Arsenic effects and behavior during the transformation of struvite to newberyite: Implications for applications of green fertilizers

Abstract

Struvite recovered from wastewaters is an increasingly popular green fertilizer but can sequester hazardous heavy metal(loid)s, including arsenic. The recycled struvite applied as fertilizers in soils often undergoes dissolution and subsequent transformation to newberyite over time, potentially resulting in arsenic contamination. Therefore, understanding the fate of arsenic during struvite transformation to newberyite is critical to its safe application. Herein, we have investigated the effects of arsenic on the transformation of struvite to newberyite and examined the associated consequences of this transformation for arsenic mobilization. Our results demonstrate that low arsenic contents have minor but detectable retardation on the struvite-newberyite transformation, and high arsenic loading can severely inhibit this transformation. However, the mechanisms of the struvite-newberyite transformation are independent of the arsenic concentrations. Most arsenic is retained in the solids during the struvite-newberyite transformation. Also, the arsenic contents in both struvite and newberyite increase with increasing the initial pH values. Moreover, spectroscopic analyses and first-principles calculations show that the dominant arsenic species incorporated is AsO43- in struvite but HAsO42- in newberyite. These results have important implications for understanding the roles of arsenic in struvite-based green fertilizers and developing optimal applications of these materials for the remediation of arsenic contamination in aqueous environments.