1. The fate of Cd during the replacement of Cd-bearing calcite by calcium phosphate minerals.
- Author
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Guo, Jianan, Wu, Shijun, Zhang, Xiaohang, Xie, Hong, Chen, Fanrong, Yang, Yongqiang, and Zhu, Runliang
- Subjects
PHOSPHATE minerals ,CALCIUM phosphate ,CALCITE ,CARBONATE minerals ,SODIC soils ,FERTILIZER application ,PHOSPHATE fertilizers - Abstract
Carbonate-bound speciation is a critical sink of potentially toxic elements (PTEs) like cadmium (Cd) in soil and sediment. In a phosphate-rich environment, carbonate minerals could be replaced by phosphate minerals such as dicalcium phosphate dihydrate (DCPD, also known as brushite), octacalcium phosphate (OCP), and hydroxylapatite (HAP). Currently, it is unclear the migration and fate of PTEs during the replacement of PTEs-bearing carbonates by HAP and related intermediate minerals. Therefore, we synthesized Cd-bearing calcite by the coprecipitation method and converted it to DCPD, OCP, and HAP to investigate the redistribution and fate of Cd. The results showed that Cd incorporation in calcite significantly inhibited their replacement by DCPD and OCP, respectively. 1.26% of Cd in calcite was released into the solution when DCPD replaced calcite, and subsequently, most of the released Cd was recaptured by OCP. Significantly, the released Cd was below 0.05‰ when all the solid converted to HAP. These results suggested that with the application of phosphate fertilizer in alkaline soil, the secondary calcium phosphate minerals could control the environmental behavior of Cd. [Display omitted] • Cd in the precursors acts as an inhibitor for calcite-DCPD and DCPD-OCP replacement. • Secondary calcium phosphates inherited over 98% Cd in the precursor minerals. • Calcite-HAP replacement at low temperatures released more Cd than at high temperatures. • One-step replacement of calcite-HAP released more Cd than multi-step replacement. • Cd-bearing DCPD has a higher Cd release risk than calcite and other calcium phosphates. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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