Influence of impurities in zincate zinc plating solution and treatment methods

Zincate< Strong class="keylink">The impurities in the galvanizing solution are divided into two categories: inorganic and organic. The common inorganic impurities are copper and lead, the organic ones are mainly the decomposition products of organic additives in the bath, and the pre-treatment is not clean and brings people-some grease and other dirt. Too much organic impurities will cause the coating to fog and bloom, and in severe cases, it will bring brittleness to the coating. Organic impurities treatment is more convenient, as long as activated carbon treatment is carried out when necessary according to the situation, or treatment is carried out on a regular basis. Let’s talk about the hazards of copper and lead impurities and how to deal with them.

The metal impurities in the zincate zinc plating solution should not be treated with sodium sulfide, because the complexation of sodium hydroxide to zinc ions is relatively weak. If the concentration of sodium sulfide added is too high or the amount added is too much, it will often The zinc ions combine to form milky white zinc sulfide and precipitate; the zinc sulfide particles are relatively coarse, and the deposition on the cathode will cause the coating to produce burrs. Because its concentration is difficult to control, and if it is not properly added, it will cause disadvantages, so sodium sulfide is generally not used as a treatment agent for heavy metal impurities. Also because the zincate bath contains no strong complexing agent sodium cyanide, the zincate zinc plating solution should be more sensitive to impurities than the cyanide zinc plating solution. The fact is exactly the same, we can also see from the passivation color of the parts after galvanizing, if the purity of the zincate zinc plating solution is slightly lower, it is difficult to obtain a blue-white appearance using the white passivation process. According to our experiment, the copper ion impurity in the bath should not be greater than 15mg/L. A small amount of copper impurities will affect the color tone of the passivation film, slightly higher-some make the passivation film foggy, and more often, it will turn black after the nitric acid emits light. Copper impurities can be treated with electrolysis at low current density, or with zinc powder or alkaline zinc plating impurity remover, etc., but prevention should be the first priority.

Lead impurities are mainly caused by poor quality zinc plates. Lead is more harmful than copper, especially barrel plating. High lead impurities will cause the zinc coating to not deposit. If this kind of plating solution is tested with the Hull tank, it is possible that the plating is normal, which often makes the technicians who deal with the fault on the spot like falling into a cloud of fog, because–I can’t get the idea. There are many lead impurities. Except that the barrel plating layer is not deposited, the plating layer will appear yellowish brown after the light nitric acid is released. After passivation in the low chromium passivation solution, the film layer will show a yellow interference color. Get a beautiful blue and white hue. The lead content should be controlled below 2mg/L. Lead can also be treated with electrolysis at low current density, or with alkaline zinc plating impurity remover, or CK-778. The effect of these two impurity removers is better than zinc powder. They can also reduce hexavalent chromium and can adsorb organic impurities. When these two kinds of impurity remover are used for treatment, they must be sprinkled and stirred vigorously. At this time, some of the impurity remover adsorbs some organic impurities and will float on the surface of the plating solution, which can be scooped out with a spoon. The precipitated and suspended impurity remover together with impurities are removed by filtration.