.

Some alkalis may leach out of the waste forms and enter into the environment if they are

immersed in solution. Although the hydration and microstructure development mechanisms

of alkali-activated cements are still not clear, it will be very helpful to establish the

relationship between the nature of contaminants to be fixed and the nature of raw materials

used in the alkali activated cements.


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REFERENCES

[1] C. Shi, R.L. Day, X. Wu, M. Tang, Uptake of metal ions by autoclaved cement pastes, in:

Proceedings of Materials Research Society, vol. 245, Materials Research Society, Boston,

1992, pp. 141149.

[2] C. Shi, X. Shen, X. Wu, M. Tang, Immobilization of radioactive wastes with portland and

alkali-slag cement pastes, Il Cemento 91 (1994) 97 108.

[3] USEPA, Technology Resource DocumentSolidification/Stabilization and Its

Application to Waste Materials, USEPA, June 1993 (EPA/530/R- 93/012).

[4] USEPA, Innovative Treatment Technologies: Annual Status Report, eighth ed.,

November 1996 (EPA/542/R-96/010).

[5] V.D. Glukhovsky, Soil Silicate Articles and Constructions (Gruntosilikatnye virobi i

konstruktsiii), Budivelnik Publisher, Kiev, 1967.


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USE OF ARSENIC CONTAMINATED SLUDGE IN MAKING

ORNAMENTAL BRICKS

H. M. A. Mahzuz; R. Alam; M. N. Alam; R. Basak; M. S. Islam

ABSTRACT

Arsenic contaminated sludge can be substantially found from the treatment of arsenic

contaminated ground water. Lake of proper management and reuse of this sludge can create

further environmental problem as there is probability of mixing with soil and water. In this

paper, effort is taken in order to use of such waste. Here, effectiveness of using this sludge

during the process of making ornamental brick has been analyzed and justified. The detailed

study was made upon the suitability of sludge in making bricks. Results of different tests

indicate that sludge proportion is the key factor for determining the quality of ornamental

bricks/tiles. The compressive strength of ornamental bricks mutually decreases with increase

of sludge proportion. This study showed that arsenic contaminated sludge could be used

safely up to 4 % for making ornamental bricks. Because upper than this limit, the quality of

bricks or tiles may be fallen considerably.

USE OF ARSENIC

Arsenic has found widespread use in agriculture and industry to control a variety of insect

and fungicidal pests (Leist et al., 2000). Arsenic tri-oxide is used in manufacturing of

agricultural chemicals (pesticides), glass and glassware, industrial chemicals, copper and lead

alloys and pharmaceuticals. In agriculture, arsenic compounds such as lead arsenate, copper

aceto arsenite, sodium arsenate, calcium arsenate and organic arsenic compounds are used as

pesticides. Substantial amount of methyl arsenic acid and diethyl arsenic acid are used as

selective herbicides. Chromate copper arsenate, sodium arsenate and zinc arsenate are used

as wood preservatives. Some phenyl arsenic compounds such as arsenal acid are used as feed

additives for poultry and wine. Small amount of arsenic compounds continue to be used as

drugs in some countries. As medicine arsenic is used since the fifth century BC, when

hypocrites recommended the use of an arsenic sulfide for the treatment of abscess. Arsenic

preparation was used for the treatment of skin disorder, tuberculosis, leukemia, asthma,


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leprosy, syphilis, amoebic dysentery, etc. Homeopaths are also using arsenic as drug.

Besides, arsenic is used in the preparation at dyes, poisonous gas and transistor, as a

component of semiconductor, as a preservative in tanning and in the industry of textile and

paper, etc. (Dhaka University Hospital, 2003). After treating, the arsenic contaminated water

sludge of arsenic-iron is produced. In another study, it was found that the recommended

proportion of this contaminated sludge in brick making is up to 15 %-25 % by weight. (Rouf

and Hossain, 2003) Arsenic contaminated groundwater is used extensively in Bangladesh to

irrigate the staple food of the region and paddy rice (Oryza sativa L.). To determine whether

this irrigation is good for environment or not, a survey on arsenic levels in paddy oils and

rice grain was undertaken. It showed that arsenic levels were elevated in zones where arsenic

in groundwater used for irrigation was high and where these tube-wells have been in

operation for the longest parkperiod of time. (Meharg and Rahman, 2002). The total arsenic

content of 150 paddy rice samples were collected from Barisal, Comilla, Dinajpur, Kaunia

and Rajshahi districts of Bangladesh. It was found that arsenic concentrations varied from 10

to 420 g/kg at 14 % moisture content. Rice yields and grain arsenic concentrations were 1.5

times higher in the boro (winter) than the monsoon (summer) season, consistent with the

much greater use of groundwater for irrigation in the boro season. Mean values for the boro

(winter) and aman season (monsoon rices) were 183 and 117 g/kg, respectively (Duxbury et

al., 2003).

