| In view of the increasing awareness of environmental protection,the sharp increase in waste printed circuit boards(WPCBs)and the lack of basic research and applied technologies related to green recycling,there is an urgent need to develop a green process and method for recycling WPCBs.In this thesis,based on the deeply analysis of the structure and composition characteristics of WPCBs and the major current international technical methods used to deal with WPCBs,combined with the inherent advantages of ionic liquids as green environmental solvent,research idea that WPCBs was treated and recycled by functionalized ionic liquids pyrolysis was put forward.Several functionalized ionic liquids with chemical stability in high temperature adapted to pyrolysis processs was designed and synthesised,on the basis of effective increase in the pyrolysis capacity and the ability to leach the metals of ionic liquids in WPCBs,the times of recycling and stability of ionic liquids were increased in a large scale,the recycling operating costs of WPCBs were reduced.The relationship between the structure and composition characteristics,the tested temperature,the kind and content of various raw and the leaching amount of the metals in the ionic liquids in WPCBs were studied.The mechanism of the pyrolysis and leaching of the metals in the ionic liquids were discussed to optimize pyrolysis leaching process and methods of ionic liquids,which formed a green recycling process and method of metals in WPCBs.The main research contents and conclusions are as follows:(1)Combined with reaearch idea,several kinds of imidazolium-based functional ionic liquids containing alkyl,sulfonic acid and carboxymethyl functional groups were designed and synthesized by indirect synthesis method by selecting appropriate materials with specific functions.The structure of the synthesized ionic liquids were characterized by infrared spectroscopy,nuclear magnetic resonance spectroscopy and elemental analysis.The influence of the experimental temperature in the chemical stability of the ionic liquid was studied by thermogravimetric analysis.(2)In terms of the structure and composition characteristics of the solder in WPCBs,the solder was recycled by hot-melting using [BMIM][BF4].The structure and composition characteristics of WPCBs were studied,meantime,the technological parameters of the hot-melt leaching were determined and the influence of the temperature of WPCBs in the ionic liquid in the recovery of the solder was investigated.The results showed that the solder on WPCBs was hot-melted under mechanical stirring at 200 °C.The process not only kept the solder melt off and maximized to protect the WPCBs substrate from thermal cracking,the recovery rate of solder reached 90 % or more.(3)Using acidic functional ionic liquids for the thermal leaching recovery of the metals in WPCBs,the effects of different kinds of ionic liquids and different experimental conditions on the yield of metal were investigated.The structure and composition characteristic,the tested temperature,the kind and content of the various added raw materials and the leaching relationship of metallic materials in the ionic liquids of WPCBs were studied.The results showed that the recovery rate of metals in WPCBs of 1-carboxymethyl-3-methylimidazolium bisulfate functionalized ionic liquid([CM-MIM][HSO4])was much higher than others.The excellent program was obtained with access to univariate analysis: the concentration of acidic functional ionic liquid was 90 %,the size of WPCBs particle was no less than 0.5 mm,the solid-liquid ratio was 1:20,the temperature was 80 oC,the reaction time was 120 min and the oxidant content was 15 %(v/v).The recovery rate of the metal under the process was 31.63 %.Through the electron probe in the energy spectrum analysis,that reduced metal contained 98.33 % of the copper element was proved.(4)With the design of L25(56)orthogonal experiment,the pyrolysis leaching process and method of functional ionic liquid was optimized.Considering the influence of different experimental factors in the yield of metals in WPCBs comprehensively,the priority order of factors affecting the recovery rate of the metals in WPCBs were obtained by the intuitive analysis method: the concentration of functionalized ionic liquid,the solid-liquid ratio,the reaction temperature,the reaction time,the size of WPCBs particle and the oxidant content successively.The optimal scheme was determined: the concentration of acidic functional ionic liquid was 90 %,the WPCBs particle size was less than 0.5 mm,the solid-liquid ratio was 1:30,the reaction temperature was 70 oC,the reaction time was 150 min and the oxidant content was 5 %(v/v).The recovery rate of the metal with the process was 38.49 %.The electron probe in the energy spectrum analysis revealed that the recovered reduced metal contained 99.57 % of the copper element.(5)Considering the actual industrial application conditions such as production cost and operation comprehensively,a green recycling technology and method that the metals in WPCBs was recycled was formed by combining with the recycling scheme and the optimized pyrolysis process,the optimal process parameters of the recovery technology of metals in WPCBs were obtained: the concentration of acidic functionalized ionic liquid was 70 %,the size of WPCBs particle was no less than 0.5 mm,the solid-liquid ratio was 1:30,the temperature was 70 oC,the reaction time was 150 min,the oxidant content was 5 %(v/v).The recovery rate of the optimal solution is 35.74 %.Through the electron probe in the energy spectrum analysis,that the reduction of metal contained 98.31 % of the copper element was proved. |
PDF Full Text Request