Smelter slag is generally the useless waste residue left after extracting useful metals by hydrometallurgy. Because sulfuric acid and other acidic or alkaline solutions are generally used for leaching, the compounds of harmful metals such as cadmium in the ore change (the original compounds are very stable in the ore) and become unstable compounds or simple metals. When it accumulates in nature, it will seep into soil or flow into rivers to pollute the environment due to corrosion such as rain, which will endanger human health.
Therefore, generally, leaching water residue needs to be treated before it can be discharged or piled up. Recently, many smelters have had such accidents, such as cadmium slag pollution in Guangxi Jinhe Mining Co., Ltd., Xiangjiang pollution in Zhuzhou Smelter and so on.