Electrolytic treatment--removal of metal impurities in plating solution-Huizhou Huigao Automation Equipment Co., LTD.,| Fully automatic electroplating equipment | Environmental protection equipment | Electrophoresis equipmentoxidation equipment

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Electrolytic treatment--removal of metal impurities in plating solution

release time:

2021-09-15

Electrolytic treatment is a commonly used method for removing impurities in the electroplating industry. Electrolytic treatment is also an electroplating process, but it is not for the purpose of obtaining a good electroplating layer, but for removing impurities (or adjusting the composition of the plating solution). The difference is that the parts are not hung on the cathode, but an electrolytic plate (also called a false cathode) made by hanging to remove impurities. When energized, impurities are deposited, entrapped or reduced to relatively harmless substances on the cathode electrolytic plate. In a few cases, the removal of impurities by electrolysis is also carried out on the anode, so that some impurities that can be oxidized, when energized, reach the anode and oxidize into gas to escape or become relatively harmless substances.

Electrolytic treatment--removal of metal impurities in plating solution

First, the choice of electrolysis conditions

The purpose of electrolysis here is to remove impurities in the plating solution, but the removal of impurities by electrolysis is often accompanied by discharge deposition of main metal ions in the solution. In order to improve the removal rate of impurities and slow down the deposition rate of the main metal ions in the solution, it is necessary to pay attention to the operating conditions of the electrolytic treatment.

① Current density: During electrolytic treatment, it is better to control the current density. In principle, it should be based on the current density range where impurities have adverse effects during electroplating. That is to say, in the electroplating process, if the influence of impurities is reflected in the low current density area, the electrolytic treatment should be controlled at a low current density. If the influence of impurities is reflected in the high current density area, the high current density should be selected. Carry out electrolysis; if the impurity affects both the high current density area and the low current density area, you can first use the high current density electrolysis treatment for a period of time, and then switch to the low current density electrolysis treatment until the plating solution returns to normal. In general, for impurities that can be removed by low current density electrolysis, low current density electrolysis is generally used in order to reduce the deposition of the main discharge metal ions in the plating solution. In fact, in electroplating production, the influence of most impurities is reflected in the low current density area, so the current density of electrolytic treatment is usually controlled between 0.1A/dm2 and 0.5A/dm2.

② Temperature and pH value: The selection of temperature and pH value during electrolytic treatment, in principle, should also be based on the temperature and pH range that have a great influence on impurities during electroplating. For example, the copper impurities and NO3- impurities in the nickel plating solution have a greater impact when the pH is low. Therefore, when the copper impurities and NO3- impurities in the nickel plating solution are electrolytically removed, a low pH should be used for electrolysis. Under such conditions The rate of removal of impurities is faster. Some impurities will be decomposed into gases during the electrolysis process (such as NO3- is reduced to nitrogen oxides or ammonia on the cathode, Cl- is oxidized to Cl2 on the anode, etc., at this time, high-temperature electrolysis should be used to make the formed during the electrolysis process. The volatilization of the gas escapes (the solubility of the gas in the solution, which generally decreases with increasing temperature), thereby preventing it from dissolving in water and recontaminating the bath.

According to a general rule, as the temperature of the plating solution increases, the rate of electrolytic removal of impurities also increases, so when the heating has no effect on the main components of the plating solution, the electrolytic treatment should be carried out under heating. But what temperature to control is better, it is best to determine through a small test.

③ Stirring: Since the electrolytic treatment relies on the reaction of impurities on the surface of the cathode (or anode) to be removed, conditions should be created so that the impurities have sufficient opportunities to contact the surface of the electrode. Stirring can accelerate the movement of impurities and increase the chance of contact with the electrode, so in order to improve the treatment effect, the plating solution should be stirred during electrolysis.

2. Requirements for electrolytic treatment

① First of all, it is necessary to find out whether the harmful impurities come from the electrolysis process: electrolytic treatment can remove some impurities, but sometimes impurities are also generated. For example, harmful impurities come from impure anodes, which are still used during electrolysis, so as the electrolysis process proceeds, impurities will accumulate more and more; if impurities come from the decomposition of certain compounds on the electrodes, then electrolysis This kind of decomposition products will gradually increase. Such electrolytic treatment will not only fail to purify the plating solution, but will continue to aggravate the pollution of the plating solution. Therefore, before the electrolytic treatment, necessary inspections should be carried out to prevent the generation of harmful impurities during the treatment.

The cathode (false cathode) area for electrolysis should be as large as possible: the removal of impurities by electrolysis is mostly carried out on the surface of the cathode, so increasing the cathode area can improve the efficiency of removing impurities. Electrolytic removal of different impurities or the same impurity in the plating solution requires that the cathode for electrolysis be made into a concave and convex surface (such as corrugated shape), which can improve the effect of electrolytic treatment. However, the recesses on the cathode should not be too deep to prevent the current density from being too small to prevent impurities from being deposited or reduced in these locations.

③ During the electrolysis process, the cathode should be brushed regularly: since the electrolysis treatment time is generally long, loose deposits may be generated on the cathode during the long-term electrolysis process, and its fall off will re-contaminate the plating solution, so After electrolysis for a period of time, the cathode should be taken out and brushed, and the loose or bad deposits on the cathode should be brushed off before continuing electrolysis.

④ Before electrolytic treatment, it is best to do a small test to estimate the effect and time of electrolytic treatment: some impurities are difficult to remove with electrolytic treatment. If electrolytic treatment is used blindly, it may take a long time to restore the plating solution to normal. .