| The rapid development of the electronic industry leads to the quick replacement of electronic products and asignificant increase of waste electric and electronic equipment(EEE).As an important component,printed circuit board(PCB) is also wasted largely by waste EEE.PCB is composed of plastic,refractory oxides and metals such as Au Ag Cu Pt and so on.The main economic driving force for the recycling of waste PCB comes from the recovery of metals,particularly precious metals like gold.In this thesis,firstly the characteristics and the methods of recycling waste PCB at home and abroad were summaried.After emphatically introducing the hydrometallurgical processes,the urge of exploit an non-cyanide process for gold recovery with non-toxic reagent,high recovery rate and no pollution to environment was emphasized.Based on the results of gold recovery in related fields and the summarization of the research methods used by the predecessors,the"leaching gold by iodide process and extracting gold by electrodeposit process"combined process was chose to extract gold from waste PCB.So the objective of this research is to offer a more economical and environmentally-friendly process for gold recovery from waste PCB.The research described in this thesis can mainly be devided into three parts, analysis of the component and content of metals in waste PCB,gold leaching from waste PCB by iodide process and gold extracting from iodide leaching solution by electrodeposit process.Part one:The element component and content of metals in PCB were determined by FAAS and ICP-AES methods respectively.Results shows the content of gold 0.324mg/g.Part two:Leaching gold from pretreated powder of waste PCB by iodide process.First,the composition characteristic for gold leaching systems,the thermodynamic criterion of oxidants selected for gold leaching systems and the relationships between oxidants and ligands were analyzed in details.Second,the thermodynamic criterion of oxidants selected for gold iodide leaching systems were analyzed in details.The gold leaching in the form of AuI2-could be performed spontaneously provided that the standard electrode potential of oxidants is larger than +0.561V.The gold leaching could be performed spontaneously in iodine-iodide system provided that the concentrations of I- and I3- are changed, while the electromotive force(EMF) of the reaction is positive and the reaction free energy is negative.Third,according to these theoretic analyses,the author Leached gold from pretreated powder of waste PCB in iodine-potassium iodide system with hydrogen peroxide as the assistant oxidant.Through single-factor conditional experiment and orthogonal experiment,The most optimized qualifications of iodide leaching gold from waste PCB are elicited:iodine concentration 1.1%,n(I2):n(I-)=1:10,H2O2 concentration 1.5%,the leaching time 4hr,the ratio of solid to liquid 1:10,leaching gold at normal temperature(25℃),pH=7.Gold leaching recovery can reach at about 97.5%.Leaching gold from pretreated powder of waste PCB after calcining treatment was analyzed.Although most plastic was wiped off,it was not beneficial to the gold leaching,so the calcining treatment process could be left out.Part three:Extracting gold from waste PCB's iodide leaching solution by electrodeposit process.First,the electrodepositing gold process was theoretically analyzed.The reaction of gold electrodepositing process is actually composed of AuI2- reducing,I- oxidating and water electrolyzing.Second,under these theoretic analyses,the electrolysis cell with ion exchange membrane was used to extract gold from waste PCB's iodide leaching solution. Through electrolysis experiment,the most optimized qualifications of electrodepositing gold from waste PCB's iodine leaching solution were elicited:in the cell carbon rods(cathode) and titanium plate(anode) were used as electrode,the cell was partitioned by anion exchange membrane,iodine concentration in anode solution was 0.1%～0.8%,n(I2):n(I-)=1:10,cell voltage was 10～14V,gold concentration in cathode solution was 15mg/L～50mg/L,electrolyzing time was 1～4hr.The electrodepositing rate of gold was bigger than 95%.Third,guaranteeing the high electrodepositing rate of gold,the influences of iodine concentration in anode solution and gold concentration in cathode solution on the electrodepositing rate of iodine were analyzed.The iodine concentration in anode solution had some influence on the electrodepositing rate of iodine,but generally,the electrodepositing rate of iodine was comparatively small.After electrolytic reaction, the method directly using the anode solution to leach gold from pretreated powder of waste PCB was tried.Experiment result proved that the method was feasible and good electrodepositing rate of gold could be got.Conclusively,the"leaching gold by iodide process and extracting gold by electrodeposit process"combined process combines the advantages of iodide process such as high leaching rate of gold,non-toxic and recovered reagents,with the advantages of electrodeposit process such as no added reagent,electrodeposited gold with high purity,simple technological process etc.Applying this combined process to extract gold from waste PCB is a feasible,economical and environmentally-friendly method for gold recovery from waste PCB.
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