Research On The Treatment Of Arsenic-Containing Dilute Acid By Sulphide-Spray Absorption

The arsenic-containing dilute acid is produced from the acid-scrubbing purification section in sulfuric acid plants. At present, the common neutralization method used in our country may produce a mass of arsenic residue, which is difficult to utilize as resources, and long-term stacking is easy to cause secondary pollution. Moreover, the leaching solution can not be recycled but to discharge, leading to serious environmental pollution. On the basis of previous studies and the perspective of resource recovery of residue and reduction of pollution, the technology that industrial barium sulfide ("black ash") was used as raw material to leach barium sulfide, which then reacted with sulphuric acid to produce hydrogen sulfide and by-product precipitated barium sulfate, and the arsenic in solution was removed by spray absorption of hydrogen sulfide was studied in this paper. The effects of the main process parameters on leaching rate and concentration of barium sulfide, purity and whiteness of precipitated barium sulfate, the treatment effect of arsenic-containing dilute acid, and the utilization of sulfur were studied respectively. The research conclusions were obtained as follows:(1) In the process of leaching barium sulfide with"black ash"as raw material, leaching temperature, leaching time, liquid-solid ratio and barium sulfide initial concentration were the main factors which influenced the leaching rate of barium sulfide and the final concentration of barium sulphide solution. In order to obtain a higher leaching rate and concentration of barium sulfide and based on the comprehensive consideration of energy consumption, resource utilization, water consumption, the production efficiency, etc., the optimized technological conditions for leaching barium sulphide was:liquid-solid ratio 4, leaching time 30 min, leaching temperature 90℃, barium sulfide initial concentration 0.217 mol/L. Under these conditions, the leaching rate of barium sulfide was 95.02%, and the concentration of barium sulphide solution was 1.156 mol/L.(2) In the process of by-producing barium sulfate, the purity and whiteness of precipitated barium sulfate were affected by the main factors of feeding sequence, concentration of sulfuric acid and barium sulfide, feeding time, reaction temperature, etc. Under the optimized conditions of barium sulfide concentration 0.79 mol/L, reaction temperature 95℃, feeding time 10.00 min, sulfuric acid concentration 0.8 mol/L, the purity of barium sulfate reached the best value of 97.21%, which achieved the purity requirement of industrial precipitated barium sulfate qualified products of 95%, and the whiteness of barium sulfate was 87.3%, which closed to the whiteness requirement of industrial precipitated barium sulfate qualified products of 88%. The generation of hydrogen sulfide gas in this process could be used for subsequent arsenic removal process.(3) The technology of using spray absorption of hydrogen sulfide to treat the arsenic-containing dilute acid was feasible. Concentration and flow rate of hydrogen sulfide and sulfur-arsenic mole ratio were the main factors which influenced the effect of arsenic removal. In order to recycle using the treated dilute acid and make the arsenic slag meeting the quality requirements of industrial arsenic grade, the optimized conditions in this process was:hydrogen sulfide concentration 1.602 g/L, flow rate 200 L/h, sulfur-arsenic mole ratio 2.40. Under these conditions, the arsenic content in solution after reaction was 0.001756% (17.56 mg/L), and the arsenic removal rate was 99.91%., In addition, excess amount of sulfur was 8.86 g, the sulfur in hydrogen sulfide excess 7.02%, and the sulfur utilization rate of one-stage spray absorption was 92.98%. The treated dilute acid could be supplied to the drying and absorption section for recycling use as supplementary fluid. The arsenic content in arsenic slag after filtration was more than 30%, which could be used as arsenic resources.This treatment technology effectively dealt with the arsenic in dilute acid wastewater, and the by-products of barium sulfate and arsenic slag could be used as resources, which have certain environmental benefits and economic benefits.