Process Route to Generate Double Hydrated Magnesium and Ammonium Sulfates from a Rich Magnesium Sulfate Effluent

Objective: The present study aims to develop a process for treating magnesium sulfate effluents generated from hydrometallurgical processes to produce nickel, copper, or rare earth elements. The primary objective is to propose a process route for generating a hydrated double salt of magnesium and ammonium sulfates by treating an effluent rich in magnesium sulfate. Method: Laboratory-scale experiments using synthetic solutions of magnesium sulfate and ammonium hydroxide, with the addition of sulfuric acid were carried out to promote the precipitation of the double salt under controlled pH and temperature conditions. The product was characterized by nitrogen, magnesium, sulfate, moisture, free acidity, and static hardness. The mineralogy of the product was verified using X-ray diffraction and electron microscopy. Results and Discussion: The double salt presented nitrogen content of 8.3 wt%, magnesium of 8.5 wt%, and sulfate of 58.4 wt%, along with low moisture (1.1 wt%) and free acidity (0.16 wt%). Additionally, the product ((NH4)2SO4.MgSO4.6H2O)) was found to be non-hygroscopic and with suitable particle size (2-4) mm to be applied directly in farms as fertilizer and to obtain NPK blends. Research Implications: It is suggested that the process can be scaled up for industrial applications, providing a value-added product for agriculture and promoting the reuse of industrial waste. Originality/Value: This study is innovative in proposing to treat magnesium sulfate-rich effluents aiming to produce double salt of magnesium and ammonium sulfates with significant potential for agricultural applications.