Study On Solidification And Strengthening Mechanism Of Arsenic-containing Gypsum Slag Cement

Arsenic bearing gypsum(ABG)sludge derived from lime-ferrous sulfate precipitation process is one of the biggest hazardous wastes in nonferrous metallurgy(Cu,Ni,Pb,Zn,Sn,et al.)industry in China.Nearly one million tons of ABG sludge with different heavy metals'content was stockpiked and leaching toxicity should be well disposed,but it is simply preserved in the reservoir.If it was piled untreated for a long time,it will not only occupy the farmland,but also pollute groundwater,farmland,human's health and ecosystem environment,this kind of sludge treatment needs to be solved.Focusing on this sludge,this study investigated its harmless treatment processes and corresponding mechanisms by the combination of detoxication and stabilization/sodification evaluated in toxic leaching of arsenic.This paper grouped the inadequacy of cement solidification and changed the different additive in S/S,such as glass powder,Potassium permanganate and ferric manganese oxide.It explored the mprovement of the strengthening mechanism of cement solidification.Different factors which influenced the properties of the cementing materials were investigated.With advanced testing methods of XRD,SEM,etc,the solidifying mechanism and the microstructure of products solidified were analyzed.The results showed that ABG sludge mainly consisted of CaS04 and its hydrates accompanied.The toxic leaching of arsenic concentration is 114.06 mg·L-1,(GB)and 125.81 mg·L-1(TCLP),which exceeded the limits of 5mg·L-1 in GB 5085.1-2007(Identification standards for hazardous wastes),respectively.Results show that the traditional cement solidified sludge,arsenic in 28 days later,after sludge addition amount is only less than 30%,toxic leaching of arsenic concentration is less than 5 mg/L.The glass powder and sludge solidification results that glass powder can significantly improve the strength,however,It is bad for the adsorption performance of arsenic ions,so the glass powder can consider as additive in traditional cement solidification,the optimum adding amount was 0.2-5%.Therefore,the arsenic bearing gypsum sludge could be identified as hazardous waste.The removal of free water and crystal water and decomposition of hydroxides,carbonate,arsenite and CaSO4 occurred with the increase of heating temperature,and the toxic leaching of arsenic concentration is less than 5 mg/L in S/S of ABG sludge precalcinated.The results show that iron manganese oxide has the stronger adsorption of arsenic,especially for the As5+ adsorption.Adding 1%cement solidification of iron manganese oxide can decrease the concentration of arsenic leaching toxicity.This scheme not only solves the problem of environmental pollution but also the strengthening mechanism can reduce the mass of cement in the solidification process and it costs low.