Effective treatment of high-arsenic smelting wastewater: Immobilization arsenic and synthesis well-crystallized scorodite

As-containing acidic wastewater from the nonferrous heavy smelting industry is a hazardous As pollution source due to its complex composition, high acidity, and strong toxicity. In this study, an environmentally friendly strategy was proposed to simultaneously remove and immobilize As from acidic wastewater through the synthesis of highly stable scorodite using natural magnetite ore as Fe resource. Firstly, the magnetite ore was dissolved in wastewater to provide a certain amount of starting Fe source for the subsequent arsenic precipitation while creating a suitable pH environment for the synthesis of scorodite. Subsequently, the released Fe ions reacted with As ions in wastewater with undissolved magnetite ore as the nuclear site to form amorphous ferric arsenate, which was then transformed into a well-crystallized scorodite precipitate, thus achieving the As removal and immobilization. Under the optimal reaction conditions, including a Fe/As molar ratio of 2.5, a pre-dissolution time of 5 h, an initial pH of 2.0, a reaction time of 24 h, and a reaction temperature of 90 °C, the residual As concentration in the wastewater rapidly reduced from initial 6259.00 mg/L to 3.76 mg/L, corresponding to an arsenic removal efficiency of 99.94%, and the leaching As concentration in scorodite was 0.42 mg/L. This study provides an efficient and environmentally friendly method for the disposal of high As-containing wastewater from nonferrous smelting.