Redução do consumo de ácido crômico na galvanização de peças metálicas

Abstract

The galvanizing process is usually used in finishing parts aiming at greater durability through the application of a metallic layer by electrodeposition. Door handles, padlocks and assembly components are galvanized with decorative chrome, which gives the pieces a more elegant finish. Chromium is a compound that when found in its trivalent oxidation form is beneficial to health, however, in hexavalent oxidation, commonly used in electroplating, it is toxic and can cause problems for human health and the environment. The drag from the chromium bath to the rinse water causes an increase in the concentration of hexavalent chromium in the following stages, directly impacting the water treatment plant and the consumption of inputs to replace the amount dragged in a given period. Aiming at lower chromium drag and reduction of the mist formed by the gases in the electrodeposition, a new surfactant was applied, which in smaller quantities has a greater effect. By measuring the surface tension with the addition of the surfactant, it was possible to determine the critical micellar concentration point (CMC) of the surfactant and how the chromium bath behaves with this change. Having verified that the surfactant acts by reducing surface tension without interfering with the concentrations of chromic acid present in the bath, a comparison was made of the concentration of chromium in the rinse water in the periods, before, during and after the change. To ensure the accuracy of the comparison, the production of chrome parts in these same periods was considered and how this influenced the concentration of chromium. In the year 2022, the number of pieces produced was 1.960,7% higher than in the year 2020 for the same concentration of 0,1 mg/L of chromic acid in water, while the cost of producing each piece, in the same period, reduced by R$0,58 to R$0,02. Similarly, there was a reduction in input consumption of 97,8% chromic acid and 98,24% surfactant, indicating a potential cost reduction of up to R$1.737.317,46 for the production of chrome parts, in addition to concentration stability of chromium in water.