SILVER ELECTROWINNING IN NITRIC MEDIUM - ELIMINATION OF CONTAMINATINGIONS

Silver electrorefining is classically performed in nitrate medium. In such a medium, it is difficult to separate mercury from silver. In thi s note, we have studied the possibility of mercury separation, using t he current-potential curves, at analytical scale as well as at semi-pr actical conditions. We have observed that a concentration of 0.002 M i n mercury in a 0.74 M silver nitrate electrolyte is still too high to obtain a purification effect. In another paper, we have proposed a met hod to achieve the mercury/silver separation based on the mercury sele ctivity of complexing agents such as EGTA, Mercury ions give anionic s pecies which are separated by anion exchange. If such a method of puri fication is coupled to the electrolysis, the electrolyte contains, by recycling, small amount of this complexing agent. We concluded that it is possible to obtain at the cathoce silver of good purity.