Potential use of magnesium carbonates and hydroxycarbonates as alternative magnesium sources for struvite precipitation

Struvite precipitation economic feasibility is largely controlled by the cost and reactivity of the magnesium source. This research explores the feasibility of three different magnesium (hydro)carbonates as alternative magnesium sources for struvite precipitation: nesquehonite, dypingite and hydromagnesite. These reagents were tested and compared to industrial-standard magnesium sources: magnesium chloride and magnesium hydroxide. Dissolution experiments showed that nesquehonite dissolved significantly faster than dypingite and hydromagnesite, with kinetics closely matching those of MgCl2. In batch precipitation experiments, this higher dissolution rate led to higher magnesium concentrations and faster phosphorus precipitation, clearly outperforming dypingite, hydromagnesite and magnesium hydroxide, while resembling the performance of magnesium chloride. Nesquehonite suitability for struvite precipitation was also confirmed with the continuous operation of a fluidized bed reactor, where high phosphorus recovery (~94%), stable process performance and the production of high-purity struvite were achieved. Overall, these results demonstrate the suitability of nesquehonite to support struvite-based phosphorus recovery, combining rapid dissolution, high phosphorus recovery efficiencies, stable continuous operation, and high-purity struvite.