氮掺杂碳纳米管对嗜酸细菌氧化废弃线路板中零价金属的催化作用及其机理研究

Waste printed circuit boards(PCB) were the excellent secondary resources of E-waste. Zero-valent metals in PCB could be leached by microbial method, which was environmentally friendly. The method was limited to be used in industrial applications because the time is so long that bacteria leaching metals from PCB. Therefore, It was critical to improve the ionization efficiency of zero-valent metals from PCB in the process. Nitrogen-doped carbon nanotubes(NCNTs) as the representative of the nanomaterial had the characteristics of the catalytic reaction. If NCNTs was added to the solution that acidophilus bacterial leaching metals from PCB, it might catalyze the dissolution rate of zero-valent metals from PCB. So the amount and method of NCNTs applied to the bioleaching solution was studied, then the efficiency of metal dissolution and electron transfer rate were analyzed during the process. The mechanism of acidophilus bacteria leaching zero-valent metal of waste PCB was explored through fluorescence and isotopic tracer. And the effect of NCNTs on bacteria growth, adsorption on the surface of PCB and their action mechanism was discussed. The heat transfer efficiency of the heating process in a large volume solution (pilot levels), and the dissolution efficiency of metals from PCB were observed when NCNTs was added. Through these series experiments, theoretical support will be provided for biological methods used for the industrial application recycling metals from waste PCB.

废弃电路板（PCB）是电子废弃物中优质的"二次资源"，环境友好的微生物方法能应用于废PCB中零价金属的资源化，由于菌种浸取PCB中金属的时间较长使得生产周期长的原因限制了该方法的工业应用，因此提高该过程中零价金属的离子化效率是关键。氮掺杂碳纳米管(NCNTs)有催化氧化还原反应的特性，本项目拟在菌种浸取废PCB的反应体系中添加NCNTs，研究NCNTs添加量及其方式对嗜酸细菌氧化PCB中Cu等零价金属的催化特性，分析该过程中金属溶出效率、电子传递及溶解氧消耗速率；采用荧光和同位素示踪方法探索菌种浸取废PCB中金属的作用，研究NCNTs对该过程中菌种生长、在PCB表面吸附及其作用的影响，并采用荧光定量PCR分析菌种活性稳定性，解析其机理; 在大体积（中试级别）条件下观测加热过程中NCNTs对溶液传热效率的影响、及PCB中金属的溶出效率，为该方法的工业应用提供理论支撑。

废弃线路板(PCB)是电子废弃物中资源化价值高、处理难度大的重要部件，含有铜等多种金属。嗜酸氧化亚铁硫杆菌（Acidithiobacillus ferrooxidans，以下简称嗜酸细菌）浸铜效率低问题限制了其大规模工业化应用。本项目对氮掺杂碳纳米管(NCNTs)在嗜酸细菌浸出PCB中零价金属过程中的影响进行了试验研究和理论分析。提出了将NCNTs以直接添加和涂布电极（碳布、碳棒）两种方式对嗜酸细菌浸铜等零价金属。NCNTs和嗜酸细菌相容性试验研究表明，两种添加方式下嗜酸细菌都可以良好生长。NCNTs的最适添加量试验研究发现，在直接添加方式下，其最适添加量为0.8g/L培养液，在涂布电极（碳布、碳棒）的方式下，其最适添加量分别为0.352g/L和0.4g/L培养液，与未添加组相比，PCB中铜浸出率都提升了20%以上。对嗜酸细菌浸出液的残渣分析表明，两种添加方式下，其浸出残渣中晶型沉淀都不一致，对照处理中形成了KFe3(SO4)2(OH)6、直接添加NCNTs处理中形成了FeCl3•6H2O、而涂布NCNTs电极处理中形成了(NH4)Fe3(SO4)2(OH)6，表明NCNTs影响嗜酸细菌浸出液残渣中晶型沉淀的形成，进而影响嗜酸细菌冶金的效率。NCNTs循环利用的试验研究表明，两种添加方式下NCNTs都可以进行循环利用。同时，采用石墨烯进行同样的试验进行对比研究，主要结果与NCNTs的系列试验结果一致。因此，研究表明采用NCNTs或石墨烯能对嗜酸细菌浸出PCB中零价金属Cu时发挥催化作用，提升浸出效率，且性能稳定。