School of Environment, Harbin Institute of Technology, Harbin, 150090, China; School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China.
Beijing Huan Ding Environmental Data Research Institute, Beijing, 100083, China.
Chemosphere. 2020 Jun;249:126115. doi: 10.1016/j.chemosphere.2020.126115. Epub 2020 Feb 7.
The BCR sequential extraction scheme (SES), initially developed for soils and sediments, is frequently adopted to evaluate the environmental risks of municipal solid waste incineration (MSWI) fly ash. Within the procedure, metals are liberated from the matrix hosting them relying on the selectivity of the chosen chemical reagents or operation conditions. However, the effect of the high content of alkaline substances in MSWI fly ash on the selectivity of acetic acid to acid-soluble fraction metals was ignored. In this study, the feasibility of the BCR SES for evaluating MSWI fly ash was assessed by adjusting the acetic acid washing times in the acid-soluble extraction step. The metal fractionation, as well as mineralogy, morphology, and surface chemistry of the residues after three successive acid washing processes, were analyzed. The results reveal that only easily soluble salts, but not hydroxides, are entirely extracted after the first acid washing (pH∼12.0). Importantly, carbonates (generally reported as an indicator of the complete release of acid-soluble metals) are mostly decomposed only after the third acid washing (pH∼3.8). The incomplete dissolution of calcium carbonates in a single-step acid washing may convey misleading results of metal fractionation and underestimates the environmental risk of potentially toxic elements. Therefore, complete removal of carbonates should be employed as the endpoint of the acid-soluble fraction extraction step in the evaluation of MSWI fly ash. This work can help in selecting proper strategies for fly ash management and developing proper sequential extraction schemes for similar high-alkalinity hazardous waste risk assessment.
BCR 连续提取方案（SES）最初是为土壤和沉积物开发的，常用于评估城市固体废物焚烧（MSWI）飞灰的环境风险。在该程序中，金属从承载它们的基质中释放出来，这依赖于所选化学试剂或操作条件的选择性。然而，MSWI 飞灰中高含量碱性物质对醋酸对酸可溶部分金属的选择性的影响被忽略了。在这项研究中，通过调整酸溶性提取步骤中醋酸洗涤次数，评估了 BCR SES 用于评估 MSWI 飞灰的可行性。分析了三次连续酸洗涤过程后金属的形态、残留物的矿物学、形态和表面化学。结果表明，只有易溶性盐，而不是氢氧化物，在第一次酸洗涤（pH∼12.0）后完全提取。重要的是，碳酸盐（通常被报告为酸溶性金属完全释放的指标）仅在第三次酸洗涤（pH∼3.8）后才大部分分解。在单次酸洗涤中碳酸钙不完全溶解可能会传达出金属形态错误的结果，并低估潜在有毒元素的环境风险。因此，在评估 MSWI 飞灰时，应将碳酸盐的完全去除作为酸溶性部分提取步骤的终点。这项工作有助于选择合适的飞灰管理策略，并为类似高碱性危险废物风险评估开发合适的连续提取方案。
