Solidification and Stabilization of Fly Ash from Mixed Hazardous Waste Incinerator Using Ordinary Portland Cement

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1 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. 289 MYU Tokyo ES633 Solidification and Stabilization of Fly Ash from Mixed Hazardous Waste Incinerator Using Ordinary Portland Cement Agamuthu Pariatamby *, Chitra Subramaniam, Satoshi Mizutani 1 and Hiroshi Takatsuki 2 Institute of Biological Sciences, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia 1 Osaka City University, Osaka , Japan 2 Ishikawa Prefectural University, Ishikawa , Japan (Received December 2, 2005; accepted May 2, 2006) Key words: fly ash, solidification, stabilization, leaching test, mixed hazardous waste Fly ash samples from a mixed hazardous waste (MHW) incinerator were subjected to solidification and stabilization (S/S) studies using ordinary Portland cement (OPC) as the binder. Additives (i.e., activated carbon and rice husk) were also homogenized with the binder and waste to determine the effectiveness of the immobilization of heavy metals. The toxicity characteristics leaching procedure (TCLP), Japanese Leaching Test (JLT-13) and the American Nuclear Test 16.1 (modified) ANS 16.1 were used to gauge the leaching of heavy metals from the solidified matrixes. Compressibility strength of the solidified matrixes was also tested using the American Standard Testing Material (ASTM) test procedure for the compressive strength of hydraulic cement mortars. 1. Introduction Malaysia's manufacturing sector is rapidly growing, moving from agricultural and primary commodities to industrial output. The downside of this accelerated industrialization is that it results in a considerable amount of solid-waste generation, particularly, hazardous waste of various types. The amounts of hazardous waste generated were 280,000 tonnes in 1984, 380,000 tonnes in 1987, 398,518 tonnes in 1998 and 363,417 tonnes in * agamuthu@um.edu.my Present affiliation: Urban Recycle Engineering, Graduate school of Engineering, Osaka City University 289

2 290 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al (1) Effective techniques for the reduction in the amount of solid and hazardous waste, remediation and elimination have attracted unprecedented interest in recent years. (2) Incineration is fast becoming an important technology in Malaysia s waste management. However ash, which is a by-product of incineration, is normally disposed of in landfills. This could lead to surface and ground water contamination when heavy metals in the ash migrate laterally. (3) This project focused on the treatability of incineration ash by solidification / stabilization (S/S) of the ash using cement. 2. Methods 2.1 Leaching tests TCLP:Toxicity characteristics leaching procedure (TCLP) (4) The TCLP protocol USEPA method 1311 was carried out on the samples after 28 days of curing. An extraction buffer composed of acetic acid and sodium hydroxide of ph 2.88 ± 0.05 was prepared. The ratio of extraction liquid to crushed particles used was 20:1. The leachant was then analyzed for heavy metals in the extract. The results are expressed in terms of the percentage of leachable fraction (f) for each element. This shows the amount of a particular trace metal extracted relative to the amount of the element in untreated ash, which actually shows the availability of metals for leaching from solidified ash over time. f = (q/c) 100 (1) Here, q is the quantity of a certain trace metal detected in the leachate of the S/S ash-cement matrix (mg) and C is the total concentration of this trace metal detected in the untreated ash (mg) JLT-13 : Japanese Leaching Test -Environment Agency Notification No. 13 (5) For this test, an extraction buffer composed of hydrochloric acid and sodium hydroxide of ph 6.00 ± 0.05 was prepared and used at a liquid-to-solid (L/S) ratio of 10:1. The buffer was added to the crushed waste matrices and mechanically shaken continuously for 6 h in an incubator shaker at 200 rpm. After 6 h, the leachate samples were filtered and the ph of and amount of heavy metals in the leachant were analyzed in the same manner as for TCLP. The results were also expressed in terms of the percentage of leachable fraction (f) for each element American Nuclear Society 16.1 (ANS 16.1, modified) This leaching procedure is a simplified and modified method of ANSI/ANS 16.1, the American Nuclear Society for solidified low-level radioactive wastes in standard, which is conducted for 90 days. ANS 16.1 affords more information about the leaching rate of trace metals from the S/S waste-cement matrix than TCLP and JLT-13. The leaching of the samples was performed for 28 days with leachate samplings on the 1st, 3rd, 7th, 14th and 28th days. The trace metals in the leachate were analyzed using inductively coupled plasma atomic emission spectroscopy. The results were recorded in terms of leaching rate (l) and cumulative fraction leached (CFL) relative to the total mass of the waste sample. From these

