低分子量有机酸 (苹果酸) 对方解石-氟的吸附/沉淀反应影响.

Low molecular weight organic acids often influence the surface reactions (adsorption/ precipitation) of minerals, which in turn affect the stability of elemental transport in environmental geochemical processes. The effect of malic acid on calcite-fluorine adsorption/ precipitation reactions was investigated. The results show that at the initial pH of 7.7 and lower F concentrations (5 mg·L-1¯), as the concentration of malic acid increases, its surface adsorption capacity becomes stronger and exhibits the inhibitory effects on F removal; at the F concentrations of 25 or 60 mg·L-1, the dominant mechanism of F removal is CaF2 precipitation; the intervention of malic acid shows little inhibition of the CaF, precipitation reaction; the stronger adsorption reaction of malic acid results in an increase of pH and a decrease in Ca concentration. At the initial pH of 8. 3 and low F concentration (<20 mg·L-1), malic acid still inhibits F removal through its competitive adsorption; as the concentration of malic acid increases, its effect of complexation with Cat results in a constant increase in pH and Ca concentration; at the medium F concentration of 60 mg·L-1, the dominant mechanism of F removal has been shifted to CaF2 precipitation; 20 mg·L-1 malic acid has inhibited it, and as the malic acid continues to increase, the pH value decreases and then increases, and the Ca concentration continues to increase, highlighting the effect of the malic acid complexation reaction; At high F concentration of 100 mg·L-1, 100 mg·L-1 malic acid greatly inhibits the CaF2 precipitation reaction, corresponding to a pH value that do not exceed that of the malic acid- free condition; the corresponding Ca concentration is still lower than its blank background value. implying the dominance of the CaF2 precipitation reaction. At the initial pH of 8.7, malic acid has a weak inhibition to F removal at low F concentration (5 mg·L-1); however, as the concentration of malic acid increases, the effect of its complexation reaction becomes much clearer, which results in a significant increase in both pH and Ca concentration; at high F concentration of 240 mg·L-1, the dominant mechanism for F removal is the CaF2 precipitation reaction, which is inhibited with increasing malic acid concentration, with increasing Ca concentration showing the effect of malic acid complexation, and decreasing pH values indicating the dominance of the CaF2 precipitation reaction. This study is important for the stability assessment of calcite minerals in organic acid-rich environments, and also provides a reference for the study of fluorine transport transformation on other minerals. [ABSTRACT FROM AUTHOR]