Synthesis of lead sulfide by heavy metal gypsum matched with lead paste

The heavy metal gypsum is a hazardous solid waste, which is from the process of lead and zinc metallurgical industry. In this method, heavy metal gypsum and lead paste were used to synthesize PbS by pyrogenic attack. First synthesize CaS by the reducing of heavy metal gypsum that the pulverized coal was used as a reduction agent. Then the production CaS reacted with lead paste to synthesize PbS and the product CaO. The production PbS can be reused as raw materials for the process of lead metallurgical industry and CaO can be used to replace some slag forming constituents or smelting flux. The two-steps method reaction temperatures were 1173 K and 1073 K respectively in a protective atmosphere of nitrogen, wherein the second step was the rate-controlling step. In the final product, the percentage of lead was 70.89%, which exceeded the standard level of lead of industry standard for the nonferrous industry of China. At last, lead element was almost removed from waste gypsum as PbS, with some lead free about 4.5% which can be recycled in the dust catcher system. In this way, heavy metal gypsum can be recycled environmentally, economically and sustainably.