Coprecipitation of Arsenate with Metal O

Arsenic mobilization in soils is predominantly governed by sorption/desorption mechanisms, but it may also coprecipitate with aluminum and/or iron in natural settings. The objective of this study was to investigate the mineralogy, chemical composition, and surface properties of aluminum-arsenate coprecipitates and analyze their behavior in terms of phosphate sorption and arsenate loss. Using a controlled synthesis at varying pH levels (4.0, 7.0, or 10.0) and As/Al molar ratios (0, 0.01, or 0.1), the coprecipitates were aged for different durations and analyzed. Our results indicated that while gibbsite and bayerite formed in the absence of arsenate, poorly crystalline precipitates emerged in its presence. Notably, short-range ordered materials were observed regardless of the pH level. Chemical dissolution tests revealed that arsenate primarily resided in these short-range ordered precipitates, with phosphate sorption being heavily influenced by the specific nature and composition of the coprecipitates. The study highlighted that the desorption of arsenate by phosphate was relatively low, suggesting that arsenate was either occluded or adsorbed. Overall, the findings emphasize the importance of initial conditions and aging on the stability and reactivity of aluminum-arsenate coprecipitates.