Phase evolution and arsenic immobilization of arsenate-bearing amorphous calcium phosphate.

The formation of As(V) substituted hydroxylapatite (HAP) has a vital influence on the fate of As(V) in the environment. However, despite growing evidence showing that HAP crystallizes in vivo and in vitro with amorphous calcium phosphate (ACP) as a precursor, a knowledge gap exists concerning the transformation from arsenate-bearing ACP (AsACP) to arsenate-bearing HAP (AsHAP). Here we synthesized AsACP nano-particles with varied As contents and investigated the arsenic incorporation during their phase evolution. The phase evolution results showed that the transformation process of AsACP to AsHAP could be divided into three Stages. A higher As(V) loading significantly delayed the transformation of AsACP, increased the distortion degree, and decreased the crystallinity of AsHAP. NMR result showed that the PO 4 3- tetrahedral is geometrically preserved when PO 4 3- is substituted by AsO 4 3-. From AsACP to AsHAP, the As-substitution led to the transformation inhibition and As(V) immobilization. [Display omitted] • Phase evolution of arsenate-bearing amorphous calcium phosphate (AsACP) was studied. • As(V) inhibited the formation of arsenate-bearing hydroxylapatite (AsHAP) product. • As(V) immobilization in AsHAP occurs via substitution of PO 4 3- by AsO 4 3-. • The formation of AsACP and AsHAP potentially affects As(V) behavior in vivo / vitro. [ABSTRACT FROM AUTHOR]