Toxicity Reduction And Valuable Metal Recovery For Acid-leaching Residue From Zinc Oxides Dust Using Brine Leaching

It's meaningful to develop a cost-effective and environment-friendly technology for both reuse and toxicity reduction of the smelting slag. In this study, an acid-leaching residue from zinc oxides dust which was collected from an antimony smelter in Guangxi Province of China was investigated. The characteristics and the potential toxicity of the acid-leaching residue were studied. Laboratury-scale tests were conducted in order to optimize the leaching parameters in acidic brine sulotion for the metal recovery from the acid-leaching residue, such as the concentration of HCl and NaCl, pulp density, temperature, reaction time and particle size. The brine leaching residue was washed with water to remove residual chlorine. Pregnant solution from brine leaching was precipitated using Na2S to recovery As and Sb, then In, Zn, and Pb were extracted from the filtrate. The main conclusions are as follows:The valuable metals and toxic elements in the acid-leaching residue mainly are In, Pb, Sb, Zn, As and Cd, with the concentration of 2800,43954,103278,166591,8219 and 1425 mg-kg-1, respectively. However, the acid-leaching residue is slightly corrosive. The fraction of Sb in the acid-leaching residue mainly exists in residual form, while those of As, Cd, Cu, Pb and Zn in the residue mainly exist in acid-extractable, oxidizable and reducible form. The precentage of the overall extractable fractions to the corresponding total As, Cd, Cu, Pb and Zn are 87.5%,95.8%,98.2%,81.1% and 95.3%, respectively. The concentration of As, Cd, Pb and Zn in leachate from the toxicity evaluation experiment is As 24.8, Cd 32.2, Pb 53.6, Zn 6041 mg-L-1, respectively, which far exceeds Standard Identification Values (GB5085.3-2007).The results of NaCl-HCl brine leaching experiments show that the concentration of NaCl and HCl, as well as pulp density have significant effects on the extraction of In, Pb, Sb, Zn, As and Cd from the acid-leaching residue, while the effects of temperature, reaction time and partical size are slight. The optimum conditions for the extraction of In, Pb, Sb, Zn, As and Cd from the residue are CHCl 2.5 mol·L-1, CNaCl 2.0 mol·L-1, temperature 65℃, pulp density 600 g·L-1, stirring speed 300 r·min-1 and particle size-0.25 mm. After 60 min of treatment at these optimum conditions, the In, Pb, Sb, Zn, As and Cd extraction rate from the residue is 96.5%,90.8%,93.2%,92.9%,91.9% and 93.5%, respectively. With the addition of Na2S, amorphous AS2S3 and Sb2S3 concentrate could be obtained from the pregnant brine leaching solution, respectively. After sulfide precipitation, In, Pb and Zn could be recovered by solvent extraction from the filtrate, respectively, and the residual liquor could be recycled within the brine leaching system.The residual chlorine in the brine leached residue is removed by washing with water. After 90 min of treatment,97.8% chlorine is removed when the brine leaching residue was washed at 55℃, pulp density of 300 g-L-1 and stirring speed of 150 r·min-1. The washing solution could be recycled to the brine leaching section with chloride ion concentration of 28.4 g-L-1. The concentration of chlorine in the washed residue is 2012 mg·kg-1, and the residual content of As, Cd, Cu, Pb, Sb and Zn in the residue is lower than the Standard Identification Levels of Toxic Substance (GB5085.6-2007). The pH value and concentration of toxic elements in the washed residue leachate do not exceed the Relevant Standard Limit Values of Hazardous Wastes (GB5085.3-2007). The washed residue becomes the harmless solid.