Molecular-Scale Understanding of Sulfate Exchange from Schwertmannite by Chromate Versus Arsenate

• DOI: 10.1021/acs.est.0c07980
• Publication Date: 2021-04-09T19:51:21Z
• Authors: Xiaoming Wang; Hong Ying; Wantong Zhao; Xionghan Feng; Wenfeng Tan; Kevin A. Beyer; Qiaoyun Huang; Fan Liu; Mengqiang Zhu
• Keywords: Schwertmannite; Chromate conversion coating

Schwertmannite effectively sorbs chromate (Cr(VI)), yet the sorption mechanisms remain elusive. We determined Cr(VI) on schwertmannite at pH 3.2 and 5 using combined macroscopic experiments with molecular-scale characterization by comparing them to arsenate (As(V)) sorption. adsorbs as bidentate-binuclear (BB) inner-sphere complexes through exchanging more sulfate less >Fe-OH/OH2, 0.59-0.71 released per sorbed. While As(V) also forms BB complexes, it exchanges >Fe-OH/OH2 equally 0.49-0.52 At high loadings, precipitates amorphous FeAsO4, particularly low pH. The abovementioned differences between can be related their different ionic radii binding strength. Moreover, preferentially exchange increasing proportion of outer-sphere in schwertmannite. In turn, concentration increases then decreases loading. Results suggest that an oxyanion, which would form a mineral surface, inner-spherically bound oxyanions than outer-spherically ones even though both are exchanged. This study improves our understanding capabilities template formation stabilize its structure.