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Simultaneous Immobilization of Borate, Arsenate, and Silicate From Geothermal Water Derived From Mining Activity by Co-Precipitation With Hydroxyapatite

Simultaneous Immobilization of Borate, Arsenate, and Silicate From Geothermal Water Derived From Mining Activity by Co-Precipitation With Hydroxyapatite

Keiko Sasaki, Yoshikazu Hayashi, Kenta Toshiyuki, Binglin Guo

Chemosphere. 2018 Sep;207:139-146.

PMID: 29793025

Abstract:

The treatment of the geothermal water discharged through mining activity is a critical issue because the rate of discharge is 12,000 m3 per day and the discharge contains high concentrations of borate (>20 mg/L) and arsenate (ca. 0.4 mg/L) as well as silicate and carbonate. The simultaneous reduction of borate and arsenate concentrations to acceptable levels was successfully performed by co-precipitation with hydroxyapatite (HAp). Although the coexisting high concentrations of carbonate act as a disturbing element, the co-precipitation equilibrium of borate was shifted to lower values by adjusting the P/Ca molar ratio, and the removal rate of borate was accelerated by using Al3+ additives, resulting in the efficient reduction of borate within 1 h. The initially immobilized boron in HAp is in the tetragonal form, which probably occupies the hydroxyl sites in HAp, gradually transforming into the trigonal form in the solid state, as interpreted by 1H NMR and 11B-NMR. The coexisting silicate was also immobilized in an ellestadite form, as confirmed by 29Si-NMR measurements. Arsenate and silicate were immobilized before borate in geothermal water. A dissolution assay of borate in the solid residues after co-precipitation with HAp verified the acceptable stability of borate, which is independent of the amount of added Al3+.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
LS7931396	Trihexadecyl borate			Price

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