不同C/M比HA-Al(Ⅲ)共沉物转化进度对其吸附还原Cr(Ⅵ)的影响机理

The Influence Mechanism of Transformation Extent of HA-Al(Ⅲ)Co-precipitate with Different C/M Ratio on Cr(Ⅵ)Adsorption and Reduction

HA-Al(Ⅲ)共沉物普遍存在于土壤和含水层中,对地下水中的Cr(Ⅵ)具有较强的吸附和还原能力。共沉物中的无定形Al(OH)_(3)不稳定,易转化为三水铝石等晶质矿物,从而对Cr(Ⅵ)的吸附和还原产生影响,但目前对其影响机理尚不明确。本研究分别制备了两种有机碳与金属原子物质的量比值(C/M比)为1和15的HA-Al(Ⅲ)共沉物,并对它们和Al(OH)_(3)单体同步进行了转化处理和表征;利用不同转化进度的HA-Al(Ⅲ)共沉物和Al(OH)3单体开展了Cr(Ⅵ)吸附还原实验,并分析了共沉物转化进度对Cr(Ⅵ)吸附还原的影响机理。实验结果表明,共沉物的转化进度对Cr(Ⅵ)的还原几乎无影响,但对Cr(Ⅵ)的吸附影响显著;随转化进度提高,“类矿物”共沉物(C/M比为1)对Cr(Ⅵ)的吸附量从0.91 mmol·g^(−1)降低至0.21 mmol·g^(−1),而“类有机质”共沉物(C/M比为15)对Cr(Ⅵ)的吸附量几乎未受影响;“类矿物”共沉物对Cr(Ⅵ)的吸附受Al(Ⅲ)矿物表面羟基的络合作用主控,其次为颗粒内扩散作用;随转化进度提高,共沉物及转化产物上表面络合态与颗粒内扩散态Cr(Ⅵ)的量分别随矿物比表面积和孔容的减小而降低;“类有机质”共沉物对Cr(Ⅵ)的吸附和还原主要受HA表面有机官能团的络合和还原作用控制,因此几乎不受矿物晶型转化的影响。

HA-Al(Ⅲ)co-precipitates are widespread in soils and aquifers,and have strong adsorption and reduction capabilities for Cr(Ⅵ)in groundwater.The amorphous Al(OH)_(3) in coprecipitate is unstable and easy to transform into crystalline minerals,such as gibbsite,which will affect the adsorption and reduction of Cr(Ⅵ),but the influence mechanism is still unclear.In this study,two HA-Al(Ⅲ)co-precipitates with atom molar ratios of organic carbon to metal(C/M ratio)of 1 and 15 were prepared,and the transformation and characterization were conducted on both of them synchronously,and taking Al(OH)_(3) monomer as reference substance.The Cr(Ⅵ)adsorption and reduction experiment was conducted using HA-Al(Ⅲ)co-precipitates and Al(OH)_(3) monomer with different transformation extent,and the influence mechanism of transformation extent on Cr(Ⅵ)adsorption and reduction was investigated.According to the results,the transformation extent of the co-precipitate had little effect on Cr(Ⅵ)reduction,but had significant effects on Cr(Ⅵ)adsorption.With transformation extent increasing,the adsorption amount of Cr(Ⅵ)by“mineral-like”co-precipitate(C/M ratio was 1)decreased from 0.91 mmol·g^(−1) to 0.21 mmol·g^(−1),while the adsorption amount of Cr(Ⅵ)by the“organic matter-like”co-precipitate(C/M ratio was 15)was almost unchanged.The adsorption of Cr(Ⅵ)by“mineral-like”co-precipitates was dominated by the complexation of hydroxyl groups on the surface of Al(Ⅲ)minerals,followed by intraparticle diffusion.With transformation extent increasing,the surface complexed and intraparticle diffused Cr(Ⅵ)on the co-precipitates and their transformation products decreased with the decreasing of specific surface area and pore volume respectively.The adsorption and reduction of Cr(Ⅵ)by the“organic matter-like”co-precipitates were governed by the complexation and reduction associated with organic functional groups on HA surface,so it was hardly affected by the mineral transformation in co-precipitates.