Study On Decomposition Characteristics Of Arsenic - Containing Gypsum Slag By Carbon

A large amount of arsenic bearing gypsum sludge was produced in the process of copper refining. And, the copper smelting enterprises were restrained by the technology limitation, environmental regulations and the processing cost, so these sludge still cannot be effectively disposed or used and had to be amassed in the "three-proofing" pool. The "three-proofing" pools not only increased the long-term operation and maintenance costs but also were security risks. And the native ecosystem would be destroyed seriously, when some significant geological disasters such as earthquake, mud-rock flows, and flash floods had occurred. So, the researches and explorations on the innocuity treatment and resource utilization of the gypsum sludge were some big issues to be dealt with and of great significance.This paper grouped the possible chemical reactions in the reductive decomposition process of arsenic bearing gypsum with coal powder and the HSC Chemistry was used to calculate and analysis the ΔrGm(?)e and ΔrHm(?) of every possible reaction. On the basis of chemical composition, phase, leaching toxicity and thermal stability of arsenic bearing gypsum sludge obtained in lime/ferrous sulfate precipitation process, the mass loss of gypsum and the leaching concentration and total content of arsenic in the decomposition residue were investigated by TG-DTG-DSC-FTIR analysis and the fixed bed reactions experiments. Then, the volatilizing rates of arsenic were calculated and this paper essentially determined the reductive decomposition characteristics and arsenic migration rule.The results showed that arsenic bearing gypsum sludge mainly consisted of CaSO4 and its hydrates accompanied with As, Zn, Cu, Sb, Bi, Pb, Cd, Hg, Se and other heavy metal elements. For this sludge, the leaching toxicity of As was 214.06mg-L-1 and the toxicity of Se was 2.47mg-L-1, which exceeded the limits of 5mg-L-1 and lmg-L-1 in GB 5085.1-2007 (Identification standards for hazardous wastes), respectively. Besides, the leaching toxicity of Hg was a little higher than that of limit in GB 5085.1-2007. 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; When the mole ratio of C/S(C/CaSO4) was 1.5, the maximum weight loss rate and the minimum leaching concentration of arsenic,0.14mg/L, can be achieved which was far below the regulation level of China; Adding coal to the gypsum would be conductive to the volatilization of arsenic and the the maximum volatilizing rate reached 98.70%, which was the main cause of the reducing leaching toxicity of arsenic; The phase of CaO could be found in the decomposition residue of gypsum without the adding of coal, while it couldn’t be found in the residue when combined with a certain amount of coal and what could be found was mainly the phase of CaS. Meanwhile, by the XRD analysis it indicated that the smoke dust was mainly consisited of As2O3, which was in accordance with the high volatilizing rate of arsenic; Reductive decomposition of arsenic bearing gypsum sludge realized the harmless disposal and arsenic enrichment.