Beijing Key Lab for Source Control Technology of Water Pollution, Beijing Forestry University, Beijing 100083, China; Engineering Research Center for Water Pollution Source Control & Eco-remediation, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Beijing Key Lab for Source Control Technology of Water Pollution, Beijing Forestry University, Beijing 100083, China; Engineering Research Center for Water Pollution Source Control & Eco-remediation, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China.
Sci Total Environ. 2023 Jun 25;879:163192. doi: 10.1016/j.scitotenv.2023.163192. Epub 2023 Mar 31.
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 (Fe, S) 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 KSO 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.
工程中使用过量还原剂来确保铬铁矿加工残渣（COPR）的修复效果可靠，但经过一段时间后，即使修复后的 COPR 中的六价铬（Cr(VI)）含量在养护期后符合法规要求，也会出现再泛黄现象。这一问题是由于 USEPA 方法 3060A 对 Cr(VI)的测定存在负偏差。为了解决这一问题，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、紫外可见光谱、XRD 和 XPS 的结果共同表明，在 USEPA 方法 3060A 的消解阶段，Cr(VI)被离子（Fe、S）还原，因此，方法 7196A 无法反映真实的 Cr(VI)浓度。过量还原剂对 USEPA 方法 3060A 中 Cr(VI)测定的干扰主要发生在修复后的 COPR 养护期，但随着还原剂被空气逐渐氧化，干扰会逐渐减少。与热氧化相比，在碱性消解前用 KSO 进行化学氧化可以更好地消除过量还原剂带来的掩蔽效应。本研究提供了一种准确测定修复后 COPR 中 Cr(VI)浓度的方法，有助于降低再泛黄现象的发生可能性。
