| Electrical and electronic waste (e-waste) has been regarded as the fastest increasingsolid waste steam in global generation amount. It is directly derived from anthropogenicutilization and consumption, and it has become currently one of focuses in environmentalprotection because majority of e-waste contain considerable valuable materials (e.g.nonferrous metal) and can severely pose potential environmental risk from heavy metalsand persistent organic pollutants. Recycling of e-waste is supposed as the most effectiveapproach to solve e-waste problem and maintain the sustainable development ofnonferrous metal industry. Printed circuit boards (PCBs) and rechargeable lithiumbatteries (RLBs) are quite indispensable parts to function most electrical and electronicequipment. Thus, recycling for typical parts such as waste PCBs and spent RLBs is thekey core in e-waste management.In order to measure the recyclability and recycling difficulty of e-waste,mathematical models were established based on the existing Statistical EntropyFunction and newly defined rules of grade determination. The obtained resultsindicate that e-waste recycling can be graded into three levels of difficulty, withmost types of e-waste at the moderate level, and that comparing to other e-waste,waste PCBs and spent RLBs are extremely difficult to deal with towards resourcerecycling and environmental improvement. And they are much similar in physicalstructure and manufacturing process, using solder or binder to tightly link othercomponents. In order to open the link or inter-connect, inverse manufacturing methodwas employed to dissolve the solder or binder in appropriate heat medium. Therefore, weused water-soluble ionic liquid and Fourier law of heat conduction and determined theoptimal recycling process of tin solder and aluminum. The results obtained from theoryanalysis and experiment verification reveal:1) the dismantling rate of waste PCBs canreach90%and the recycling rate of tin solder can exceed90%, while heating temperature,retention time, and rotation are controlled at250℃,12min, and45rpm, respectively,and2) the recycling rate of aluminum foil can reach99%and its purity can exceed95%,while heating temperature, retention time, and rotation are controlled at180℃,25min,and300rpm, respectively. Oxalic acid was adopted to leach and recycle cobalt and lithium from scrapspent RLBs (containing lithium cobalt oxide, aluminum, copper, and iron),verifying this process can significantly shorten conventional spent RLBs. In caseof150min of retention time,95℃of heating temperature, and400rpm ofrotation, the average recycling rate of cobalt and lithium was97%and98%,respectively. Simultaneous heat transfer, chemical reaction, and mass transferoccur during this leaching process, which belongs to liquid-solid non-catalyticreaction. In contrast to film diffusion, the leaching process was mainly supervisedby chemical reaction, whose kinetics equation was1(1)1/30.034t0.018(ω is consumption ratio of oxalic acid, and t is reaction time (h)). The reactionorder and conditions of scrap spent RLBs and oxalic acid were determined,faciliating the optimal recycling process development for cobalt and lithium.The obtained models of measuring the recyclability for e-waste cancontribute to future recycling and management of e-waste and its parts. Thedeveloped processes recycling nonferrous metals (including tin, aluminum,cobalt, and lithium) supply a technological foundation and theory supporting forindustrial recycling of waste PCBs and spent RLBs. |
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