| With the rapidly development of technology,the electronic products,the output of electronic products are rapidly changing,and the production of electronic products increased year by year.Therefore,the waste(electronic waste)generated by electrical and electronic equipment has become the fastest-growing waste stream.Waste printed circuit boards(WPCBs)are the main carrier of precious metals and harmful metals in electronic waste,and the metals in WPCBs were very complex.If not handled properly,it will not only pollute the environment,damage human health,but also cause huge waste of resources.And the grade of metal in WPCBs was significantly higher than natural ore,so recycle meats in WPCBs has high potential economic value.Compared with other recovery methods,hydrometallurgical recovery method has higher accuracy,selectivity and predictability.However,for traditional hydrometallurgical process,inorganic acids,such as sulfuric acid,hydrochloric acid and nitric acid,are widely used in present process,which are easy to corrosion equipment and damage the health of operators.In addition,the release of Cl2,SO3,NOx and acidic waste water in the leaching process will polluted the environment inevitably,so it is urgent researcher to develop an environmentally friendly and efficient leaching process.It is a new enviormental leaching process the using green and cheap organic acids as leaching agents to leaching metals from WPCBs.Aiming at the shortcomings of organic acids,such as weak acidity and slow reaction rate,it is proposed to strengthen the mass transfer effect of solid-liquid interface by ultrasonic,accelerate the leaching process.Firstly,the acids(citric acid,acetic acid and hydrochloric acid)were used to leaching copper from WPCBs,and the leaching rate of copper of different acids and various factors were explored.The results show that citric acid and acetic acid could leach copper effectively,and the maximum leaching rates were 92.17 % and 91.82 %,respectively.The changes of material composition were analyzed by XRD,and it was found that the peak value of copper was significantly reduced,and no other peaks were produced,which proved that copper was effectively leached and the chemical reaction products were dissolved in water.The structure of the leaching residue was further characterized by zoom stereomicroscope combined with SEM.It was found that the copper not involved in the reaction was mainly in the form of copper-glass fiber-epoxy resin.Compared with hydrochloric acid,the leaching time of citric acid and acetic acid was longer,for 100 min and 120 min,respectively.The leaching kinetics of citric acid and acetic acid conformed to Avrami equation,and the leaching process was controlled by chemical reaction diffusion.The apparent activation energies were 44.36 k J/mol and75.19 k J/mol,respectively.Based on the understanding of various factors on citric acid and acetic acid leaching of copper,the influence of ultrasonic on the leaching process was explored.The experimental results show that ultrasonic can significantly improve the leaching rate of copper,and the leaching time is shortened by 40 min and 60 min respectively,and the maximum leaching rate of citric acid is increased to 97.09 %.By fitting the leaching kinetic model and calculating the apparent activation energy,it was found that the apparent activation energies of citric acid and acetic acid were 20.49 k J/mol and15.99 k J/mol,respectively.Compared with the conventional leaching,the reaction activation energies were reduced by 23.87 k J/mol and 59.20 k J/mol,respectively.The leaching process of copper was expanded by chemical reaction.The leaching process of copper changed from chemical reaction diffusion control to solid film diffusion control.In order to further understand the effect of ultrasonic on materials,using particle size analyzer to analyze the effect of ultrasonic on materials,and the particles of WPCBs were further broken by ultrasonic.Compared with conventional leaching result,the average particle size of leaching residue produced by ultrasonic leaching is reduced,the leaching residues of citric acid and acetic acid are reduced by 387.08 μm and 300.71μm,respectively.Scanning electron microscope(SEM)was used to observe the surface of glass fiber.It was found that the surface of glass fiber was smooth and the adhesion was reduced compared with conventional leaching.It was proved that ultrasonic cavitation formed micro jet continuously impacting particles,promoted solid-liquid mass transfer effect and promoted chemical reaction efficiency.This article has 72 figure,22 tables,and 111 references. |
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