Preparation of phosphogypsum-based polysulfide and its application in solidified copper-contaminated soil

Heavy metal pollution in soil has been an urgent issue in recent decades. However, traditional stabilization technology is inefficient or costly. In the meantime, the utilization of phosphogypsum is inadequate to cope with a vast annual production in China, resulting in its large-scale stockpiling, which causes environmental pollution and economic detriment. This work provides a new approach for preparing a calcium polysulfide solution to remediate copper-contaminated soil with phosphogypsum as the calcium and sulfur source. Data for this study were collected through simulation calculations, tube furnace experiments, and Cu-contaminated soil treatment experiments. The results showed the optimal decomposition conditions with the best solidification effect, and the highest solidified rate of copper·ions in soil reached 97 %. Phosphogypsum was reduced to CaS and CaO, which synthesize polysulfide by reacting with S. Cu²⁺ was reduced by phosphogypsum-based polysulfide, meanwhile, covalent bonds are formed between Cu and S. This work will generate fresh insight into the resource recycling of phosphogypsum, and solve environmental issues that industry waste and heavy metal pollution in the meantime.