Magnesium desulphurization wastewater in copper smelting industry contains high concentration of heavy metal ions such as Cu²⁺ and Mg²⁺. The traditional "neutralization—flocculation" process has problems, such as high treatment costs, waste of heavy metal resources and great risk of environmental pollution. In view of the above problems, the two-step precipitation method of "sulfurization and impurity removal—sodium hydroxide precipitation" was studied to recover copper and magnesium from desulfurization wastewater. Firstly, Cu²⁺ was preferentially precipitated by precise placement of sodium hydrosulfide (1.1 times the theoretical amount) to form CuS. Secondly, sodium hydroxide is used to adjust pH and promote Mg²⁺ to produce magnesium hydroxide efficiently. The effects of pH, NaHS dosage, reaction temperature, reaction time and stirring speed on the recovery of copper and magnesium hydroxide were investigated. The results show that the recoveries of copper and magnesium hydroxide can reach over 95% under the optimal conditions. The process technology is feasible, not only reduces the discharge of heavy metals, but also the CuS formed can be used as raw materials for copper smelting production, and magnesium hydroxide can be reused in desulfurization system. A circular economy model of "pollutant treatment—resource regeneration—process closed loop" is constructed, which can provide technical reference for the recycling of wastewater in metallurgical industry.

desulfurization  /  wastewater  /  copper  /  magnesium  /  recycle  /  heavy metals  /  impurity removal  /  precipitation