The use of calcium carbonate-enriched clay minerals and diammonium phosphate as novel immobilization agents for mercury remediation: Spectral investigations and field applications

• Published in: The Science of the total environment Vol. 646; pp. 1615 - 1623
• Main Authors: Wang, Jianxu, Xing, Ying, Xie, Yuanyan, Meng, Yong, Xia, Jicheng, Feng, Xinbin
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.2019
• Subjects: Clay minerals; In-situ immobilization; Mercury risk management; Spectral investigations; Clay minerals; Spectral investigations; In-situ immobilization; Mercury risk management
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.07.225

We used calcium carbonate-enriched clay minerals (CECM) and diammonium phosphate (DAP) as immobilization agents for mercury (Hg) immobilization. The effects of CECM, DAP, or both in different amounts and ratios, as well as pH and initial Hg concentrations, on Hg removal from solutions were investigated. The removal mechanism was revealed using transmission electron microscope with energy-dispersive X-ray (TEM-EDX) spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The performance of CECM and DAP under field conditions was also studied. The results showed that application of CECM and DAP at a ratio of 50:1 (w/w) removed over 90% of Hg from solutions containing 1.8 μM Hg2+, which was 9- or 2.6-fold higher than solely DAP (<10%) or CECM (34%<), respectively. Mercury removal by CECM and DAP was weakly affected by pH values between 4 and 10, and their maximum Hg removal capacity was 37 mg g−1. Both TEM-EDX and EXAFS results showed that the precipitate of Hg with phosphorus-associated minerals might be the primary mechanism of Hg removal by CECM and DAP. Results from the field trial showed that application of CECM and DAP decreased soil bioavailable Hg contents, but did not affect contents of organic matter bound Hg or residual Hg fractions, as compared with control and initial soils. Application of CECM and DAP resulted in dramatic reductions (40%–53%) of Hg in the edible tissues of Brassica chinensis and Raphanus raphanistrum in comparison to the non-treated control. We conclude that CECM and DAP offer a promising method for in situ remediation of Hg-contaminated farmlands in southwest of China. [Display omitted] •Calcite-enriched minerals and diammonium phosphate were used for Hg immobilization.•Diammonium phosphate reacted with minerals to form phosphate-associated minerals.•Mercury was immobilized with phosphate-associated minerals.•The immobilizing agents decreased Hg bioavailability in the Hg-contaminated soils.•The immobilizing agents inhibited crops Hg uptake.