OBJECTIVE OF THE RESEARCH

Keeping the above factors in mind, the research work was carried to use this contaminated

sludge in making a product, which has some economic values. Therefore, it will definitely

reduce the pollution of surface water, ground water and the environment from uncontrolled

disposal of arsenic-iron contaminated sludge.

ORNAMENTAL BRICK

Ornamental bricks are special types of bricks. These are used for decorative work. Real estate

companies use ornamental bricks according to the requirements of customer. Different types

of ornamental bricks, which are made in the Khadim Ceramic Industry for this research

purpose.


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Figure 1 Different types of ornamental blocks

MATERIALS AND METHODS

The raw material (arsenic sludge) used for this study was collected from arsenic- iron

removal plant (AIRP) of Manikganj sadar of Manikganj District near the pourashava office

(Fig. 2). Then the basic physicochemical characteristics were examined. It includes

determination of moisture content and pH. Heavy metal content, i.e. the concentration of

arsenic and iron (Table 2) was determined by acid digestion with a HNO3: HCl volume of

ratio of 1:3 (aqua- regia). Mortar in cube 6 shape is a measure to get compressive strength.

The mortar used in manufacturing of cube is the mixture of cement, sand and water with a

ratio of 1: 2.75: 0.485. In the work, various proportion of oven dried sludge (0.5 %, 1.0 %,

1.5 %, 2.0 %. 2.5 %) were mixed with sand by basis weight. But total proportion of sand in

manufacturing ratio of concrete was not changed. After 24 h, the moulds were stripped off

and the cubes are further cured in water for 7 days. After 7 days, the cubes were tested to


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check the crushing strength. Three cubes of each proportion of sludge were made and took

the average of crushing/compressive strength value. Three standard cube samples were also

made without using contaminated sludge, only with cement, sand and water maintaining the

same ratio of 1: 2.75: 0.485. They were made following the same procedure. Compressive

strength of these cubes was also measured for comparison of compressive strength. The clay

sample for ornamental bricks was collected from Khadim ceramic limited (KCL) located at

Khadim Nagar in Sylhet. At first, various proportion of sludge was mixed with clay soil on

basis weight (2 %, 4 %, 5 %, 6 %, 8 % and 16 %) and clay was prepared in batches (3

samples for each proportion). After complete mixing, the clay soil was taken to the brick

manufacturing machine. In this research, four types of ornamental bricks e. g. Tapper tiles,

Dulpori, CT- 5 and 1" 6" are studied. All the ornamental bricks are produced following the

standard rule of KCL. Again, standard samples of those four types of ornamental bricks were

also made. The ornamental bricks were then tested for compressive strength. Three bricks of

each proportion of sludge were tested and took the average crushing/compressive strength

value. This was done to compare the compressive strength of ornamental bricks which have

different sludge proportions with the standard ornamental bricks to identify the safe

numerical percent value for practical use.

RESULTS AND DISCUSSION

Sand property analysis

For concrete sand, FM range is 2.3-3.1 (Mobasher, 1999). The sand used in making the cubes

was subjected to different experimental procedures, which gives the unique values to define

the sand to a specified category. Table 1 represents the various physical properties of Sylhet

sand.

Table 1 Physical properties of naturally iron-rich sylher sand


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Sludge property analysis

The specified physicochemical properties associated with the suitability of sludge in use of

manufacturing of ornamental bricks were determined and the findings are represented in

Table 2.

Table 2 Physicochemical properties of arsenic-iron contaminated sludge

Density of ornamental bricks

The density of ornamental bricks decreases with the increase of sludge addition. Table 3

shows the comparison between the densities of ornamental bricks made without sludge and

those made using different proportion of sludge. From the figures, it can be concluded that up

to 4% sludge addition, the density of ornamental bricks is not much affected. But when

sludge addition is more than 4%, then the quality of ornamental bricks may be affected.

