硫化物对电镀厂铬污染土壤的稳定化效果及其机理研究

Effect and mechanism of stabilization of chromium contaminated soils in electroplating factory by sulfide-based stabilizers

以某电镀厂旧址内的铬(Cr)污染土壤为研究对象,分别添加多硫化钙(CPS)、硫化钠(Na2S)以及焦亚硫酸钠(Na_2S_2O_5)3种硫化物稳定剂,探究3种稳定剂不同投加摩尔比对土壤中Cr的价态变化、浸出毒性和形态分布的影响.结果表明:CPS对Cr(Ⅵ)还原效果最佳,当CPS投加摩尔比为3时,土壤中Cr(Ⅵ)含量从1587.5 mg·kg-1减少至12.43 mg·kg^(-1),还原效率高达99.2%,然而相同条件下Na_2S和Na_2S_2O_5对Cr(Ⅵ)的还原效率仅分别为55.6%和74.5%.CPS对Cr(Ⅵ)和总Cr稳定效率最高,当CPS投加摩尔比为3时,浸出Cr(Ⅵ)和总Cr浓度分别为0.02mg·L^(-1)和0.32 mg·L^(-1),Cr(Ⅵ)和总Cr稳定效率分别为99.8%和99.1%,此时Cr(Ⅵ)浓度满足GB/T 14848-93《地下水水质标准》规定的限值.相同投加摩尔比下Na2S和Na_2S_2O_5对Cr(Ⅵ)稳定效率分别仅为63.0%和98.9%,对总Cr稳定效率分别为66.5%和77.2%;浸出Cr(Ⅵ)和总Cr浓度随着CPS和Na2S投加摩尔比的增加而降低,然而随着Na_2S_2O_5投加摩尔比的增加,浸出Cr(Ⅵ)浓度持续下降,但总Cr浓度不断升高.CPS和Na2S稳定化后土壤中Cr的有机物结合态变化不大(p>0.05)、铁锰氧化物结合态显著增加(p<0.05).硫化物稳定剂稳定化后土壤中Cr的可交换态含量的变化是影响浸出总Cr浓度变化的主要原因.基于3种硫化物稳定剂对土壤中Cr(Ⅵ)还原效率、Cr(Ⅵ)和总Cr稳定效率和Cr的可交换态含量的影响,CPS投加摩尔比为3时,对该电镀厂铬污染土壤的稳定化效果最佳.

This study aims to investigate the effects of valance change, leaching toxicity and fraction distribution for stabilization of Cr （Ⅵ） using sulfide-based stabilizers （calcium polysulfide （CPS）, sodium sulfide （Na2S） and sodium metabisulfite （Na2S2O5））. The results showed the maximum decrease in Cr （Ⅵ） contents from 1587.5 mg·kg^-1 to 12.43 mg·kg^-1 was achieved with an efficiency of 99.2% at CPS molar ratio of 3. In comparison, the reduction efficiencies by Na2S and Na2S2O5 under the same condition were 55.6% and 74.5%, respectively. CPS shows the highest stabilization effect to Cr （Ⅵ） and total Cr. At CPS molar ratio of 3, the stabilization efficiency of 99.8% and 99.1% was reached for 0.02 mg·L^-1 of Cr （Ⅵ） and 0.32 mg·L^-1 of total Cr concentration, respectively. The Cr （Ⅵ） concentration is well below the standard limit （0.05 mg·L^-1） specified in GB/T 14848-93. With the same molar ratio of Na2S and Na2S2O5, stabilization efficiency of Cr （Ⅵ） were 63.0% and 98.9% and that of total Cr were 66.5% and 77.2%, respectively. The concentrations of Cr （Ⅵ） and total Cr decreased with increased dosages of CPS and Na2S, while Cr （Ⅵ） concentration decreased but total Cr continued to increase with increased dosage of Na2S2O5. The fraction change of organic matter was little （p 〉 0.05） but iron and manganese oxides increased significantly （p 〈 0.05） in soil stabilized by CPS or Na2S. The change of exchangeable content of Cr in soil stabilized by sulfide-based stabilizers was the main reason for the change of total Cr concentration. Based on Cr （Ⅵ） reduction efficiency by three types of sulfide-based stabilizers, stabilization efficiency of Cr （Ⅵ） and total Cr and the exchangeable content of Cr, the best stabilizing effect was observed at CPS molar ratio 3 for the soil contaminated by chromium in electroplating factory.