胞外多聚物促进重金属危废有价金属生物沥浸的作用特性和分子机理

Recovery of valuable metals from various heavy metals-bearing hazardous wastes is of very importance from the viewpoint of both environmental protection and resource recycle. Extraction of valuable metals from heavy metals-bearing hazardous wastes by bioleaching has been receiving growing concerns worldwide owing to its green, safe, low-cost and eco-friendly nature. However, because the metals-bearing hazardous wastes are generally characteristic of high alkalinity and/or high toxicity which seriously endanger the growth and activity of leaching cells, the pulp density of bioleaching is always 1.0% (w/v) or lower, meaning a smaller bioleaching capacity and a worse practical application potential. Previous preliminary research indicated that extracellular polymeric substances (EPS) shows a unique function in preventing the leaching cells from being harmed by the high alkalinity/high toxicity, exciting the leaching cells to produce more active substances for the metals extraction, enhancing adhesion between the leaching cells and solid wastes, thereby promoting bioleaching performance at a higher pulp density. In this proposal, four kinds of typical heavy metals-bearing hazardous wastes, i.e. obsolete electric vehicle lithium ion batteries, disabled nitrogen-removed catalyst, electroplating sludge and pickling sludge, were chosen to explore the enhancing effect and molecular mechanisms of the EPS on the bioleaching of metals-bearing hazardous wastes. For the purpose, four aspects will be conducted: 1) to examine the formation behavior of EPS in the process of bioleaching and the relationship between EPS and metals extraction efficiencies; 2) to investigate the enhancing effect of added EPS on the extraction of valuable metals from various metals - bearing hazardous wastes and its dynamics and thermodynamics; 3) to reveal the molecular mechanism and interface process of added EPS to enhance bioleaching performance; 4) to develop efficient technology and parameters for overproduction of EPS via adding organic carbon sources to improve the bioleaching efficiency.

鉴于重金属危废资源化利用所展示的巨大经济收益和环境效益以及安全、绿色、节能的自养生物沥浸技术所展现的巨大应用潜力，着眼于重金属危废生物沥浸技术实际应用所面临的高碱性/高毒性这一共性难题的解决以及前期研究所昭示的EPS抵御高碱性/高毒性的卓越性能，本项目选择四种典型重金属危废，即废旧动力锂电三元材料、失效脱硝钒钛催化剂、电镀污泥和酸洗污泥，研究不同类型重金属危废生物沥浸过程EPS生成特性及其与金属溶释行为的关系，考察提纯EPS投加对不同重金属危废有价金属溶释的促进效应及其动力学和热力学，揭示提纯EPS促进不同重金属危废有价金属溶释分子机理和界面过程，确立激发沥浸过程EPS超量生成关键技术及提高有价金属溶释效能。项目研究对于重金属危废的环境污染控制、高价/稀贵金属资源的循环和可持续利用以及生物沥浸技术的发展都具有重要意义。

鉴于重金属危废资源化利用所展示的巨大经济收益和环境效益以及安全、绿色、节能的自养生物沥浸技术所展现的巨大应用潜力，着眼于重金属危废生物沥浸技术实际应用所面临的高碱性/高毒性这一共性难题的解决以及前期研究所昭示的EPS抵御高碱性/高毒性的卓越性能，本项目选择四种典型重金属危废，即废旧动力锂电三元材料、失效脱硝钒钛催化剂、电镀污泥和酸洗污泥，研究不同类型重金属危废生物沥浸过程EPS生成特性及其与金属溶释行为的关系，考察提纯EPS投加对不同重金属危废有价金属溶释的促进效应及其动力学和热力学，揭示提纯EPS促进不同重金属危废有价金属溶释分子机理和界面过程，确立激发沥浸过程EPS超量生成关键技术及提高有价金属溶释效能。主要得到了以下结论：对于废旧三元材料，目标金属Ni、Co、Mn的溶释效率与EPS浓度存在显著的正相关关系。接触角、表面能测试计算表明，EPS可以提高材料的亲水性，促进材料和沥浸液的润湿接触，更利于金属的溶释。Fe3+和 Fe2+能够增加静电引力进而促进沥浸细胞与沥浸材料之间的吸附，但甲醇和尿素由于能够破坏疏水力，进而抑制沥浸细胞与沥浸材料之间的吸附。疏水力在沥浸菌株与三元材料的吸附中起着主导作用。外加EPS的生物沥浸体系中的腐蚀电流密度增大，电极表面腐蚀速率加速，电化学极化电荷转移电阻（R1）和控制废旧三元材料溶蚀的传质阻力（R2，Warburg阻抗）共同的降低，体系中发生反应的吉布斯活化自由能降低，促进了金属溶释。在废催化剂的生物沥浸过程中，EPS主要成分为类腐殖物质(＞70%)，次要成分为类蛋白 (＜30%)。在低固液比(5.0%或更低)时，总EPS和腐殖质类物质在整个沥浸过程中均呈增长趋势;当固液比为7.5%或更高时，总EPS和类腐殖质含量呈下降趋势。Co的浸出效率与腐殖质类物质有显著相关性。EPS总量和腐殖质类物质与Mo的生物浸出效率均存在显著关联，但腐殖质类物质对Mo的生物浸出影响较大。腐殖质类物质对浸出过程的影响较大。