Treatment of heavy metals contaminated solid wastes-stabilization

Transcription

1 University of Belgrade From the SelectedWorks of Zeljko J Kamberovic 2007 Treatment of heavy metals contaminated solid wastes-stabilization Zeljko J Kamberovic Available at:

2 Treatment of heavy metals contaminated solid wastes-stabilization Treatment of heavy metals contaminated solid wastes-stabilization Mr. Marija Korać, [Željko Kamberović], (Božidar Tomović) Faculty of Technology and Metallurgy, University of Belgrade Karnegijeva 4 Belgrade, Serbia Key words: heavy metals, waste, stabilization, lime, used foundry sand Abstract This paper presents investigation of possibility of heavy metals contaminated solid wastes treatment form Bor Site, Serbia. Presented remediation technology is stabilization, which can effectively reduce content of contaminants in the environment. As a representative of solid waste from investigated site Dam from the Bor copper sulphide ore flotation tailings was chosen. For stabilization of solid waste as stabilizing agenses foundry sand and lime were used. Experiments were conducted by leaching of mixture of solid samples and stabilizing agens or their mixture with sulphuric acid. Change of Cu, Fe, Pb and Zn concentration and change of ph and Eh value were followed during 4 cycles of leaching. Laboratory results of stabilization show that used stabilizing agenses are very effective in stabilization of heavy metals in investigated waste samples. Introduction Solidification/stabilization is one of the most effective methods of dealing with heavy metal contaminated sites. By this method mobility of hazardous substances and contaminates is significantly reduced in the environment through both physical and chemical means [1]. Physical aspect involves changes in mechanical properties of the material and a chemical aspect involves changes to the form and mobility of the contaminants present [2]. The goal of stabilization is to limit migration of hazardous waste into environment by leaching mechanisms [3].Unlike other remedial technologies, solidification and stabilization seeks to immobilize contaminants within their host medium (i.e. the soil, sand etc.) instead of removing them through chemical or physical treatment. For stabilization of contaminated soils, several different stabilizing reagents could be used [4] such as: fly ash, cement or cement kiln dust, lime or lime kiln dust, Proceedings of EMC

3 KoraćKamberović, Tomović phosphates, fluidized bed ash, blast furnace slag cement, silicates and organic polymers. Stabilization is the technology that uses materials as specified to transform contaminated soil containing toxic metals to more manageable forms and/or into less toxic forms by physically and/or chemically immobilizing the contaminants, but also insolubilize, encapsulate, destroy, sorbs etc.[5]. During stabilization soil is incorporated into a monolithic solid with reduced surface area over which leaching occur [6]. The continuing need for development of economical and improved waste management technologies [7], [8] has increased the potential importance of solidification/stabilization technology through out the world, in a process defined as best demonstrated available technology (BDAT) [5], [9], [10]. Used Materials As a representative of heavy metal contaminated soil samples from Dam 3A were chosen. Dam 3A is located on the one end of Veliki Krivelj flotation tailings. Drainage wastewaters from flotation Dam 3A flow into Krivelj River with average flow rate of m 3 /day and than trough Timok River and Danube to Black See [11]. Average chemical composition of these drainage waste water is in mg/l: Cu, Fe and 1.95 Zn [12]. From this site, 25 samples were taken and mean sample was made with chemical composition as presented in Table 1. Table 1. Chemical composition of mean solid sample from dam 3A Element Content, wt.% Method * Cu 0.12 AAS S 1.44 G SiO G Fe 4.06 AAS Al 2 O ICP-AES CaO 2.75 VT MgO 2.21 AAS Pb 0.07 AAS Zn AAS Cu-ox 0.02 AAS As - - * G- Gravimetric analysis, VT-Volumetric titration, ICP-AES-Inductively coupled plasma-atomic emission spectrometry, AAS-Atomic absorption spectrophotometer 692 Proceedings of EMC 2007