Table 3 Comparison of density(gm/cm3)

Firing shrinkage of ornamental bricks

Shrinkage during firing is unavoidable. The quality of brick can be assured according to the

degree of firing shrinkage. From the data analysis, it is seen that the percentage of shrinkage

increases as the amount proportion of up to 4 %, the firing shrinkage of ornamental bricks is

below the bricks made without sludge. But it increases when sludge addition is more than

4%.


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Table 4 Comparison of firing shrinkage (%)

Results from compressive strength test of mortar:

Table 5 Compressive strength of cubes

Table 6 Comparison of compressive strength (psi)

Presence of arsenic (V) reduces the initial and final settling time of cement. Again,

compressive strength of cement increases with increase of arsenic (V) content (Minocha andBhatnagar, 2007). In this study, cubes made using the arsenic contaminated sludge were

tested for compressive strength. From Table 5, it is clear that desired strength was not found

when sludge was mixed with clay soil in the manufacture of cubes. Even at small proportion

of sludge mixing the compressive strength of the cubes can be hampered. Therefore, it can be

concluded that sludge mixing is not recommended in the manufacturing of mortar. From the


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Table 6, it was seen that up to 4% of sludge addition, compressive strength of the ornamental

bricks made using sludge, is always as high as that of ornamental bricks made without

sludge. The compressive strength of the ornamental bricks made using sludge lost their

quality with the addition of more than 4 % of sludge. Thus, the maximum of 4 % of sludge

can be mixed as clay material safely.

CONCLUSION

This work tries to demonstrate a feasible way of using arsenic contaminated sludge as a clay

substitute to produce quality ornamental bricks. Different measurements of both clay- sludge

mixture and cube and ornamental bricks were carried out to evaluate the factors that could

affect the ornamental brick quality. The results of compressive strength tests on the cube

shows that desired strength can not be found in cubes when they were manufactured of cubes

done using arsenic contaminated sludge, even when just 0.5% sludge was substituted as sand.

Based on the results of compressive strength of cube, it can be said that Arsenic sludge is not

suitable as raw material in manufacturing of mortar in cube shape.

Use of waste as an aggregate on mortar may be an effective management option. But the

required strength value must be maintained. For example, the utilization of waste glass in

concrete can cause cracking and weakening due to expansion by alkali silica reaction (Park

and Lee, 2004). Compressive strength of mortar increases with an increase in cement content

and decreases with an increase lime, sand, water or air content (Masonry Advisory Council,

2008). The results of compressive strength tests on the ornamental bricks indicate that the

strength is greatly dependent on the amount of sludge substituted as clay soil. The optimum

amount of sludge that could be mixed with clay to produce good bonding of ornamental

bricks was 4 % (safely maximum) by weight. On the other hand, if 4 % of sludge is mixed to

the clay soil, the firing shrinkage of the ornamental bricks would not be affected. But the

firing shrinkage starts to vary with the addition of more than 4 % sludge by weight. Totally,

the recommended proportion of sludge in ornamental brick making is 4 % by weight to

produce a good quality ornamental brick using arsenic contaminated sludge.


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REFERENCES

[1] Akhtar, H.; Cartledge, F. K.; Miller, J.; Melearn, M., (2000). Treatment of arsenic-

contaminated soils, soil characterization. J. Environ. Eng., 126 (11), 999-1003 (5 pages).

[2] Alam, M. G. M.; Allinson, G.; Stagnitti, F.; Tanaka, A.; Westbrooke, M., (2002). Arsenic

contamination in Bangladesh groundwater: A major environmental and social disaster. Int. J.

Environ. Heal. R., 12 (3), 235-253 (19 pages).

[3] Artiola, J. F; Zabeik, D.; Jhonson, S. H., (1990). In situ treatment of arsenic contaminated

soil from a hazardous industrial site: Laborator studies, solidification or stabilization. Waste

Manage. 10 (1), 73-78 (6 pages).

[4] Basak, R.; Islam, M. S., (2008). A study on the use of arseniciron contaminated sludge in

making construction materials. B.Sc. thesis, Department of Civil and Environmental

Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh, 1-2. De,

A. K., (1994). Environmental Chemistry, 3rd. Ed., New Age International (P) Limited

Publishers, New Delhi-110 002, ISBN: 81-224-0648-3, 78-80.

Solidification and Stabilization

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