3 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. 291 results, leachability index (LI) was calculated. LI is an indication of the effectiveness of the S/S method for controling the leaching of trace metals. The larger the LI, the lower the rate of containment diffusion. The calculations were performed using the formulas below. The effective diffusion coefficient (D) is a measure of the diffusibility of the heavy metals of concern in the S/S waste for each leaching interval. (i) Leaching rate, l (cm/day), as a function of leaching time: l = (A n /A o ) [V/(S t n )], (2) where A n is amount of the constituent of interest leached during the interval n (mg/l), A o is the amount of the constituent of interest initially present in the specimen (mg/l), V is the specimen volume (cm 3 ), S is the specimen surface area (cm 2 ) and t n is the leaching time since the start of the first leaching interval (s). (ii) Cumulative fraction leached, CFL (cm): CFL = ( A n /A o ) (V/S) (3) (iii) Effective diffusion coefficient, D (cm 2 /s): D = [(A n /A o ) / ( t) n ] 2 (V/S) 2 T, (4) where t n is t n t (n 1), the duration of the n leaching interval (s). T is [1/2 (t 1/2 n + t 1/2 n 1)] 2, the leaching time representing the cumulative time in the middle of the interval n (s). (iv) Leachability index, LI (dimensionless): LI= 1/n [log ( /Di)]n, (5) where is a constant (1.0 cm 2 /s), n is the number of leaching periods for which analytical results were obtained and Di is the effective diffusivity of constituent i. 2.2 Unconfined compressive strength This test was carried out according to the American Standard Testing Material (ASTM) the test method for the Compressive Strength of Hydraulic Cement Mortars C190/C 109M- 95. The strength of the cubes was measured using a calibrated hand-operated hydraulic compression apparatus (model ELE) on the 7th, 14th and 28th days of curing. The total maximum load was recorded at the point of fracture of the cubes. The load was calculated using fm = P / A, (6) where fm is the compressive strength (MPa), P is the total maximum load (N) and A is the area of loaded surface (mm 2 ).

4 292 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. 3. Results and Discussion The mean particle size of the ash was m. The untreated ash showed a high-ph range of When MHW was subjected to OPC solidification, Cd, Cr, Cu, Fe, Mn and Ni showed higher solubilities (Fig. 1). Almost all of the Cd, Cr and Cu, 20% of Zn and 10% of Pb leached out. The addition of activated carbon (Ac) and rice husk (Rh) resulted in all metals being detected below detection levels. Only Pb leached from the cementsolidified material containing additives. Activated carbon and rice husk added to cement strongly decreased the rate of metal leaching. Ac and Rh adsorbed the heavy metals into the solidified matrix, thus, the concentration of metal that leached out was too low to be detected. However, it was observed that the percentage of leachable fraction decreased as the cement loading increased 40% 70%. JLT-13 exhibited almost similar trends in results for the ash tested using the TCLP method. Almost all of Cr, 70% of Cd and Cu, 5 25% of Pb, and 5% of Zn leached out. The leaching rates as determined by JLT-13 are smaller than those determined by TCLP. When Ac and Rh were added, only Pb leached at values between %. Activated carbon and rice husk added to the cement strongly decreased the rate of metal leaching. In general, from the ANS 16.1 test results, it was observed that the leaching rate of all the metals decreased with time. The leaching rates of only two metals, Cr and Ni, decreased notably for all four sets of cement loads (70%, 60%, 50% and 40%). Based on results of the diffusion leaching test, the leaching of Cr is more pronounced than that of Pb. Leaching rate was found to be highest in the 40% MHW ash load (Fig. 2) followed by those in the 70%, 50% and 60% loads. It was generally seen that all the metals showed increasing cumulative fraction leached (CFL), which corresponded to the square root of leaching time in a linear increase. This shows that the leaching of metals occurred through diffusion. (6) It was also observed that CFL increased notably from the first day to the third day and thereafter increased slightly. The leachability index (LI) values for the MHW solidified with OPC alone and with Ac or Rh were between , and , respectively. It was also observed that the LI values for most of the metals were higher (above 6.0) in the 60%, 50% and 40% ash loads (Fig. 3). This indicates that the metals were retained well within the solidified waste form. (7) The effectiveness of additives for decreasing metal diffusibility was not statistically significant in this study because the MHW solidified with OPC alone and with Ac or Rh exhibited similar results. The compressive strength for MHW solidified with OPC alone was between MPa; for the MHW-Ac-OPC and MHW-Rh-OPC, they were between MPa and MPa, respectively (Fig. 4). The additives reduce the unconfined compressive strength of the MHW solidified waste matrices; however, the reduction was not statistically significant.

