The Feasibility Of Reduced Liner For Controlling Heavy Metals Pollution

Acid mine drainage (AMD) generated from the natural oxidation of mine wastes and rocks enriched in metals sulfide minerals. This waste water is characterized by a low pH and elevated concentration of heavy metals and sulfates, all of which have a detrimental effect on the ecosystems of mining districts. AMD from mine waste is a serious environmental problem associated with mining industry around the world.Strategies for mitigating the contamination resulted from AMD include source control and treatment of the contaminate water through chemical or biological methods. Prevention of the formation of AMD is generally a favorable option. Past prevention efforts generally include covering the mine wastes, co-disposal with alkaline material, inhibiting the growth of bacterial by spraying batericides, and so on. Segregating the most hazardous material and then disposal of them in a lined contained facility is an innovative technique to preclude the formation of AMD. Liner systems that have been widely used to contain mine waste include compacted clay liner (CCL), geosynthetic clay liner (GCL) and geomembrane (GM), and so on.Reduced liner (RL) is proposed by Lanzhou University, China as a new type containment system for mine wastes. It does not only have a low hydraulic conductivity as traditional hydraulic barrier but also posses strong reducing environment, where favor the formation of precipitation of metal sulfide. The objective of this study is to investigate the potential of municipal sewage sludge as construct material for RL and to assess the long-term integrity of the RL serving at mine waste dump site.Batch sorption test and anaerobic microbial incubation test were conducted to investigate the retardation mechanisms of heavy metals maybe occurred in sewage sludge suspensions. The results of batch sorption indicated that sewage sludge possessed strong adsorption capability for Zn2+ and Cd2+, which of 13.62 mg·g-1 and 15.60 mg·g-1, respectively. Anaerobic microbial incubation test results showed that microorganisms occurring in sewage suspensions can induce the redox condition of sewage sludge suspensions changed from oxidized state to strong reduced state and then promote the formation of sulfide mineral. The strong reducing condition established in sewage sludge suspension promoted the concentrations of heavy metals decrease to a lower level.The hydraulic conductivity of compacted sewage sludge was determined using flexible-wall permeameters. The measured hydraulic conductivity of compacted sewage sludge was lower than the regulatory specifications of 1.0×10-7cm/s for landfill site. Microorganism activity occurred in sewage sludge has the ability to decrease the hydraulic conductivity of compacted sewage sludge.The compatibility of the compacted sewage sludge with acidic pore water spiked with heavy metals was assessed through hydraulic conductivity test. Test results indicated that the permeation of acidic pore water tend to increase the hydraulic conductivity of compacted sewage sludge.The results of this study suggest that sewage sludge is a suitable material for constructing RL. Compacted sewage sludge can provide overall anaerobic reduction condition which decrease the mobility of heavy metals, displaying a potential application in pollution control engineering. With respected to the increase in hydraulic conductivity due to acidic pore water, further research clearified that the addition of alkaline material is needed to enhance the acid compatibility of compacted sewage sludge if used to control AMD.