Research On Reutilization And Flotation Kinetic Model Of Waste Printed Circuit Boards

Study on waste electrical and electronic equipment (WEEE) and the reutilization of waste printed circuit boards (PCBs) have the important significance and application values, which can not only achieve recycling of secondary resources, but also prevent environment pollution. The metals in PCBs are recycled with a flowsheet of wet impact crushing——flotation in the dissertation. In China, the subject of PCBs flotation is novel at present.Firstly, the relationship among the operational factors of the wet impact crushing was studied. With the Design-Expert software, the predicting equation of the operational factors to the yield in -0.5mm fraction was derivated in theory.The natural hydrophobic flotation test on -0.5mm crushed products of the waste PCBs was undertaken, using Design-Expert software to optimize the various experimental parameters (agitation speed, aeration rate, temperature, solid concentration), and the sink yield was up to 71.6743%; the grade was up to 28.7950%; the recovery rate was over 90%. In theory, the predicted models about yield, grade, recovery rate, and enrichment ratio of the sink were deducted. Based on the models, the reagent flotation was studied with selecting four collectors (new type collector 9858, new type collector 9883, butyl dithiophosphate and butyl xanthate) and four frothers (MIBC, new type frother 9862, sec-octyl alcohol, and 2# oil). When the new type collector 9858 and frother 9862 were chosen and mixed to be used in the experiments, the sink yield was up to 64.757%, the metal grade was 25.377%, the recovery rate was 98.438%, and the enrichment ratio was 1.520. Synthesizing the separation indicators, the collector and the frother worked effectivly.Using four usual flotation kinetic models of traditional minerals, the flotation kinetic models for waste PCBs flotation depending on the natural hydrophobicity or reagent were studied. The flotation kinetic models which were achieved in five different conditions were conducted through the experiments. The theoretical foundation was built for optimization of the floation process operation, simpliying the flotation flowsheet.The crushed and flotation products were studied by the fractal. And the results showed that the variation of size fractal in the floation was fitted in with the polynomial equation:D=At~5+Bt~4+Ct~3+Dt~2+Et+1.292 A、B、C、D、E hereby are constants, t is the processing time, D is represent for the dimension of fractal.The sorting results of the flotation of waste PCBs were analyzed by gray theory, and the sorting results of multi-factor test were analyzed by gray relevance theory. The results show that the correlation of sink yield, sink grade, metal recovery and enrichment ratio affected by operation factors from large to small is: aeration rate, temperature, solid concentration, agitation speed. Namely the order of the factors on the influence degree of the sorting index is aeration rate, temperature, solid concentration, agitation speed. A gray model between the operation parameters and the separation effects of the flotation of waste PCBs were established by applying the gray modeling theory.For the flotation of waste PCBs, the results of the study show that the flotation process is simple and effective, and the separation effect is better. It provides a new processing method for electronic waste recycling and also broadens a new application for flotation.The thesis contains 85 figures, 43 tables and 192 references.