PRB去除模拟地下水中六价铬的反应特性

Reactivity Characteristics of Hexavalent Chromium Removed by PRB in Simulated Ground Water

采用粒径为0.15～0.42mm的零价铁(Fe0)和粒径为0.15mm的活性炭(AC)作为PRB反应介质,通过连续流动试验研究Fe0/AC-PRB修复模拟污染地下水时反应介质与六价铬〔Cr(Ⅵ)〕的反应特性,分析了AC对Cr(Ⅵ)的去除作用、Fe0对Cr(Ⅵ)的还原作用及其氧化还原产物、Fe0AC对Cr(Ⅵ)的协同去除效果,研究了土壤中残留铬的形态。结果表明,在进水pH为6.9～7.1条件下,AC对Cr(Ⅵ)有一定的去除作用,主要通过吸附对Cr(Ⅵ)加以去除。Fe0对Cr(Ⅵ)有较高的去除率,进水Cr(Ⅵ)浓度为10mg/L时,去除率达96%,氧化还原产物Fe3+和Cr3+与OH-形成沉淀附着在反应介质中,不会迁移到"下游"水体。Fe0/AC电池腐蚀反应可以提高Fe0的还原能力和还原效率,相对于Fe0单独作用时,铬铁比提高了1倍以上,出水pH从原水的7.0上升到8.0左右,铁浓度小于0.20mg/L。经过去离子水冲洗,容易迁移且易于被生物利用的弱酸可提取态铬解吸到水相中,有机物与硫化物结合态和残渣态是含水层土壤中铬的主要存在形态,从生物可利用角度来说,铬的环境风险大大降低。

The zero-valent iron （Fe°） with particle size of 0. 15-0.42 mm and the activated carbon （AC） with redox products of chromium deoxidized, and collaborative continuous flow simulation experiments, the Cr（VI） ） contaminated ground water by Fe°/ e reducing action of Cr（ WI ） by Fe° and their removal effect of Fe°/AC were analyzed, and the speciation of chromium remained in aquifer was investigated. The results showed that Cr（ Ⅵ ） was removed to some extend mainly by adsorption under the conditions of influent pH 6.9-7. 1. Meanwhile, the chromium could be deoxidized by Fe° more effectively, with the efficiency up to 96% while continuously inputting simulated groundwater containing 10 mg/L hexavalent chromium. During the process, the redox products, Fe3＋ and Cr3＋ were precipitated on the reaction medium; therefore they did not transfer into downstream water. Micro-electrolysis improved the reduction capacity and efficiency of Fe°, and compared with the effect of sole Fe°, the ratio of chromium to iron increased by more than 1 time, the pH increased from 7.0 of influent to 8.0 of effluent, and the total iron concentration of effluent was below 0.20 mg/L. Chromium was easily transported and extracted by bioavailable weak acid when the aquifer was flushed with deionized water. Chromium was distributed mainly inorganic/sulphide fractions and residue fraction, which indicated that a low ecological risk of chromium remained in aquifer to environment.