PENG Li-juan^{1, 2}, WU Shi-jun^1*, GUO Jia-nan^{1, 2}, WANG Mao-lin^{1, 2}, YANG Yong-qiang¹, CHEN Fan-rong¹

(1. CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China)

Abstract: In order to study the migration and conversion regularities of heavy metal elements in the conversion process of heavy metal elements-bearing calcite to apatite, the Cr-calcite samples (containing Cr (III) and Cr (Ⅵ), respectively), synthesized by co-precipitation, were used to study the conversion process of Cr-calcite to apatite under hydrothermal condition. The XRD, FT-IR, SEM, and ICP-OES methods were used to characterize the solid materials and solutions produced in various steps of the conversion process. The results demonstrated that both the Cr(Ⅲ)-calcite and Cr(Ⅵ)-calcite could convert to carbonate-hydroxyapatite in hydrothermal solutions, with over 97% Cr incorporated into the structure of carbonate-hydroxyapatite and only 0.18%－2.06% Cr(Ⅲ) or 0.10%－0.62% Cr(Ⅵ) being released into solutions. The higher temperatures varying from 120 ℃ to 200 ℃, the less of Cr content released into solutions from Cr-calcites during the conversion of Cr-calcite to apatite. Our data showed that most of Cr in Cr-calcite could be immobilized by carbonate-hydroxyapatite via the calcite-apatite conversion, resulting in the reduction of the Cr bioavailability in soil.

Keywords: chromium; calcite; apatite; mineral conversion; migration and immobilization

ACTA MINERALOGICA SINICA Vol. 40, No.3, 2020, page 297-304