硫代硫酸钠、磷酸钠联合处理铬渣中的六价铬

以硫代硫酸钠为还原剂,将铬渣中的六价铬(Cr(VI))解毒转化为三价铬(Cr(III)),并加入磷酸盐作为稳定剂稳定解毒后的铬渣,考察不同反应时间和药剂用量对铬渣中Cr(VI)去除效果的影响.结果表明:硫代硫酸钠可以有效去除铬渣中的Cr(VI),当其与Cr(VI)的摩尔比为理论摩尔比的12倍、处理时间15d时铬渣中Cr(VI)的去除率达到最高(70%),继续增加还原剂用量或延长反应时间均不能有效提高Cr(VI)的去除率.随后加入磷酸钠作为稳定剂,当其物质的量为生成Cr(III)的4倍时,硫代硫酸钠与磷酸钠分步加入(两步法)比同时加入(一步法)处理铬渣的效果较好,处理效果最好时总铬浸出浓度为6.1mg/L,低于危险废物浸出鉴别的总铬标准(15mg/L),而且形成稳定的铬的化合物(CrPO4·6H2O).铬渣pH值变化、五态变化、XRD及XPS分析等结果表明,两步法的处理效果好于一步法.

Remediation of Cr6+ in chromite ore processing residue by sodium thiosulfate and sodium phosphate

Batch experiments were conducted to evaluate the feasibility of the remediation of Cr (VI) in COPR by the reductant sodium thiosulfate (Na2S2O3), and the mechanism for the reduction of Cr (VI) into Cr (III) was tested. After remediation treatment, phosphate was added to immobilize the Cr (III)-containing compounds in COPR. Different reaction time and dosages of reagents were investigated to evaluate the efficiency of Cr (VI) reduction. The results indicated that sodium thiosulfate could effectively remove Cr (VI) from COPR. When the molar ratio of Na2S2O3to Cr (VI) was 12: 1and the treating time was 15 days, 70% of Cr (VI) was removed; afterwards, further increases of reagent dosage and/or treating time had little effect on the removal of Cr (VI). Cr (III)-containing crystallines were observed after phosphate was added as an immobilizer, which significantly reduced the content of Cr (VI) in the COPR leachate. When the molar ratio of phosphate to Cr (III) was 4: 1, the leachable Cr (VI) was 6.1mg/L, which was much lower than the required concentration (￡15mg/L) in China Hazardous Waste Identification Criteria (GB 5085.3-2007). Moreover, the two-step treatment was more beneficial to remove Cr (VI) than the one-step treatment (i.e., Na2S2O3 and phosphate were simultaneously added into the COPR).