The Study On Wet-efficient Extracting Silver From Components Of Waste Mobile Phones

Electronic waste is known as“urban mine”because it has a large content of rare and precious metals.For purposes of reducing the excessive exploitation of mines and protecting the environment,e-waste should be recycled properly.Nowadays,increasingly new technological innovation and rapidly short product life cycles have led to a significant increase in waste mobile phones.In this study,thiosulfate leaching method was used for the recovery of silver from the electronic components of waste mobile phones and some reagents were added to enhance silver leaching rate.Additionally,zinc deoxidization method was adopted to recycle the silver ion from the silver leaching solution.Based on these approaches,the experimental investigation of this study leads to main conclusions that can be summarized as follows:(1)The factors were obtained in terms of the method of orthogonal test on leaching silver from electronic components.The experimental results showed that the degree of these element factors(from big to small)was:reaction time>ammonia concentration>sodium thiosulfate concentration>copper sulfate concentration.The optimal leaching experimental conditions were,respectively,0.2 mol/L sodium thiosulfate,0.2 mol/L ammonia,0.01mol/L copper sulfate when the temperature was 313 K under the conditions of the liquid-solid ratio 200 for 24 h,and the leaching rate of silver was about 80%.Additionally,the gold leaching by using this method was also investigated.It was found that the gold leaching rate was only 15%,relatively lower than that of silver when the concentration of sodium thiosulfate was 0.3mol/L,and the leaching time was 24 h.(2)When sodium citrate with the concentration of 0.05 mol/L was added into the thiosulfate solutions,silver leaching rate was approximately 94%in the best leaching condition.Compared with that of none of sodium citrate,the silver leaching rate increased about 14%,the consumption of thiosulfate dropped the tendency for 63 mmol/L.It indicated that the sodium citrate can promote silver leaching,and reduce the consumption of sodium thiosulfate.(3)In order to improve the efficiency of leaching silver,30mmol/L L-arginine,50mmol/L L-lysine,and 50 mmol/L L-histidine were added.The silver leaching efficiency of94%,95%and 96%can be respectively achieved.The amount of thiosulfate that remained in the solution rised from 43 mmol/L to 140 mmol/L in the leaching process to some extent,thus the consumption of thiosulfate significantly decreased.Arginine,lysine,histidine were all alkaline amino acid,all of those can be complexed with silver ion in the thiosulfate leaching solution.These results showed that the addition of amino acid not only improved the leaching rate of silver,but also reduced the consumption of thiosulfate.Furthermore,the safety and non-toxic could provide some technical support for the environmentally-friendly leaching silver.(4)Based on the above research,silver ion could be deoxidized to silver element by using zinc in this part.The whole course of the reaction was controlled by the addition amount of zinc because it was the significant influencing factor.When Prob>F value was0.0065,which was far less than 0.0500,the reaction time had little impact on the reduction rate of silver.Based on the influences of zinc concentration,temperature,reaction time and their interactions on the reduction rate of silver,it can be concluded that the simulation curve model was Y=76.65+25.51A+14.91B+34.09C+8.00AB-7.28 AC+5.40 BC-17.80 A~2+4.39 B~2+38.00 C~2,where Y was the silver reduction rate,A was the amount of zinc,B was the reaction temperature and C was the reaction time.This model can be effectively used to predict the reduction effect of silver according to the three factors under different conditions,and it provided a theoretical basis for the actual reduction conditions of silver from electronic waste.