施氏矿物的化学合成及其对含Cr(Ⅵ)地下水吸附修复

Adsorptive Remediation of Cr(Ⅵ) Contaminated Groundwater with Chemically Synthesized Schwertmannite

采用简单快速的化学合成方法在实验室人工合成施氏矿物,研究了合成的施氏矿物对地下水中Cr(Ⅵ)的吸附动力学、吸附能力以及环境条件对施氏矿物吸附Cr(Ⅵ)的影响.结果表明,合成的施氏矿物对水溶液中Cr(Ⅵ)具有较强的吸附作用,24 h后反应达到平衡,吸附动力学过程符合Lagergren二级速率方程;而吸附等温方程符合Langmiur方程,pH值在4.5~6之间时Cr(Ⅵ)的去除效果最佳,最大吸附能力达到40.4 mg·g-1.溶液中Cr(Ⅵ)的去除率随施氏矿物投加量的增大而升高.Cl-对施氏矿物吸附地下水中Cr(Ⅵ)无明显影响,而HCO_3^-、SO_4^(2-)会对施氏矿物吸附Cr(Ⅵ)产生较为显著的抑制作用;有机物和Ca^(2+)、Mg^(2+)等无机阳离子对施氏矿物吸附Cr(Ⅵ)的影响受pH值的影响:pH=6时,有机物和无机阳离子基本对施氏矿物吸附Cr(Ⅵ)无影响;pH=8时有机物以及无机阳离子均会对施氏矿物吸附Cr(Ⅵ)产生明显的抑制作用.

Schwertmannite is usually naturally found in acidic mining wastewater and frequently used in the adsorption of heavy metal anions from water and wastewater. Schwertmannite was synthesized through a facile chemical method and utilized to remove Cr（Ⅵ） from contaminated groundwater. The kinetics, thermodynamics and isotherms, as well as the effects of environmental factors on the Schwertmannite adsorption processes were investigated. The experimental results showed that the synthesized Schwertmannite had a strong adsorption capability of Cr（Ⅵ） from aqueous solution. At the pre-set initial concentrations of Cr（Ⅵ）, the Schwertmannite adsorption of Cr（Ⅵ） achieved equilibrium within 24 h, and the Lagergren’s second-order model fitted the adsorption process better compared to Lagergren’s first-order model and intraparticle diffusion model. Langmiur equation fitted the adsorption isotherms better than Freundlich equation. The Cr（Ⅵ） adsorption on Schwertmannite mainly involved ion exchange reaction between Cr（Ⅵ） and anions such as OH ^- and SO4^2 - and surface complexation reactions. The △H^θ and △G^θ were 6. 368 kJ·mol ^- 1 and - 1. 215 kJ·mol ^- 1 , respectively, therefore the adsorption of Cr（Ⅵ） was a spontaneous and endothermic process. The removal of Cr（Ⅵ） from aqueous solution increased with increasing Schwertmannite dosage at pH = 4. 5. Acidic pH in the range of 4. 5-6 favored Cr（Ⅵ） removal with Schwertmannite compared to that under basic conditions. Under the conditions of 5 mg·L ^- 1 of initial Cr（Ⅵ） concentration, 0. 5 g·L^ - 1 of Schwertmannite dosage, pH = 6, maximum Cr（Ⅵ） removal of 93. 1% was achieved and the adsorption capacity of Cr（Ⅵ） with Schwertmannite reached up to 40. 4 mg·g ^- 1 . Batch tests showed that the presence of HCO -3 and SO2 -4 inhibited the adsorption of Cr（Ⅵ） while Cl ^- had no significant impact. Cations and natural organic matter had a pH-dependent impact on Cr（Ⅵ） removal： at pH = 8 natural organic matter and cations would significantly inhibit the Cr（Ⅵ） sorption, while the impact could be neglected at weak acidic conditions （pH = 6）.