| Printed circuit board (PCB) is an important component in almost any electronicproducts. In2006, China PCB production and sales had surpassed the United States,Europe and Japan, becoming the largest producer in the world. The total annualcapacity of PCB production in China reached about200,000,000m2. As a result, alarge amount of high copper-containing spent etchant was generated. According to-statistics,6,000tons or more spent etchant are generated every day in China’s PCBfactories. If they can be properly recycled, about200,000tons of copper would havebeen recovered each year, alleviating environmental pollution and gaining a benefit ofmore than10billion Yuan RMB. Different on-site electrolytic regeneration methodshave been researched and developed, in order to achieve metal recovery and etchantrecycling simultaneously so as to substantially reduce the amount of required freshetchant and other chemicals, while eliminating bulk hazardous waste shipped off-sitefor reclamation. However, electrolytic etchant regeneration has not been widelyadopted so far for technological and/or economical reasons.To realize safer, cleaner and yet economically competitive PCB production, anovel electrolytic process for simultaneous cupric chloride etchant regeneration andcopper recovery is proposed and investigated in this dissertation. A three dimensionalanode made of carbon felt is used to oxidize cuprous ions while avoiding oxygen andchlorine evolution. The limiting current of Cu(I) oxidation on carbon felt electrode ismuch higher than that on platinum electrode because of the large real surface area ofcarbon felt. The carbon felt electrode also inhibits gas evolution, as indicated by anobviously higher onset potential of gas evolution reaction in contrast to Pt electrode.The proposed electrolytic regeneration method enables effective Cu(I) oxidation atlow enough over potential that noticeable gas evolution can be avoided, thuseliminating the need of complex safety measures to deal with hazardous chlorine.Following the success of above mentioned preliminary feasibility verification,electrolytic cell scale-up has been carried out. Computational fluid dynamicssimulation is employed to study the flow patterns in the electrolytic cell and to aid thedesign of fluid distributor. A new cell as11times the volume and electrode area as theinitial small cell has been build and tested. The performance of the new cell is almost as well as the small cell, with only a little higher cell voltage caused by increasedcontact resistance.Restoration of worn carbon felt anode have also been carried out for the firsttime, in order to curb the deterioration of anode performance. The carbon feltaccumulatively worn for100h is restored under a cathodic potential of-3.2V inNaOH electrolyte to reduce the oxygen and chloride containing species formed on thefelt surface during etchant regeneration. Fortunately, roughly half of the decrease incurrent density can be regained through the simple restoration procedure.Efforts have also been made to further improve the performance of carbon felt,by thermal or Iridium modifications. While a heat treatment of the carbon felt at400C makes little difference as compared with the pristine carbon felt, Irmodification of the carbon felt significantly increases the limiting current density ofCu(I) oxidation and results in even lower cell voltage at the same Cu(I) concentration.The stability of Ir modified carbon felt is studied by using scanning electronicmicroscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-raydiffractometry (XRD). The results indicate that the loss of iridium from carbon felt ismainly during the first25hours of electrolysis process. The composition of Ir speciesremains almost invariant from the first25hours to75hours of Cu(I) oxidation.Interestingly, the75hours worn Ir modified carbon felt shows even betterelectrochemical performance, due to deepened Ir oxidation. |
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