Indian Geotechnical Conference (December 18-20, 2003) s1

Remediation of Hazardous Solid Waste from Titanium Industries IGC 2009, Guntur, INDIA

REMEDIATION OF HAZARDOUS SOLID WASTE FROM TITANIUM INDUSTRIES

P.K. Jayasree Senior Lecturer in Civil Engineering, College of Engineering, Trivandrum, Kerala, India. E-mail: [email protected] Y. Sheela Evangeline Assistant Professor in Civil Engineering, College of Engineering, Trivandrum, Kerala, India. E-mail: [email protected] K.J. Sudhir Lecturer in Civil Engineering, SN Polytechnic College, Kottiyam, Kollam, Kerala, India. E-mail: [email protected]

ABSTRACT: Electrokinetic remediation method is a viable method for heavy metal removal which is based on the principle that when direct current is passed through contaminated soil, certain types of contaminants (negatively charged) will migrate through the soil pore water to a place where they can be removed. In this work, an attempt has been made to study the viability of using electrokinetic remediation in decontaminating the hazardous solid sludge waste from titanium industries. Minerolgical, chemical and physical properties of the same were determined in order to characterise the waste according to Indian Standards. Experiments were conducted by varying the electrolytes to understand the efficiency of enhancing solutions. Concentration of unwanted heavy metals viz., Pb, Cr (VI), Cu, Mn, and Zn were determined before and after the remediation studies to prove the efficiency of the method.

1. INTRODUCTION 1.2 Electrokinetic Remediation 1.1 General Electrokinetic remediation is an emerging in-situ or ex-situ technology for the remediation of contaminated sludge Our surroundings get polluted at a rapid rate by the brisk having heavy metals. A low level direct current in the order industrialisation and other human activities. The hazardous of few Volts/cm is applied across electrode pairs, which are waste from industrial activities, when not managed properly placed in the electrode compartments. Electric current causes has been creating problems for human health and environment, electromigration, electroosmosis and electrophoresis, which since the day of commencement of industrialisation. Some of result in the movement of contaminants to their respective the industrial wastes have been proved to be extremely toxic. electrodes. The application of this method in the removal of In Kerala, there are 423 hazardous waste generating units as heavy metals from contaminated soils have been proved by a per the records of Kerala State Pollution Control Board number of researchers like Reddy & Chinthamreddy (2003), (KSPCB). Kerala Minerals and Metals Ltd (KMML) Sheela et al. (2008), Yeung & Hsu (2005), Yeung et al. commissioned in 1985, is one such industry creating (1996) etc., to name a few. hazardous waste, located at Chavara in the coastal areas of Here in this study an attempt is made to determine the index, Kollam District in Kerala. engineering, chemical and mineralogical properties of the dry KMML produces 48,000 MT/year of titanium dioxide sludge waste and to check the viability of electrokinetic pigment from raw illmenite which is beneficiated at their remediation in the decontamination of waste. Electrokinetics plant. At the same time, 40,000 MT/year of contaminated is undertaken by using potable water as purging solution in sludge having heavy metals is created and is permanently the baseline study of unenhanced condition and with EDTA stored in huge tanks. Such disposal of waste is not a (ethylene diamine tetra acetic acid) in the enhanced sustainable solution in the long term because of the security remediation. problem and limited availability of land space. Spreading of this heavy metal contaminated waste through any medium, 2. CHARACTERISATION OF SLUDGE WASTE not only affects the public health but also alter physical, Sludge samples were collected from the storage tank of chemical and biological properties of the original soil. KMML in plastic bags and separated out for moisture

