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Coprecipitation with calcium carbonate (CaCO 3 ) could decrease the bioavailability of arsenic (As). However, in a phosphate-rich environment, some CaCO 3 will be converted to hydroxylapatite (HAP). Currently, the behavior of carbonate-bound As during conversion is unclear. Therefore, we prepared bio-induced CaCO 3 in an As solution and converted it to HAP. The results showed that a high concentration of arsenate promoted vaterite precipitation and the conversion of CaCO 3 to HAP. The dissolution data verified the low solubility of As in HAP, though its As-bearing CaCO 3 precursor released up to 88.19% As during the conversion. Furthermore, HPLC-ICP-MS data showed partial oxidation of arsenite to arsenate, suggesting that CaCO 3 and HAP's structure favored the incorporation of arsenate. Our results demonstrated that the stability of heavy metal-bearing CaCO 3 should be considered, and the role of HAP in the immobilization of heavy metals such as As should not be overestimated., (Copyright © 2021 Elsevier B.V. All rights reserved.)

α-Ba2[UO2(PO4)2] (I) and β-Ba2[UO2(PO4)2] (II) are prepared by H3BO3/B2O3 flux reactions using stoichiometric amounts of BaCO3, BPO4, and UO2(NO3)2 (Pt crucible, 1. [ABSTRACT FROM AUTHOR]

K[AsW2O9], prepared by high-temperature solid-state reaction, is the first member of the arsenate–tungsten bronze family. The structure of K[AsW2O9] is based on a 3-dimensional (3D) oxotungstate–arsenate framework with the non-centrosymmetric P212121 space group, a=4.9747(3)Å, b=9.1780(8) Å, c=16.681(2) Å. The material was characterized using X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Raman and infrared (IR) spectroscopic techniques. The results of DSC demonstrate that this phase is stable up to 1076K. Second harmonic generation (SHG) measurements performed on a powder sample demonstrate noticeable (0.1 of LiIO3) non-linear optical (NLO) activity. [ABSTRACT FROM AUTHOR]

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]