Electrochemical Enhanced Recovery of Precious Metals from Electronic Waste
In order to dissolve base metals such as Cu and Sn, chemical dissolution methods consume significant quantities of acids which add to process costs. An alternate method of dissolving metals involves using a chemical mediator to attack the base metals. The mediator can be turned over electrochemically to limit the amount of chemicals added and the metals dissolved depend on the oxidizer generated in the process. While the use of a strong oxidizer will dissolve all metals from the material , the approach taken in this work uses a weaker oxidizer that attacks the base metals (Cu, Sn, Zn, Ni) in the non ferromagnetic fraction of mobile electronic devices (steel fragments are magnetically separated prior to processing). This approach has been taken as the remaining small concentrations of precious metals can be extracted efficiently with minimum chemical consumption.
In this work, the recovery of base metals has been performed using the Fe+3/+2 mediator couple as the oxidant. Work has progressed from pure metals to recovery from milled recycled phone materials. Figure 1 shows the outlet composition of an experiment where a Fe+3 solution was continuously fed to an extraction reactor containing milled phone material while collecting the outflow. The extraction order of metals follows the galvanic series where Sn is observed initially and Cu appears only after most of the Sn is removed. This suggests that selective recovery could be achieved. The process has been developed using an electrochemical cell, operating in series with an extraction reactor containing phone material. The oxidant generated at the anode is flowed through the reactor and returned to the cathode side of the cell for recovery at the cathode. The process has achieved over 90% recovery of metals.
Figure 1. Fraction of metal extracted from milled cell phone material through a continuous feeding of 0.2 M Fe2(SO4)3 in 1 M H2SO4.
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