Institute of Geological Sciences, University of Bern, Switzerland.
Institute of Geological Sciences, University of Bern, Switzerland.
Waste Manag. 2017 Apr;62:147-159. doi: 10.1016/j.wasman.2016.12.004. Epub 2016 Dec 20.
This study focusses on chemical and mineralogical characterization of fly ash and leached filter cake and on the determination of parameters influencing metal mobilization by leaching. Three different leaching processes of fly ash from municipal solid waste incineration (MSWI) plants in Switzerland comprise neutral, acidic and optimized acidic (+ oxidizing agent) fly ash leaching have been investigated. Fly ash is characterized by refractory particles (Al-foil, unburnt carbon, quartz, feldspar) and newly formed high-temperature phases (glass, gehlenite, wollastonite) surrounded by characteristic dust rims. Metals are carried along with the flue gas (Fe-oxides, brass) and are enriched in mineral aggregates (quartz, feldspar, wollastonite, glass) or vaporized and condensed as chlorides or sulphates. Parameters controlling the mobilization of neutral and acidic fly ash leaching are pH and redox conditions, liquid to solid ratio, extraction time and temperature. Almost no depletion for Zn, Pb, Cu and Cd is achieved by performing neutral leaching. Acidic fly ash leaching results in depletion factors of 40% for Zn, 53% for Cd, 8% for Pb and 6% for Cu. The extraction of Pb and Cu are mainly limited due to a cementation process and the formation of a PbCu-alloy-phase and to a minor degree due to secondary precipitation (PbCl). The addition of hydrogen peroxide during acidic fly ash leaching (optimized acidic leaching) prevents this reduction through oxidation of metallic components and thus significantly higher depletion factors for Pb (57%), Cu (30%) and Cd (92%) are achieved. The elevated metal depletion using acidic leaching in combination with hydrogen peroxide justifies the extra effort not only by reduced metal loads to the environment but also by reduced deposition costs.
本研究侧重于粉煤灰和浸出滤饼的化学和矿物学特性，以及确定浸出过程中影响金属迁移的参数。研究了瑞士三座不同的城市固体废物焚烧（MSWI）电厂粉煤灰的浸出工艺，包括中性、酸性和优化的酸性（+氧化剂）粉煤灰浸出。粉煤灰的特征是含有难熔颗粒（铝箔、未燃烧的碳、石英、长石）和新形成的高温相（玻璃、钙长石、硅灰石），周围环绕着特征粉尘环。金属随烟气（氧化铁、黄铜）携带，并富集在矿物聚集体（石英、长石、硅灰石、玻璃）中，或作为氯化物或硫酸盐蒸发和冷凝。控制中性和酸性粉煤灰浸出的金属迁移的参数是 pH 值和氧化还原条件、液固比、提取时间和温度。进行中性浸出几乎不会使 Zn、Pb、Cu 和 Cd 耗尽。酸性粉煤灰浸出导致 Zn 的耗竭因子为 40%，Cd 为 53%，Pb 为 8%，Cu 为 6%。Pb 和 Cu 的提取主要受到固溶体作用和 PbCu 合金相形成的限制，其次是由于二次沉淀（PbCl）。在酸性粉煤灰浸出过程中添加过氧化氢（优化的酸性浸出）通过氧化金属成分来防止这种还原，从而显著提高了 Pb（57%）、Cu（30%）和 Cd（92%）的耗竭因子。酸性浸出与过氧化氢联合使用以提高金属耗竭率不仅可以减少环境中的金属负荷，还可以降低沉积成本，因此值得付出额外的努力。