5 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. 293 (a) (b) Fig. 1. Leachable fractions and phs of (a) TCLP and (b) JLT-13 leachates.

6 294 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. Fig. 2. Leaching rate of the heavy metals by diffusion leaching test. Fig. 3. Leachablility index (Ll) of MHW fly ash treated with OPC and with OPC mixed with Ac or Rh.

7 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. 295 Fig. 4. Unconfined compressive strengths of MHW solidified ash after 7, 14 and 28 days of solidification with OPC. 4. Summary Based on results of the study the following are concluded: (1) The addition of activated carbon/rice husk reduces heavy-metal leaching from solidified fly ash. This is effective for the S/S of fly ash using cement. (2) Only Pb is leached from cement-solidified fly ash with additives. (3) Based on results of the diffusion leaching test, Cr leaching at the initial stage (first to third day) is significant. (4) Increasing the percentage of cement is not effective for decreasing metal diffusibility. (5) Effectiveness of additives for decreasing metal diffusibility is not significant in this study. (6) The addition of activated carbon/rice husk decreases unconfined compressive strength. The solidification and stabilization treatment of ash from MHW proved that our method is a good treatment option, but that the treatment is 3 5 times more costly than the direct landfilling of ash. However, the use of cement, particularly OPC, effectively reduces and binds metals within a solidified matrix. Because metals are bound effectively within a solidified waste matrix, the potential of converting a solidified waste matrix to bricks and tiles for pavements, parking lots and bicycle paths and even for road construction was explored. As such, the solidified matrix does not need to be disposed of in landfill sites but instead can be used to manufacture useful products and thus generate income.

8 296 Environmental Sciences, 13, 5 (2006) A. Pariatamby et al. References 1 Department of Environment, Ministry of Science, Technology and the Environment, Malaysia (2002). Malaysia Environmental Quality Report 2001, Machentar Printers Sdn. Bhd. Kuala Lumpur. 2 Batstone, Roger, James E., Smith, Jr., Wilson, D. (1989): The Safe Disposal of Hazardous Waste: The Special Needs and Problems of developing Countries (Volume III), USA : The International Bank for Reconstruction and Development, The World Bank Washington. 3 Leng, T.M. (1996): Hazardous Waste Management in Malaysia Current Status and Issue, paper present in Seminar on Hazardous Waste Management and Disposal: Technology and Strategic Issues. Kuala Lumpur: Institute Kimia Malaysia. 4 USEPA (1992): < 5 Mizutani, S., van der Sloot, H.A. and Sakai, S. (2000): Evaluation of treatment of gas cleaing residues from MSW with Chemical agents, Waste Manage. 20: Cocke and David, L. (1990): The Binding Chemistry and Leaching Mechanisms of Hazardous Substances in Cementious S/S Systems, J. Hazard. Mater. 24: Brown, S.W., Bishop, T., P and Gress, D. (1992): Heavy Metal Binding Mechanism in the S/S Hazardous Waste Treatment Process, pp