摘要
Traditionally,Ag-containing solid wastes are leached by nitric acid in order to recycle the noble metal.However,the huge amounts of emission of toxic nitrogen oxides demand the development of a new method for silver recycling.Recently,considering the Ce(Ⅳ)solution could be regenerated with electrolyzation method,our group invented a novel environmentally friendly process by using Ce(Ⅳ)as the oxidant to dissolve silver from the spent Ag/ɑ-Al_2O_3 catalysts without NO_x emission.To find out the optimal parameters,in this work,the leaching reaction was thoroughly investigated with respect to the temperature,oxidant and HNO_3 concentrations,stirring speed,and time.The optimized leaching reaction gave the leaching silver rate 99.8% in 1 h.The kinetic plots suggested a shrinking core model with the internal diffusion-controlled process and the activation energy of 38.83 k J·mol^(-1).The order in which the experimental conditions influence the reaction was determined through orthogonal analysis:temperature N oxidant concentration N HNO_3 concentration N stirring speed.
Traditionally,Ag-containing solid wastes are leached by nitric acid in order to recycle the noble metal.However,the huge amounts of emission of toxic nitrogen oxides demand the development of a new method for silver recycling.Recently,considering the Ce（Ⅳ）solution could be regenerated with electrolyzation method,our group invented a novel environmentally friendly process by using Ce（Ⅳ）as the oxidant to dissolve silver from the spent Ag/ɑ-Al2O3 catalysts without NOx emission.To find out the optimal parameters,in this work,the leaching reaction was thoroughly investigated with respect to the temperature,oxidant and HNO3 concentrations,stirring speed,and time.The optimized leaching reaction gave the leaching silver rate 99.8% in 1 h.The kinetic plots suggested a shrinking core model with the internal diffusion-controlled process and the activation energy of 38.83 k J·mol-1.The order in which the experimental conditions influence the reaction was determined through orthogonal analysis：temperature N oxidant concentration N HNO3 concentration N stirring speed.
基金
Supported by the Key Research Program of Frontier Sciences of CAS(QYZDJ-SSWJSC021)
the Science and Technology Cooperation for Yunnan Provinces and CAS(2016IB002)
Science and Technology Service Network Initiative of CAS(KFJ-SW-STS-148)
National Natural Science Foundation of China(21506233,51402303,21606241,51374191)
