Efficient removal of metals and resource recovery from acid mine drainage by modified chemical mineralization coupling sodium sulfide precipitation

Acid mine drainage (AMD) seriously pollutes the environment due to its high acidity and a variety of heavy metals. Although lime neutralization has traditionally been employed to treat AMD, it comes with disadvantages, such as the large quantity of lime required and the generation of substantial amounts of neutralized sludge. Hence, we propose a modified chemical mineralization coupled with sodium sulfide precipitation to simultaneously recover metals from AMD and neutralize acidity. The modified chemical mineralization process effectively removed total iron (TFe) and SO₄^2- through chemically forming schwertmannite (Sch). By regulating temperature and H₂O₂ addition mode, the hydrolysis of Fe³⁺ and SO₄^2- in chemical mineralization was significantly enhanced, resulting in a high yield of Sch. Subsequent introduction of sodium sulfide to already-treated AMD using modified chemical mineralization could harvest or recover other valuable metals other than Fe and maintain a neutral pH of the final effluent. The metal levels in the sulphide precipitation reached as high as 17.9 mg/g, which was three times higher than that achieved through lime neutralization (6.3 mg/g). Moreover, the cost of treating AMD was 15 Chinese Yuan (CNY)/m³ AMD, which was significantly lower than that of lime neutralization (35 CNY/m³ AMD). Therefore, this approach has a good engineering application prospect in actual AMD treatment.