基于硫化钠的垃圾焚烧飞灰EDTA提取液中重金属回收试验研究

Experimental study on recovery of heavy metals from EDTA extraction solution of fly ash from waste incineration based on sodium sulfide

为实现对垃圾焚烧飞灰EDTA提取液中重金属的回收,以硫化钠溶液为沉淀剂,探究了其用量对重金属回收率的影响,并评价了回收后重金属对环境的影响。理论计算结果表明,在pH为9~12的体系中,S^(2-)能与提取液中的重金属离子形成CdS、CuS、PbS、ZnS金属硫化物沉淀。回收试验结果表明,每处理1 L提取液,5%Na_(2)S的适宜用量为40 mL,Na_(2)S用量对各重金属元素的回收率总体上影响不大;提取液处理前,Cd、Cu、Zn和Cr的质量浓度较低,Cd、Pb质量浓度超标,尤其是Pb超出了标准限值的20倍;回收处理后,提取液中Cd、Cr、Cu、Pb、Zn的质量浓度均符合GB 8978-1996的规定;浓度较高的Pb回收效果最为显著,其回收率达95.31%,浓度较低的Cd、Cu、Zn和Cr的回收率分别为63.16%、62.71%、66.37%和54.88%;Cr^(3+)虽然不与S^(2-)反应,但通过包藏、吸附等方式被其他重金属硫化物共沉淀进入重金属回收渣,从而实现分离回收;重金属回收渣中铅质量分数高达4.24%,超过了原生铅矿Pb最低工业品位的4倍多,可以作为一种炼铅资源。本工艺简单、实用性强,为垃圾焚烧飞灰综合利用提供了一条新途径。

To achieve the recovery of heavy metals from EDTA extraction solution of fly ash from waste incineration,sodium sulfide solution was used as the precipitant to investigate the effect of its dosage on the recovery rate of heavy metals,and the impact of heavy metals on the environment after recovery was evaluated.Theoretical calculation results indicate that in the system with pH=9~12,S^(2-)can form CdS,CuS,PbS,and ZnS metal sulfide precipitates with heavy metal ions in the extraction solution.The results of the recovery test showed that the suitable dosage of 5%Na_(2)S was 40 mL per 1 L of extracted solution treated,and the dosage of Na_(2)S had little effect on the overall reco-very rate of each element.Before the treatment of the extracted solution,the mass concentrations of Cd,Cu,Zn,and Cr were relatively low,and the mass concentrations of Cd and Pb exceeded the standard limit,especially Pb exceeding 20 times the standard limit.After recycling,the mass concentrations of Cd,Cr,Cu,Pb,and Zn in the extraction solution all comply with the provisions of GB 8978-1996.The recovery effect of Pb with higher concentration was most significant,with the recovery rate of 95.31%.The recovery rates of Cd,Cu,Zn,and Cr with lower concentration were 63.16%,62.71%,66.37%,and 54.88%,respectively.Although Cr^(3+)does not react with S^(2-),it is co precipitated by other heavy metal sulfides into the heavy metal recovery slag through encapsulation,adsorption,and other methods,thereby achieving separation and recovery.The lead content in heavy metal recovery slag was as high as 4.24%,which is more than four times of the minimum production grade of primary lead ore,and can be used as a lead refining resource.This process is simple and practical,providing a new approach for the comprehensive utilization of fly ash from waste incineration.