40 Remediation of Hazardous Solid Waste from Titanium Industries content determination and electrokinetic remediation process. 2.1 Presence of Heavy Metals The remaining samples were dried and stored in gunny bags. The sludge waste samples from the KMML were subjected Index properties of the sludge waste were determined to to Atomic Absorption Spectroscopy (AAS) and heavy metals classify the materials as per Indian Standards and are shown such as Cd, Cr+6, Cu, Fe, Mn, Zn and Pb were found in the in Table 1. From these properties, it can be seen that sludge. All of the heavy metals pose health hazard to the according to Indian standards, sludge can be classified as fine public. Results obtained are tabulated in Table 3 along with grained, highly compressible, organic silt of low plasticity permissible limits hazardous limit in solid waste as (OH). The present study is mainly aimed to check the prescribed by KSPCB (2008) and Government of India viability of reuse of the sludge waste as a fill material. So (1989, 2003). engineering properties like optimum moisture content, maximum dry density and unconfined compressive strength From the AAS test results of KMML sludge, it can be noted were also determined and are listed in Table 1. The that concentrations of all heavy metals are above the standard engineering properties indicate that the sludge waste is soft limits as compared with drinking water parameters. But in nature and it can be very easily deformed by squeezing. when compared to limits of hazardous waste concentration, two parameters were found to be above the prescribed limit. Table 1: Index and Engineering Properties of KMML Sludge Substantial amount of Cr+6 is present in it, which is twelve Properties Values times greater than the limit. Concentration of iron is also seen to be above the prescribed limits. As per KSPCB’s Sand 12% Hazardous Wastes Rules (2008), Hazardous Wastes Silt 76% (Management and Handling) Rules, Government of India Clay 12% (1989 and 2003), exceeding of the limits by even a single Liquid limit 64% parameter, it will be under the category of Hazardous sludge. Plastic limit 41% Because of this reason, KSPCB has declined permission to Plasticity Index 23% KMML to shift this sludge from the factory premises. So Natural moisture content 14% shifting is possible only after proper remediation of the Specific gravity 1.88 sludge. This substantiates the need for electrokinetic IS Classification OH remediation of the waste sludge from KMML. Optimum moisture content 35% Maximum dry density 8.25 k N/m3 Table 3: Heavy Metals in Sludge with Concentration Limits Unconfined comp. 45.29 kPa strength Heavy Concentration in Concentration metals KMML sludge (ppm) limits (ppm) The chemical and mineralogical properties were also Cd 3.20 50 determined and are tabulated in Table 2. Although the Cr+6 595.24 50 presence of chemicals like Nitrogen, Phosphorous and Cu 26.80 5000 Potassium were found to be in small quantities, organic Fe 151559.00 50000 content in the sludge was obtained as 62%. This high organic Mn 1246.00 50000 content may be due to the presence of raw materials such as Ni 112.30 5000 petroleum coke, calcined petroleum coke etc. used for the Pb 101.40 5000 manufacture of titanium dioxide. The pH value obtained Zn 1854.00 20000 indicates the alkaline nature of the sludge waste. The cation exchange capacity value shows the capacity of the sludge for ion exchange of cations between the sludge and the pore 3. ELECTROKINETIC REMEDIATION TEST water in the sludge. The study of sludge waste was also 3.1 Testing Procedure subjected to X-ray diffraction analysis and it was obtained that the predominant minerals in the sludge are gibbsite and Decontamination studies were done on the samples using gaulrite. The scanning electron microscopy views of the electrokinetic remediation method. For this, samples were sludge show a porous nature. placed in a specially fabricated electrokinetic cell of size 21 cm × 15 cm × 15 cm attached to two electrode compartments Table 2: Chemical and Mineralogical Properties and reservoir. Each electrode compartment was of 15 cm × 5 cm Properties Values × 15 cm in size. The partition wall between the sludge and Organic content 62% electrolyte compartments had lot of small holes for the inter CEC 15.5meq/100 gm soil connection. To prevent the mixing of sludge in to the electrode pH 7.2 compartments, these holes were covered with filter paper. N 1.1% Sludge having moisture content same as in the field P 0.02% condition was tamped uniformly in to the electrokinetic cell K 0.012% using a hand compactor in three different layers, so that the

41 Remediation of Hazardous Solid Waste from Titanium Industries amount of void space was minimized. The anode and cathode depends on the relative efficiency of the two transport compartment were filled with potable water in the mechanisms. When the electroosmotic flow direction is unenhanced study. Potable water was selected because it is reversed, the migration of EDTA ions toward the anode by the most probable and economic source of replenishing fluid ionic migration is enhanced by electro-osmotic advection. at a field contaminated site. The electrokinetic cell was then connected to the power supply and required constant voltage 4. RESULTS AND DISCUSSION of 26 V (i.e. at the rate of 1V/cm) was applied because the distance between the graphite electrodes used in this 4.1 Current Consumption experiment was 26 cm. The electrokinetic arrangement is Consumption of current is an important factor in shown in Figure 1. The electric current across the soil sample electrokinetic remediation. Figure 2 shows the utilisation of under constant voltage was measured at different time the electrical current utilised during the Electrokinetic test. periods using an ammeter. The electrolytes from respective The current primarily results from the electro migration of compartments were removed and replaced one at a time ions through the pore fluid and the current density is an when there is a fall in the current consumption. This will indication of the amount of ion electromigration that is ensure that the contaminant that migrated in to these occurring. In the test using potable water, the current reached electrode compartments did not diffuse back in to the soil. a value of 16 mA immediately after the starting of the test Experiments were continued till current requirement was and then reached a peak of 44 mA after 14 Hrs, and then stable. i.e., the current stabilisation was considered as the decreased and stabilised to 5 mA after 23 Hrs. When EDTA terminating factor. was used as chelating agent (purging solution), current consumption at the commencement of the test was 18 mA, then increased to 53 mA in 23 hours and then goes down. Here steady current of 4 mA reached after 35 Hrs. i.e. the stabilisation of current consumption was considered as the terminating factor. In this test, it was theorised that the presence of NaOH would help to increase the electrical conductivity of the pore solution and generate a more sustained electrical current. This study shows that the current utilisation was of the order of few mA and hence it is very economical in the current consumption point of view.

60 With Water With EDTA A. Anode reservoir B. Overflow tank 50 A m

C. Graphite electrodes D. Contaminated sludge 40 n i

E. Multimeter F. AC supply t 30 n

G. Automatic transformer H. Converter e r

r 20 Fig. 1: Schematic Sketch of Electrokinetic Setup u C 10 In the enhanced study, the cathode well was filled with 0.2M 0 EDTA (Ethylene Diamine Tetra Acetic acid) as chelating 0 20 40 60 agent and the anode with 0.5M NaOH (Sodium hydroxide) to Time in Hours increase the pH simultaneously. EDTA is a strong chelating Fig. 2: Consumption of Current During Electrokinetic agent that forms strong 1:1 complexes with heavy metals. Process For example, as indicated by Yeung & Hsu (2005), EDTA forms a strong complex with cadmium, whose logarithmic 4.2 Heavy Metals in Sludge after Electrokinetics value of the formation constant is 16.4 (Dean 1992). The high value of the formation constant indicates the chemical In order to understand the heavy metal concentration on the stability of the soluble complex and the high potential of wastes after electrokinetic remediation, atomic absorption EDTA in enhancing the removal of cadmium from spectroscopy (AAS) studies were conducted on the samples. contaminated soils. Yeung et al. (1996), and Reddy & AAS is a technique for determining the concentration of a Chinthamreddy (2003) give more detailed descriptions of the particular metal element in a sample. To understand the properties of EDTA and the mechanisms of heavy metal– potential of the electrokinetics, all the five metals that are EDTA complexation. EDTA and its metal complexes are identified in the sludge before remediation were again tested negatively charged. When a forward electro-osmotic flow for AAS after remediation. To know the variation of heavy prevails, i.e., from anode toward cathode, the EDTA ions are metal removal after remediation, along the sludge in the moved toward the anode by ionic migration and toward the electrokinetic cell, samples were taken from three one very cathode by electro-osmotic advection. The net migration near to the cathode, another very near to the anode and the

42 Remediation of Hazardous Solid Waste from Titanium Industries third at the centre. Thus total six samples, three from concentrations of soluble salts or presence of organic particle unenhanced and three from enhanced remediation studies (62% in KMML sludge) reduce the solubility of the heavy were used for the AAS study. metals and convert them in to suspended particles leads to reduction of removal. As seen from Table 3, concentrations Figure 3 shows the percentage removal of cadmium, copper, of iron and chromium exceed the limits prescribed by the chromium and iron from the waste after electrokinetic hazardous waste rules (1989, 2003 and 2008). For these remediation without purging solution. Figure 4 shows the heavy metals addition of EDTA has brought the removal results of the same when enhanced with a purging solution. efficiency to the range 57–71% and 21–55% respectively. Despite a very efficient clean up of the specimen, there was Figures 5 and 6 show the effect of percentage removal of no significant migration of the same into the anode well. In manganese, nickel, lead and zinc with and without purging the case of chromium and iron, migration of ions towards the solution respectively. Migration of nickel and manganese anode is more while for copper it is towards the cathode. were negligible. This may be because these cations were That is the reason for the removal efficiency to be maximum adsorbed or precipitated throughout the soil as a result of the +6 at the cathode for Cr and Fe and at the anode for copper. high pH condition of the sludge. But in the case of lead and zinc, as in copper and iron, maximum removal efficiency is Near Cathode observed at the anode showing the migration of ions towards

a At Centre the cathode. A similar result can be observed in Sheela et al. v o 80 Near Anode 2008. m e

