NaCl-CaCl2熔盐热处理危废焚烧飞灰的重金属转化/稳定研究
Transformation and stabilization of heavy metals in hazardous waste incineration fly ash treated by NaCl-CaCl₂molten salt thermal process
-
摘要: 采用NaCl-CaCl2熔盐在相对低温（600-700 ℃）下热处理危废焚烧飞灰，考察了热处理温度、时间、熔盐/飞灰比对热处理产物中重金属分布和浸出的影响；以探究重金属转化/稳定机理。结果表明，飞灰中重金属通过熔盐或飞灰中氯化物（NaCl、KCl等）直接或间接氯化并富集于熔盐相，其余留存于熔渣；熔盐中重金属占比与其本身的挥发性及热处理温度显著相关；飞灰经600 ℃、1 h、1:5热处理后，Cu、Zn、Cr、Cd、Pb在熔盐中占比分别为84.45%、82.28%、75.35%、93.08%、96.39%，减重63%。硫酸硝酸法熔渣中Cu和Pb浸出率最大可分别下降了88.4%和97.3%，浸出液中未检出Zn、Cd和Cr，满足危废填埋场入场标准。醋酸缓冲溶液法熔渣中Cd、Cr、Cu、Pb、Zn的浸出率分别下降了99.8%、90.5%、98.4%、79.6%、99.9%；且可通过进一步添加CaO（4%）调配NaCl-CaCl2熔盐体系，提升熔渣中Pb稳定性。Abstract: Hazardous waste incineration fly ash was thermally treated using NaCl-CaCl₂ molten salt at relatively low temperatures (600–700°C). The effects of treatment temperature, duration, and molten salt/fly ash ratio on the distribution and leaching of heavy metals in the treated products were investigated to explore the transformation/stabilization mechanisms of heavy metals. The results indicate that heavy metals in the fly ash were directly or indirectly chlorinated via the molten salt or chlorides (e.g., NaCl, KCl) present in the fly ash, subsequently enriching in the molten salt phase, while the remaining metals were retained in the slag. The proportion of heavy metals in the molten salt was significantly correlated with their inherent volatility and the treatment temperature. After treatment at 600°C for 1 h with a molten salt/fly ash ratio of 1:5, the proportions of Cu, Zn, Cr, Cd, and Pb in the molten salt reached 84.45%, 82.28%, 75.35%, 93.08%, and 96.39%, respectively, accompanied by a 63% weight reduction. Using the sulfuric acid-nitric acid leaching method, the leaching rates of Cu and Pb in the slag decreased by up to 88.4% and 97.3%, respectively, while Zn, Cd, and Cr were undetected in the leachate, meeting the entry standards for hazardous waste landfills. With the acetic acid buffer solution method, the leaching rates of Cd, Cr, Cu, Pb, and Zn in the slag decreased by 99.8%, 90.5%, 98.4%, 79.6%, and 99.9%, respectively. Furthermore, adding CaO (4%) to adjust the NaCl-CaCl₂ molten salt system enhanced the stability of Pb in the slag.
下载: