废覆铜板分选残渣生物脱毒工艺优化及机理

Cu extraction from waste copper clad laminate sorting residue in a two-stage bioleaching process:Process optimization and mechanism

废覆铜板分选残渣量大,残留铜质量分数约为1%,潜在利用价值高.为了获得废覆铜板分选残渣生物浸出脱毒工艺最优条件及探明其生物浸出相关机理,首先采用Box-Behnken响应曲面法设计三因素(参数因子包括初始pH值、固形物含量和Fe浓度;响应值为铜浸出率)三水平共计17个实验的优化实验方案.响应面多项回归拟合分析指出:铜浸出率回归模型与实际试验拟合性较好,实验误差较小,对废覆铜板分选残渣中铜生物浸出过程优化具有一定参考性.在最优化条件下(初始pH值为1.65、废覆铜板分选残渣投加量300 g·L^(-1)和Fe^(2+)质量浓度为6.13 g·L^(-1))经过4 h生物浸出获得(92.2±0.27)%的铜浸出率.其次,废覆铜板残渣生物浸出脱毒放大改进实验中(100 L搅拌槽):增加曝气和搅拌,同时外加酸调控体系pH值<2.5,延长浸出至6 h,铜最大浸出率>98%,浸出渣中铜残留质量分数≤0.02%.未反应缩核动力学模型显示残渣中铜生物浸出过程受界面传质和固体膜层内扩散混合控制.综上所述,废覆铜板分选残渣中的铜主要通过Fe^(3+)氧化和H^(+)攻击溶出;嗜酸氧化亚铁微生物持续氧化Fe^(2+)→Fe^(3+),不仅降低了总铁消耗量,也促进了残渣中铜的释放.研究结果将为废旧电子电器绿色资源化再生利用提供理论支撑.

Much waste copper clad laminate sorting residue is generated from the flotation process of recovering copper resources from waste printed circuit boards.The improper treatment and disposal of waste copper clad laminate sorting residue harms the environment and human health.According to the National Hazardous Waste List(2021 edition)of China,this waste belongs to HW13(900-451-13)hazardous waste.The sorting residue contains approximately 1%copper,which is similar to the average copper grade of 0.8%in China.Therefore,this residue is an important copper renewable resource and has a high potential for copper recycling.To optimize the effective factors,including the Fe^(2+)concentration,initial solution pH value,and pulp density,and clarify the mechanism during the bioleaching process of waste copper clad laminate sorting residue,a Box-Behnken design of response surface methodology was first used,and a scheme consisting of 17 experiments was designed in the present study.Through the multiple regression fitting analysis of experimental results,a quadratic polynomial regression model was established.The regression model showed high reliability and simulation accuracy and was then used to optimize the bioleaching process.Under the optimal conditions(6.13 g·L^(-1)Fe^(2+),initial leaching solution p H value of 1.65,and pulp density of 30%),92.2%maximum Cu extraction was obtained.Then,a modified scale-up bioleaching experiment in a 100-L stirred tank was performed.The results indicated that the maximum copper recovery reached 98%,and less than 0.02%of copper was detected in the bioleaching residue after 6 h of bioleaching because of the improved bioleaching operating conditions in the 100-L stirred tank,including slowly adding the sorting residue,additional stirring(200 r·min^(-1)),aerating(20 L·h^(-1)),and controlling the bulk pH value(solution pH value<2.5 adjusted with 50%(v/v)H_(2)SO_(4)).Leaching kinetic data described by a modified shrinking core model indicated that interfacial transfer and diffusion across the solid film layer controlled the copper dissolution kinetics.In conclusion,copper in the sorting residue was dissolved primarily by Fe^(3+)oxidation and secondarily by H^(+) attack throughout the bioleaching process.Notably,the continuous regeneration of Fe^(3+)by an iron-oxidation microbial consortium led to more Fe^(3+)distributed across the solid film layer of residual iron/calcium compounds and accumulated on the reacted core,which not only reduced total iron consumption(particularly Fe^(3+))but also substantially improved copper extraction from waste copper clad laminate sorting residue.These findings should have important implications for the green recycling and reuse of waste printed circuit boards and other waste electronic appliances.