Electrochemical Method Is The Determination Of The Gelatin Concentration In The Copper Electrolyte

It's well-known that to add some additives in the electrolyte of copper is necessary, and the additive, especially the glue, is very important in copper electrorefining. One of the additives, its name is glue, it can increase the cathode overpotential, make cathode crystal more compact and it can promote the formation of new crystal. But the amount of the additives in the electrolyte must be accurate; otherwise, some serious affection may be bring by the inaccurate additives. Especially in high current density, the quantity of cathodic surface will get worse if the amount of the additives is controlled inaccurately.The concentration of the active glue in copper electrolyte is hard to determine, the reasons are: 1.the complicated molecular formula of glue; 2. molecular weight is uncertain; 3. decomposed at high temperature; 4. concentration is so low (ppm class). Some copper refineries in China carried out a chemic method to determine the glue, the principle of this method is to determine the total nitrogen concentration. Unfortunately, there is a fatal disadvantage that the glue decomposed in high temperature but nitrogen not. The concentration of the glue can only be judged by observe the surface of cathode in Chinese copper refinery, this method is immature because it is difficult to determine the accurate concentration of glue by naked eye, and misjudgment occurs frequently.Some foreign copper refineries carried out an advanced method to determine the concentration of the glue. It is an on-line system, it measures the cathodic overpotential intermittently and records the value of overpotential chronically, after it records a period of time, the system get an appropriate overpotential and adjust the concentration of glue automatically base on the overpotential value. The principal of this system is simple, but we all know, the overpotential is a complex parameter that many factors can affect it, not only the concentration of glue, but also the temperature, the Cu²⁺ concentration and so on.Combined the difficulties in China and other local and foreign documents, this text did some theoretic research: the glue concentration-overpotential relationship is dissimilar in different temperature, current density, copper concentration. The author also do some research with glue when the electrolyte contained other additives, and the conclusion is that thiourea can increase the function of glue, but the glue concentration-overpotential relationship became obscure when thiourea exist in the electrolyte. In order to find an obvious relationship of the glue concentration-overpotential, some hydrogen peroxide can be added into the electrolye to remove the thiourea. At last, the author get two samples of the real electrolyte, and the concentration of glue in the two samples have been determined: the concentrations are 1.41 mg/L and 0.72 mg/L in the condition t=30℃and D_k=50A/m²; and the concentrations are 0.37 mg/L and 0.40 mg/L in the condition t=65℃and D_k=300A/m².