4 Treatment of heavy metals contaminated solid wastes-stabilization For stabilization of heavy metals and toxic elements of Dam 3A as a stabilizing agenses lime and used foundry sand were chosen. Advantages of lime and used foundry sand are that they are readily available agenses in this area. Lime originated from Lime factory Zagradja placed within Bor copper mine. Chemical composition of used lime is presented in Table 2. Table 2. Chemical composition of lime from Lime factory Zagradja Element Content, wt. % Method * SiO 2 +unsoluble residue 0.30 G Fe 2 O VT CaO VT Al 2 O ICP-AES MgO 0.52 AAS SO G H 2 O, free 1.33 G H 2 O, crystal G CO G calcinations loss G Used foundry sand (UFS) originated from steel plant US Steel Balkan-Stara Zelezara d.o.o., Serbia [13]. UFS was selected to improve permeability of mixture solid/additive. Second reason for choosing used foundry sand is used binder. UFS originate from ferrous foundries. With addition of binder, water glass, it is used for making moulds by CO 2 process. Water glass is chemically Na 2 O SiO 2 with the different ratio of sodium oxide and silica. All these compounds are transparent, glassy or crystalline solids that have high melting points (above 800 C) and are water soluble and contribute stabilization process. Chemical composition and granulometric analysis of UFS are presented in Table 3. & 4. Table 3. Chemical composition of used foundry sand from US Steel Balkan-Stara Zelezara d.o.o. Element Content, wt.% Method * SiO G Na 2 O 0.54 AAS K 2 O 0.21 AAS CaO 0.32 VT MgO 0.11 AAS Fe 0.92 AAS Table 4. Granulometric analysis of used foundry sand from US Steel Balkan-Stara Zelezara d.o.o. Proceedings of EMC

5 KoraćKamberović, Tomović Particle size, mm Content, wt.% Experimental procedure and results For studying leaching behaviour of metals in the soil/additive system, column tests were conducted. Experimental set up consisted of glass column (ø 40mm and L=300mm), peristatic pump and 5L reservoir. Schematic preview of experimental set up is presented in Fig Glass column, 2. Peristatic pump, 3. Reservoir, 4. Thermometer, 5. Valves Figure 1. Schematic preview of experimental set up From the reservoir, solution was pumped through pipe system into the column, and from the column pumped into the reservoir. On the bottom end of the column, layers of plastic beads and 694 Proceedings of EMC 2007

6 Treatment of heavy metals contaminated solid wastes-stabilization wool were placed for the easier flow of solution to the pump and disabling contamination of leaching solution. The first experiments were conducted without addition of stabilizing agenses in order to determine leaching characteristics of Dam 3A in acidic leaching environment. Leaching was performed with H 2 SO 4 ph 2 to simulate acid rain trough four cycles. In all other experiments different stabilizing substances were added to solid waste in ratio solid/additive=15/1. Ratio of solid/additive was found in literature as most effective on stabilization of heavy metals [6]. The second and third sets were performed with addition of lime and UFS as single additive to study their influence on leachability of heavy metals, as well as on ph values of leach solution trough four cycles. In the last two experiments stabilizing agens was made from mixture of lime and UFS, but the solid to additive ratio was kept 15/1. Ratio of lime and UFS was 1/3 and 1/9, meaning the additive contained 10 and 25% of lime. Change of ph value for all experiments is presented in Figure dam3a lime ufs ufs10lime ufs25lime 8 ph Cycle Figure 2. Change of ph value for leaching Dam 3A without and with different additives with H 2 SO 4, ph=2 As seen in this Figure, when leaching Dam 3A alone or with addition of UFS as single stabilizing agent ph value stayed low, <4. This waste water due to its low ph value couldn t be disposed in natural water streams. Opposite of this when lime was single additive ph value was to high Proceedings of EMC

7 KoraćKamberović, Tomović ~12.5, increasing dissolving of neutralized heavy metals. In the cases when mixture of lime and UFS was used as stabilizing agens, ph values were in optimal range, Chemical analysis of leaching solution after treatment of solid samples with different additives after 4 cycles is presented in Table 5. (discharge limits, domestic and European, of investigated metals is presented in Table 6.). Table 5. Chemical analysis of leaching solution after 4 cycles mg/l mixture metal dam 3A dam 3A +(100%lime) dam 3A +(100%UFS * ) dam 3A + (90%UFS+10%lime) dam 3A + (75%UFS+25%lime) Cu Fe Pb <1 <1 <1 <1 Zn Cu Fe <0.05 <0.05 <0.05 <0.05 Pb <1 <1 <1 <1 Zn 0.34 <0.1 <0.1 <0.1 Cu Fe Pb <1 <1 <1 <1 Zn Cu n.d n.d n.d Fe Pb Zn Cu n.d n.d n.d Fe Pb n.d. n.d. n.d. n.d. Zn Table 5. show that leaching of Dam 3A alone and with single additives (lime and UFS) isn t presenting satisfactory results of heavy metals stabilization. More or less all values of metals concentrations are above discharge limits, domestic one s in the first place. Table 6. Discharge limits for Cu, Fe, Pb an Zn 696 Proceedings of EMC 2007

