采用巯基捕收剂稳定化处理垃圾焚烧飞灰中的重金属

Stabilization of Heavy Metals in Municipal Solid Waste Incineration Fly Ash with the Thiol Collectors

研究了3种巯基捕收剂,二乙基二硫代氨基甲酸钠(乙硫氮)、乙基黄原酸钾(乙基黄药)和二丁基二硫代磷酰铵(丁铵黑药),对垃圾焚烧飞灰中重金属的稳定化效果.3种巯基捕收剂的用量均为62.5μmol.g-1飞灰.扫描电镜观察发现,飞灰经稳定化处理后,巯基捕收剂均匀地覆盖于飞灰晶体表面,使矿物晶体棱角变得模糊.利用酸浸提程序(TCLP法)和水浸提程序(水平振荡法)评价飞灰中重金属Cu、Pb、Cd、Cr和Zn的浸出毒性.在0.1 mol.L-1醋酸浸提条件下,与Na2S相比,巯基捕收剂对Cu和Pb的稳定化效果较好,其中乙硫氮对Cu的稳定化比率接近100%,丁铵黑药对Pb的稳定化比率达到69.2%;在水浸提条件下,乙硫氮、乙基黄药和丁铵黑药对5种重金属的稳定化比率分别为72.6%、73.5%和76.8%,显著高于Na2S处理(52.4%).3种巯基捕收剂对5种重金属亲和力的强弱顺序大致为Cu>Pb>Cr>Cd>Zn,并且超过60%的巯基捕收剂与酸可浸提重金属离子发生了螯合沉淀反应.重金属-巯基捕收剂絮凝物在中性和碱性条件下(pH>6)比较稳定,在酸性条件下(pH<6)可发生部分溶解.为获得较好的重金属稳定化效果,维持稳定化飞灰的高酸缓冲容量十分重要.

Three kinds of thiol collector, sodium diethyldithioearbamate （DDTC）, potassium ethyl xanthate （EXT） and ammonium dibutyl dithiphosphate （DDTP）, were adopted to stabilize heavy metals from municipal solid waste incineration fly ash （MSWI fly ash）. The concentration of the three thiol collectors was all 62.5 μmol· g^- 1 fly ash. Scanning electron microscopic observation shows that, the thiol collectors evenly cover on the surface of fly ash which makes the angles of mineral crystal ambiguous. Furthermore, the leaching characteristics of heavy metal Cu, Pb, Cd, Cr and Zn in fly ash were analyzed according to the toxicity characteristic leaching procedure （TCLP） and the horizontal vibration method. Comparing with Na2S, thiol collectors present better stabilization effects for Cu and Pb when the extraetant is 0.1 mol·L^-1 acetic acid. DDTC stabilizes almost all the acid-extractable Cu, and DDTP stabilizes 69.2% of acid-extractable Pb. When extracted by water, the stabilization ratios of the five heavy metals by DDTC, EXT and DDTP are 72.6%, 73.5% and 76.8%, respectively, significantly higher than that by Na2 S （52.4 % ）. The affinity preference of the thiol collectors for the five heavy metals is generally in the order of Cu 〉 Pb 〉 Cr 〉 Cd 〉 Zn. Also, over 60% of the collector participates in the chelating reaction with the acid-extractable heavy metals. Under neutral and alkali condition （pH 〉 6） the chelators of heavy metal-thiol collector are steady, but partly dissolved under acid condition （pH 〈 6）. Evidently, in order to obtain better heavy metal stabilization effects, it is important to maintain the acid buffer capacity of stabilized fly ash at a higher level.