| Tuning Fork Crystal Resonators(TFCRs)are one of the most important electronic components.TFCRs are widely used in various electronic products for its small size,stable frequency and low cost.With the upgrading and replacement of electronic products,a large amount of waste TFCRs have been produced.On the one hand,the waste TFCRs contain a variety of metals,such as iron,aluminum and gold,and recycling waste TFCRs can not only get high economic benefit but realize the sustainable target with “3R”.On the other hand,the waste TFCRs also contain organic resins which are difficult to separate and degrade and hinder the efficient recovery of the metals,so that the reasonable treatment can improve the efficiency of metal recovery and reduce the harm of the environment and human health.Hence,it is urgent to develop a set of recycling process of waste TFCRs with efficient and green.This study proposed a combined process with mechanical separation-vacuum pyrolysis-selective leaching to recover the metal of iron,aluminum,gold and to remove organic matter in waste TFCRs.First,analyzing the structure distribution characteristics and composition characteristics of the TFCRs,the waste TFCRs were used the mechanical separation with the order of crushing,magnetic separation,screening and vortex sorting separation to recover iron and aluminum.The iron almost recovered completely and the recovery grade was 99.06%,and the recovery efficiency and grade of aluminum were 91.16% and 98.52% respectively.The optimum parameters were at the condition of feed rate 1.1 m/s and drum speed of 314 rad/s.Then,the organic materials of waste TFCRs were degraded by vacuum pyrolysis.Three independent variables of vacuum pyrolysis experiment were investigated.We used the response surface method to know that the optimal pyrolysis parameters were the pyrolysis temperature of 600 °C,the reaction time of 45 min and the system pressure of 1500 Pa.Under this condition,the conversion rate of organic matter was 84.63%.The contents of pyrolysis products under optimized conditions were analyzed.The mechanism of pyrolysis path of organic materials in TFCRs was speculated.Next,the metal gold was enriched and purified by the controlled potential selective chlorination of base metal and gold,methyl isobutyl ketone extraction and oxalic acid reduction.The theoretical equilibrium of controlled potential chlorination was analyzed and determined the immersion gold potential at 1.10±0.01 V.The effects(temperature,time,concentration of sodium chloride and sulfuric acid)on the immersion were researched.Under the optimum conditions:50 °C,80 min,sulfuric acid and sodium chloride 150 g./L and 18 g/L,the leaching rate of gold reached 93.16%.And after extraction and reduction,the purity of the finally obtained gold is 98.54%,and the recovery rate of gold is 88.61% in the whole process.Finally,integrating the above research,this paper proposed an efficient and promising process for recycling waste TFCRs with the core of mechanical separation-vacuum pyrolysis-selective leaching.The economic assessment was taken in detail calculation of cost and benefit,and the results showed that our recycling process was positive.The combination process has realized the sustainable target with 3R,which is suitable for further industrialization and application.What’s more,the necessary pretreatment is provided for the next recovery,providing reliable information for further industrial applications and contributing to more depth and refinement development of e-waste resource recovery. |
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