在工程中使用过量的还原剂,以确保铬铁矿加工残渣(COPR)的可靠修复效果,然而,尽管在固化期后Cr(VI)含量满足法规要求,但修复的COPR在一段时间后发生再黄变现象。该问题是由于使用USEPA方法3060A的Cr(VI)测定的负偏置。为了解决这个问题,本研究试图揭示干扰机制,并提出了两种修正偏差的方法。离子浓度的结果,紫外-可见光谱,XRD,和XPS一起表明Cr(VI)被离子(Fe2+,S52-)在USEPA方法3060A的消化阶段,结果,方法7196A不能反映真实的Cr(VI)浓度。过量还原剂对Cr(VI)测定的干扰主要发生在修复后的COPR固化期,但随着还原剂被空气逐渐氧化,它会随着时间的推移而减少。与热氧化相比,在碱消化之前用K2S2O8进行的化学氧化效果更好地消除了过量还原剂带来的掩蔽效应。这项研究提供了一种如何准确确定修复的COPR中Cr(VI)浓度的方法。这可能有助于减少再黄变现象的发生可能性。
Excessive reductants are used in engineering to ensure a reliable remediation effect of chromite ore processing residue (COPR), however, re-yellowing phenomenon of remediated COPR occurs after some time though the Cr(VI) content meets regulatory requirements after curing period. This problem is due to a negative bias on Cr(VI) determination using USEPA method 3060A. To address this issue, this study tried to reveal the interference mechanisms and proposed two methods to amend the bias. Results of ion concentrations, UV-Vis spectrum, XRD, and XPS together showed that Cr(VI) was reduced by ions (Fe2+, S52-) in the digestion stage of USEPA method 3060A, and as a result, method 7196A would not reflect the true Cr(VI) concentration. The interference on Cr(VI) determination generated by excess reductants mainly occurs during the curing period of remediated COPR, but it decreases over time as reductants being oxidized gradually by the air. Compared with the thermal oxidation, the chemical oxidation with K2S2O8 prior to alkaline digestion performs better to eliminate the masking effect brought by excess reductants. This study provides an approach on how to accurately determine the Cr(VI) concentration in the remediated COPR. It might be helpful to reduce the occurrence possibility of re-yellowing phenomenon.