Metals Recovery And Electro-Oxidation Performance Of Carbon-base Composite Electrode Materials

The cycle of iteration and upgrading of electronic products is getting shorter and shorter in present information age,a large number of electronic devices are eliminated and become electronic wastes(E-waste)and the toxic substances contained in them will cause seriously damage to the ecosystem.Considering the rich non-ferrous metal resources in E-waste,how to recycle and reuse the non-ferrous metals in E-waste efficiently is the key to solve the current problems of resource shortage and public health.Electrochemical method owning the advantages of simple operation,process regulation,good selectivity and economic and environmental friend,could be applied to separate and purify the target metals,which has important scientific research meaning and wide application prospects.In the process of electrochemical system establishment,the design of electrode materials is directly impact on the performance of metal recovery.In the field of metal recovery,the target metal ions could be selectively captured by means of the redox state presented by the specific functional groups or molecular structures in the organic/inorganic redox-active materials under electrochemical mediation.Furthermore,the metals could be recycled as electrocatalysts for secondary use.Based on the abundant active sites in polymetallic catalysts and the accelerated electron transfer rate in the electrochemical reaction process and catalysts synthesized with Ewaste as raw materials,the electrochemical systems with high anode electro-oxidation and cathode electro-Fenton performances were constructed for the degradation and transformation of organic matter.In this paper,for the common electronic waste in life,the designs of carbon cloth/polyaniline composite electrode material(CC/PANI)and carbon cloth/zinc potassium ferricyanide composite electrode material(CC/KZHCF)are used to recycle gold from the waste central processing unit(CPU)and cobalt from the waste lithium cobalt acid battery(LiCoO2),respectively.Gold-copper alloy/carbon cloth composite electrode material(CuAu/CC)and nickel-cobalt-manganese/carbon cloth composite electrode material(NCM/CC)were designed and synthesized from waste CPU and waste NCM ternary lithium battery for electrochemical degradation of bisphenol A(BPA)and electrochemical oxidation of ethylene glycol(EG).The metal recovery mechanism and electrocatalytic reaction mechanism behind these materials are discussed in detail here.The main contents of this paper include:1.Based on the traditional recovery of single metal,a carbon cloth/polyaniline composite electrode//carbon cloth(CC/PANI//CC)asymmetric electrochemical system was innovatively designed for simultaneous separation and recovery of gold and copper in mixed components.Attributed to the unique positive-charged property of polyaniline redox-active polymer under electrochemical mediated,it could efficiently and selectively adsorb[AuCl4]-ions under electrostatic action and then be reduced to gold elemental by rich reductive nitrogen-containing functional groups for recovery.Moreover,the composite material has excellent recycling characteristics after being washed by thiourea.At the same time,the carbon cloth was used as the cathode,and the copper ions in the mixed solution were reduced and deposited on the surface of the carbon cloth,which was then recovered by simple ultrasonic stripping and elution.This electrochemical system could realize the separation and recovery of nearly 100%of the gold and copper in the actual waste CPU leaching solution,and the purities of gold and copper reaches 23 carats and 94%,respectively.This work has proved the feasibility of separating recovered metals from multi-component systems and has important guiding significance in the field of precious metal recovery and heavy metal removal.2.Based on the unique face-centered cubic lattice structure and open molecular framework of Prussian blue analogue materials,carbon cloth/zinc potassium ferricyanide composite electrode(CC/KZHCF)was synthesized by electrodeposition and hydrothermal method,and used as the working electrode for the selective extraction of cobalt ions from waste LiCoO2 batteries.By first converting Co2+ into Co(NH3)63+with a smaller hydration radius make it easier enter the framework of KZHCF and occupy the original alkali metal ion(K+ion)site in the structure.Under the best conditions,the electrosorption efficiency of Co ionreached 98.6%.Then the adsorbed Co ions could be desorbed from the electrode by a simple voltage reversal treatment.Furthermore,lithium and cobalt in the solution were used to produce high-purity lithium carbonate(Li2CO3)and cobalt hydroxide(Co(OH)2),respectively by electrosorption/desorption and chemical precipitation,which could be used as raw materials for the fabrication of LIBs directly.This work provides meaningful guidance for the downstream recycling industry of power batteries.3.In order to further explore the electrocatalytic performance of the recovered metals,on the basis of the previous two chapters,a bimetallic catalyst derived from Ewaste with a controlled ratio of gold and copper was successfully prepared by electrodeposition on the surface of carbon cloth using waste CPU as raw material.The CuAu/CC composite electrode material could be directly used as an electrode for the removal of(bisphenol A)BPA in the electro-Fenton system.Due to the bimetallic cocatalytic effect and charge transfer effect,oxygen on the electrode surface was reduced to hydrogen peroxide and then decomposed into active free radicals with strong oxidation ability for the oxidation of BPA.The results showed that the removal rate of BPA in the electro-Fenton system reached 99.5%and the total organic carbon(TOC)dropped to 64.2%under the optimal operating conditions,indicating that CuAu/CC has good electro-Fenton performance.The work imovatively prepared the alloy catalyst with E-waste as raw material while avoiding the disadvantage of low activity when using single metal catalyst,and provided valuable guidance for realizing the goal of"treat waste with waste".4.Considering the abundant nickel,cobalt and manganese metals resources of waste ternary lithium battery,the multi-component metal catalyst was successfully prepared by hydrothermal method.Based on the advantages of rich reactive sites brought by the nanoflower-like structure of nickel-cobalt-manganese ternary catalyst and the synergistic catalysis of three metals,the prepared nickel-cobalt-manganese terephthalate catalyst/carbon cloth composite electrode material(NCM/CC)could be used as anode to produce formic acid by electrochemical oxidation of ethylene glycol(EG),one of the waste PET(polyethylene terephthalate)plastic hydrolyzed products,and has high selectivity and Faraday efficiency.The formation of formic acid molecules was accelerated by the binding of hydroxyl radicals(·OH)generated in situ on the surface of the anode material with EG molecules.In addition,during the hydrothermal synthesis of the catalyst,the lithium ions which did not participate in the reaction in the precursor solution were recovered in the form of Li2CO3.At the same time,another important industrial raw material terephthalic acid could be obtained through the hydrolysis treatment of PET plastic in the process of waste PET recycling.The work achieves the green development goal of "turning waste into treasure".