Phosphate recovery from aqueous solution via struvite crystallization based on electrochemical-decomposition of nature magnesite

Abstract Struvite crystallization was considered to be one of the most promising ways for phosphate recovery. However, the cost of struvite recovery process was too high to be economically attractive. In this work, electrochemical-decomposition of nature magnesite was designed to economically supply magnesium and base for synthesizing struvite, and recover phosphate from aqueous solution. The continuous release of magnesium ions from solid magnesite was achieved by electrochemical action, accompanying by the generation of alkaline solution (pH: 9.0–10.8). The results showed that the electrochemical-decomposition strategy was effective to recover phosphate from aqueous solution as struvite. The key factors of phosphate recovery including current, feed rate, the molar ratio of N/P, initial concentration of phosphate and ammonium, influent pH and plate distance. For a 21-day continuous operation, the recovery rate of phosphate was between 86.6% and 93.3%, confirming the stability of the process. The economic evaluation showed that the proposed electrochemical-decomposition process can reduce the cost of phosphate recovery by up to 60% compare with the traditional chemical process, which using MgSO4·7H2O and NaOH. The struvite with typical orthorhombic crystals was obtained from the bottom of the glass container where the effluent was collected, indicating that part of the ammonium in the solution was also recovered. It was considered that the proposed process may be beneficial to increase the profitability of magnesite mining companies and wastewater treatment plants through selling-buying magnesite material, and subsequent use as a cheaper magnesium source for struvite precipitation.