医疗垃圾焚烧飞灰的分步浮选法去毒及表面活性剂对其增效作用

Hospital solid waste incinerator (HSWI) fly ash was usually classified as hazardous waste because of its high concentrations of toxic heavy metals and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Based on high content of PCDD/Fs and carbon constituents including activated carbon powder and unburned carbon in HSWI fly ash, lipophilic and hydrophobic nature of PCDD/Fs and characteristic of PCDD/Fs enrichment in carbon constituents, a new two-step flotation way of HSWI fly ash is developed on the base of former research of decarburization from fly ash. At the first flotation step, PCDD/Fs and carbon constituents will be enriched and separated from HSWI fly ash, at the same time chloride and heavy metal will be washed out. Two products of carbon-rich froth and slurry remaining will be obtained after flotation. Then, the slurry remaining will be subjected to the second flotation step, where heavy metals such as Pb and Zn in slurry will be removed and recovered. The volume and toxicity of the residual ash will be decreased greatly through two-step flotation process, therefore, the residual ash could be landfill disposed or reused directly. The first objective of this study was to investigate the relation between the removal of PCDD/Fs and decarburization in flotation process and the synergism effect of added surfactant on the removal of PCDD/Fs. The second objective is to elucidate the effect of high content of chloride on critical micelle concentration (CMC) of surfactant and two-step flotation process. The third objective is to investigate the acid leaching pretreatment of heavy metals and mechanisms of the sulfide precipitate flotation. Thus, the goal of furthest separation of toxic matter such as PCDD/Fs, heavy metal and harmless treatment and reuse of HSWI fly ash with low cost will be achieved by flotation. These results will provide useful scientific information and theory of reference for the treatment of HSWI fly ash.

医疗垃圾焚烧飞灰含有相当量的二恶英和重金属等毒害物，属于危险废弃物。申请者针对医疗垃圾焚烧飞灰中二恶英及碳组份（活性炭和未燃残碳）含量高、二恶英在碳组份中富集及二恶英"亲油疏水"的特性，在前期飞灰浮选脱碳研究的基础上，提出医疗垃圾焚烧飞灰两步浮选去毒新思路：一步浮选实现飞灰中的二恶英和碳组份的共分离，同时洗脱氯和重金属，浮选后得到富集碳和尾浆两种产物，二步浮选脱除并回收尾浆中Pb、Zn等重金属。浮选后残灰的体积和毒性将大幅度降低，可考虑直接填埋处置或再利用。本课题着重研究浮选过程中二恶英移除与飞灰脱碳之间关系、表面活性剂对二恶英移除的增效作用、高含量氯盐对表面活性剂的临界胶束浓度（CMC）及两步浮选效果的影响、重金属酸浸－硫化沉淀浮选机制等，力求最大限度地分离飞灰中二恶英和重金属等毒害物，低成本实现飞灰的无害化处理及资源化利用。课题成果将为医疗垃圾焚烧飞灰的浮选去毒提供科学基础和理论参考。

医疗垃圾焚烧飞灰富含重金属、二恶英及碳组分。基于以上飞灰特性，本项目研究工作采用两步浮选法分别移除飞灰中二恶英和重金属。该研究工作所取得的成果如下：发现粒径介于25μm~75μm之间的飞灰质量占82%，非常适合浮选处理；飞灰中二恶英同系物含量均随飞灰粒径的减小而增加，精灰产物中二恶英集中在＜38μm的细粒中；证实不同类型表面活性剂对风化飞灰中碳和二恶英移除的增效作用依次为：非离子Tween80>阳离子CTAB>阴离子SDS，它们对应的最佳浆液pH值分别为7、5和9；当加入5％（w/w）Tween80时，90.6％碳组分和88.6％二恶英可从飞灰中移除；尾灰中残留的二恶英符合填埋场的规定, SDS对重金属的移除率高于Tween80和CTAB；飞灰中存在的高含量氯盐对碳和二恶英移除有促进作用；若同步浮选移除新鲜飞灰中的二恶英和重金属，灰浆的pH值应控制在5左右；若采用分步浮选（脱碳浮选结合离子浮选）回收重金属，离子浮选的参数：SDS浓度、MIBC浓度、叶轮转速和浮选时间的最佳值应分别为480ppm、150ppm、2000rpm、18min，此时，浸出液中Zn、Pb、Cu和Cd的回收率分别达到47.0％，56.5％，57.5％和49.1％；采用再燃方法处理精灰，当再燃温度高于1000℃时，精灰中二恶英的去除率超过98%，Pb、Zn和Cu等重金属的挥发率随再燃温度的升高而增大；采用微波法处理精灰，当微波入射功率为2100W，处理时间为7min时，精灰中二恶英的去除率达到99.6%，且二恶英的总毒性当量从29.0 ng–I-TEQ/g大幅度减少到0.08 ng–I-TEQ/g以下。结果表明：第一步浮选可实现飞灰中二恶英和碳组分的共分离，同时洗脱氯和重金属，第二步浮选脱除并回收尾灰中Pb、Zn等重金属。浮选后残灰的体积和毒性将大幅度降低，可考虑直接填埋处置，富碳精灰可考虑再利用。研究发现两步浮选处理可实现飞灰的低成本、无害化处理及资源化利用。