a 40 t n e 20 l 100 Near Cathode c a r v

e At Centre o

P 80 0 Near Anode m e

Cd Cu Cr+6 Fe r 60

Type of heavy metals a 40 t n

e 20 c r Fig. 3: Removal of Cd, Cu, Cr +6 and Fe in Unenhanced e P 0 Study Mn Ni Pb Zn Type of heavy metals Near Cathode

a At Centre v o 80 Near Anode Fig. 5: Removal of Mn, Ni, Pb and Zn in Unenhanced Study m e

a 40 t n

e 20 c l

r 100 Near Cathode a e v P 0 At Centre o 80

Cd Cu Cr+6 Fe m Near Anode e

Type of heavy metals e g

a 40 t n

e 20 c

Fig. 4: Removal of Cd, Cu, Cr +6 and Fe in Enhanced Study r e

P 0 In this study, it is revealed that percentage removal from the Mn Ni Pb Zn centre portion of the electrokinetic cell was found to be low Type of heavy metals as compared to other portions such as near anode and cathode. This may be due to low electrical conductivity and low ionic strength. Zone of low electrical conductivity and Fig. 6: Removal of Mn, Ni, Pb and Zn in Enhanced Study low ionic strength causes the overall electrical resistance of the sample to rise significantly, so that the electric current 5. CONCLUSIONS falls, and also significantly reduces the electric potential gradient in zones where contaminant ions are still present. The following conclusions are deduced from the experimental Another reason may be the formation of clean water at the results: central portion by the action of acid front from the anode  The characterization studies reveal that the KMML meets the alkali front from the cathode; hydroxium and sludge belongs to silt of high compressibility category. hydroxy ions recombine to give water. Also physical or chemical changes in water, like change of pH and

43 Remediation of Hazardous Solid Waste from Titanium Industries

 Heavy metals in KMML sludge such as iron and REFERENCES hexavalent chromium concentration were found to be Dean, J.A., (ed.). (1992). Lange’s Handbook of Chemistry, above the limits specified by the hazardous waste 14th Ed., McGraw-Hill, New York. management rules-2008 of Kerala State Pollution Control Board and Hazardous Wastes (Management and Hazardous Wastes (Management and Handling) Rules, 1989: Handling) Rules, Government of India (1989 and 2003). Department of Environment, Government of India. Hazardous Wastes (Management and Handling) Amendment  Cadmium being in small quantities in the waste, is Rules, 2003: Department of Environment, Government of completely removed after the remediation process. India. +6  The maximum removal efficiency of Fe and Cr from Hazardous Wastes – Management, Handling, Transboundary KMML sludge through enhanced study of electro- Movement Rules, 2008: Guidelines of Kerala State kinetics was found to be 57–71% and 21–55% Pollution Control Board (KSPCB), pp. 33–45. respectively. Reddy, K.R. and Chinthamreddy, S. (2003). “Enhanced  In electrokinetic remediation, enhancement study with Electrokinetic Remediation of Heavy Metals in Low purging solution reveals that EDTA is a good chelating Buffering Clayey Soils”, ASCE Journal of Geotechnical agent. and Geoenvironmental Engineering”, Vol. 129, No. 3,  The potential of the electrokinetic processing for the pp. 263–153. removal of heavy metals from KMML sludge is Sheela, E.Y., Jayasree, P.K, Anima, T.M. and Dhanyatha, confirmed. B.V.G. (2008). “Pilot Studies on the Utilisation of Solid  There are many complicating factors such as electrical Waste from TTPL as a Fill Material”, The 12th conductivity, ionic strength, electrochemical properties International Conference of International Association for of sludge, chemical action of electrode material during Computer Methods and Advances in Geomechanics electrolysis, spacing and inter changing of electrodes, (IACMAG) 1-6 October, 2008, Goa, India, pp. 2365– need and use of intermittent changing of the electrolyte 2371. solution from electrode compartments, etc. will affect Yeung, A.T. and Hsu, C.N. (2005). “Electrokinetic the electrokinetic remediation of multiple heavy metals Remediation of Cadmium-Contaminated Clay”, ASCE in KMML sludge. Journal of Environmental Engineering, Vol. 131, No. 2,  Overall, this study found that many factors influence the pp. 298–304. heavy metal removal during EDTA enhanced Yeung, A.T., Hsu, C. and Menon, R.M. (1996). “EDTA- electrokinetic remediation and all of these factors must Enhanced Electrokinetic Extraction of Lead”, J. Geotech. be carefully evaluated through intensive and focussed Eng., 122(8), 666–673. research to enhance contaminant removal.