8 Treatment of heavy metals contaminated solid wastes-stabilization Element, mg/l Domestic European Cu Fe Pb Zn When the mixture of additives is used results are significantly better. For all metals level is below discharge limit, just for lead when ratio of lime and UFS is 1/9. But when ratio is 1/3 concentration of lead in leach solution is below discharge limit. Figure 7. represents Eh, mv evolution with time, measured after each cycle of column experiments wit mixture of used foundry sand and lime as additives ufs10lime ufs25lime Eh, mv Cycle Figure 7. Change of Eh, mv with time for different ratios of UFS and lime in additive mixture Eh of leaching solutions for both ratios of used foundry sand and lime remain at negative values, which indicates that investigated systems have poor oxidative conditions. Conclusion Proceedings of EMC

9 KoraćKamberović, Tomović Additives made from mixture of used foundry sand and lime in different ratios showed to be very effective in stabilization of copper, zinc and iron within dam3a. Concentrations of these metals in leaching solutions are lower than discharge limits, so this kind of wastewater could be safely discharged to natural water streams. Concentration of lead if used 10% of lime in additive is 0.714mg/L, which is higher than discharge limit, but if using 25% of lime in additive lead is not detectable. Stabilization of Dam 3A using dual layer of additives made from mixture of UFS and lime in different ratios showed to be promising remediation technology. References [1] Solidification/Stabilization, Remediation Technologies Screening Matrix and Reference Guide, Version 4.0, [2] Mckinley J.D., Thomas H.R., Williams K.P., Reid J.M. (2001): Chemical analysis of contaminated soil strengthened by the addition of lime, Engineering Geology 60, [3] Trusell S., Batchelor B. (1993): Leaching of heavy metals from solidified wastes, Waste Management, Vol. 13, No. 5-7, [4] Solidification-Stabilization, RECON-Remedial Construction Services, -stabilization.html [5] Malviya R., Chaudhary R. (2006): Factor affecting hazardous waste solidification/stabilization: A review, Journal of Hazardous Materials B137, [6] Yukselen M.A., Alpaslan B. (2001): Leaching of Metals from soil contaminated by mining activities, Journal of Hazardous Materials B87, [7] D. Panias, A. Xenidis, E. Christodoulou, I. Paspaliaris, Metallurgical Solid Wastes: Legislation, Characterization and Management, Wastes From and For the Metallurgy 2001, Varna, Bulgaria, June 2001, pp [8] I. Paspaliaris, K. Komnitsas, S. Durucan, A. Korre, M. Zilberschmidt, V. Nosach, S. Groudev, Environmental Management of Hazardous Mining Wastes and Effluents, Proceedings of the Fourth Annual Eurothen Workshop (Eurothen 2001), Stockholm, Sweden, July 2001, pp [9] Conner J.R. (1990): Chemical Fixation and Solidification of Hazardous Waste, Van Nostrand Reinhold, New York [10] Barth E.et al. (1989): Stabilization and Solidification of Hazardous Wastes, Noyes Data Corporation, New Jersey, USA 698 Proceedings of EMC 2007

10 Treatment of heavy metals contaminated solid wastes-stabilization [11] M. Korać, Ž. Kamberović, Characterization of Wastewater Streams from Bor Site, 4 th Balkan Conference on Metallurgy, Proceedings, Serbia, Zlatibor, September, 27-29, 2006, [12] Integrated treatment of industrial wastes towards prevention of regional water resources contamination, [13] M. Korać, M. Gavrilovski, Ž. Kamberović, I.Ilić, Possibility of used foundry sand exploitation in civil engineering, Acta Metallurgica Slovaca, Special issue, Vol.12, 2006, Proceedings of EMC