| The human environment and resources face a challenge agin with the rapid growth of the number of waste mobile phones.If they are not properly disposed of,it will cause the problem of environmental pollution and waste of resources.The content of gold,silver and palladium is also high in the waste phone mobile components except for copper,iron,nickel and other metals.The recovery of metal in the waste mobile phone components is an important process for the recycling of waste mobile phones.The content of tin,lead and zinc in the waste cell phone is also high.At present,there are not many technologies for recovering them.As tin,lead and zinc are amphoteric metal,the study uses sodium nitrate as oxidant to extract and recycle them in alkaline medium.When the traditional heating methods are used to assist alkaline leaching of tin,lead and zinc in mobile phone components,it cost long time and its leaching rate is low.In order to solve this problem and improve the leaching effect,microwave heating is used to replace traditional heating.Besides,we also studied the activation of samples by mechanical activation to improve the activity of samples.Before the leaching experiment,the metal types and metal content in mobile components were tested and analyzed.The results showed that the contents of tin,lead and zinc in mobile components are 6.761%,0.251% and 1.371%,respectively.From this analysis,we can see that mobile phone components are rich in tin resources and zinc resources,and contain a certain amount of heavy metal lead.Therefore,it is important to dispose the mobile components with a resourceful and harmless way.The leaching rate of tin,lead and zinc can be effectively improved by using microwave heating instead of traditional heating.On the basis of the experimental study,the optimum leaching process is that the concentration of sodium hydroxide is20%,the concentration of sodium nitrate is 6%,the temperature is 90,the time is90 min,the ratio of liquid to solid is 60,the microwave power is 500 W,and under these conditions,the leaching rates of tin,lead and zinc are 83.19%,69.69% and88.21%,respectively.And the leaching rates of copper,iron and nickel in mobile phone components are 0.48%,4.13% and 0 respectively.It can be seen from this that the alkaline leaching method can effectively achieve the separation of tin,lead andzinc from other components of mobile phone.The kinetic study on the leaching process shows that the apparent activation energy and apparent reaction order of metal tin,lead and zinc are lower than that of conventional heating when microwave is used as heating condition.Taking tin as an example,the apparent activation energy and apparent reaction order are30.14kJ/mol and 0.59.However,in traditional heating,the apparent activation energy and apparent reaction order of tin are 50.47kJ/mol and 1.Therefore,using microwave as heating condition is favorable for leaching reaction.Mechanical activation treatment can effectively improve the leaching rate of Sn,Pb and Zn.When the activation time is 60 min,the activation speed is 450 rpm,and the ratio of ball to material is 20g/g,the leaching ratio of tin,lead and zinc are 92.02%,72.94%and81.82%,respectively.The mechanical force of the sample increases with the increase of ball milling speed or the ratio of the ball to the sample,and more of the tin in the sample is oxidized to SnO2.This caused the tin is difficult to dissolve and the leaching rate decreases.The alkaline leaching process is applied in this study,which is highly selective,and the progress is helps to extract metals step by step.The waste gas will not be produced in the process of treatment.The alkaline leaching solution can also be recycled for leaching reaction after recovering metals,and will not cause secondary pollution. |
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