Electrochemical Dissolution Of Poorly Soluble Precious Metal Rhodium Law And Process Conditions Studied

At present, with the development of the automobile industry and fine chemicals,the demand of rhodium-based compounds increased rapidly. Rhodium is available inthe form of metal powders in the world market, and dissolution of rhodium powdersis the first step as well as the crucial step in preparing rhodium-based compounds,particularly rhodium chloride, for rhodium is known to be very difficult to bedissolved by conventional chemicals. Some techniques including calcination withbarium peroxide, chlorination at high temperatures and/or under great pressures, havebeen developed and are being used in dissolving rhodium powder andrhodium-containing wastes, but are often compromised by low efficiency andintroduction of undesired substances. It is therefore necessary to develop new,efficient and environmentally acceptable processes for dissolving the metal.The electrochemical dissolution is quite different from calcination andchlorination. Despite the low dissolution rates, it can be used to produce somechemical compounds in one step and without contamination of other metal ions suchas sodium and potassium. In the context, the electrochemical dissolution of rhodiumboth by direct currents and by alternating currents were investigated in present work,aiming at look for better dissolving conditions, such as temperature, current density,HCl concentration, time, oxydol amount.It is shown that the electrochemical dissolution rate of rhodium is largelydetermined by electrolytic conditions such as temperature, current density, HClconcentration, time, oxydol amount, and the optimum conditions for thiselectrochemical dissolution of rhodium to prepare rhodium chloride are as follows:(1) temperature of the electrolyte is50-60℃,(2)current density is3-5A/cm2,(3) theratio of the apparent area of rhodium to the volume of HCl is1to300.