Study On The Technology Of Innocuous Treatment Of Silver Leaching Residue Containing Heavy Metal

Silver leaching residue containing heavy metal, which produced by hydrometallurgical extraction of silver, is a kind of hazardous waste, due to its leaching toxicity exceed standard limit. At present, silver leaching residue is reserved as the national standards, instead of discharging into the outside world. However, there are many environmental pollution risks in the long-term stockpiling of the residue, which would be harmful to human health and the ecological environment. In order to remove the unstable heavy metal in silver leaching residue and turn the residue into a stable general solid waste, safety disposal would be taken to eliminate environmental pollution risks. Chloride leaching-ammonium sulfide leaching-water leaching was adopted to selective separate soluble heavy metal from silver leaching residue, making the residue into general solid waste. The processes of chloride leaching of lead, ammonium sulfide leaching of sulfur and arsenic, the thermal decomposition of ammonium polysulfide and water leaching of arsenic were studied in the paper, and the main results are as follows:(1) Multistage pickling cannot effectively remove soluble heavy metals from silver leaching residue, which is difficult to turn the residue into a stable general solid waste. It needs to use other methods to innocent treatment of silver leaching residue.(2) In the process of leaching of lead with chloride, the total chlorine concentration and liquid-solid ratio is the main factor affecting the leaching rate of lead. The optimum conditions were as follows:the stirring speed 600 r-min-1, the concentration of NaCl 2 mol·L-1, the total concentration of chlorine 5 mol·L-1, the ratio of liquid-solid 3, the reaction temperature 80℃, the reaction time 20 min, the concentration of sodium hydroxide 0.01 mol·L-1. Under the optimum conditions, the leaching rate of lead can be up to 94%, and the leaching toxicity of lead is decreased from 194 mg·L-1 to 0.35 mg·L-1, which is below the standard limit (5 mg·L-1).(3) The concentration of ammonium sulfide and the liquid-solid ratio are the main factors of the process, in which sulfur and arsenic removed with ammonium sulfide. The optimum conditions were as follows:the reaction time 20 min, the concentration of ammonium sulfide 2 mol·L-1, the reaction temperature normal atmospheric temperature, the ratio of liquid-solid 2. Under the optimum conditions, the leaching rate of sulfur can be up to 97%. Whereas the dissolution rate of arsenic is about 40%. The optimum conditions of recycling of sulfur by thermal decomposition were as follows:the reaction temperature 90℃, the reaction time 100 min. Under the optimum conditions, the exhalation rate of sulfur can be up to 94%.(4) After the chlorine leaching and ammonium sulfide leaching, using washing method to remove the arsenic from silver leaching residue, its optimum conditions were as follows:the reaction temperature normal atmospheric temperature, the ratio of liquid-solid 8, the reaction time 20 min, pH=7. Under the optimum conditions, the leaching toxicity of the residue is below the standard limit.(5) After the above three innocuous treatments, the leaching toxicity of silver leaching residue is below the standard limit, becoming a general solid waste. The resource utilization of some elements such as sulfur and iron included in the residue, and the lead chloride and sulfur precipitated from the residue, which could finally realize the harmless disposal and resource and minimization of the hazardous waste.