ANTIACID PROTECTION

1. –  Leaching Phase.
2. –  Solvent Extraction Phase.
3. –  Electrowinning Phase.

Given that the concentration of sulfuric acid in these three phases is different, the design requirements of the acid-protection systems are also different. On the other hand, when these plants are located in the desert, the surfaces exposed to weather suffer from thermal gradients up to 30°C between day and night, so the coefficient of expansion of the coating plays a key role in its service life. In the case of leaching, the structures exposed to corrosion are mainly conveyor belts and specific equipment used in this process. These elements are exposed to weather, so even though the concentration of sulfuric acid in the leaching solution may be low (1%), because of the evaporation of water due to the sun and wind, the concentration of acid solution settled on the surfaces increases significantly and becomes highly aggressive. The paint scheme design should consider this condition. In the case of SX Plants, the coatings should be resistant both to sulfuric acid and to the solvents used in the process. In this process, exposed steel surfaces correspond to lightweight equipment and structures. Most of the surfaces are pools, dikes, floors, corridors and piping, all made of concrete. In the case of EW bay, the concentration of sulfuric acid in the electrolytic solution exceeds 20%. During the process, moisture evaporates, dragging the sulfuric acid and copper sulphate, which are settled on the metal and concrete surfaces, causing severe and rapid deterioration of the structures and coatings that protect them. In this case, the coatings must have great chemical resistance and impermeability to the aggressive environment. The design of the coatings, standardization and quality of the products that compose them, work plan during the application, quality control and quality assurance of the application and the finished product, are fundamental variables of the studies, controls and planning that must be executed for the success and service life of antacid protection systems in these plants. In short, the characteristics of the coatings that should be considered for the protection of metal and concrete structures of the different sectors of the wet area, require high chemical resistance and a coefficient of expansion as close as possible to the substrates they protect.

In keeping with the above, the technical solution for each case should be thoroughly studied since a poor technical analysis can generate sub-sized solutions, with an excessive increase on the cost/benefit ratio. Projects executed according to appropriate studies, reduced the coating costs for steel structures by more than 30%. The evaluation after 2 years of operation, shows no corrosion at all and an excellent state of the coatings. In contrast, projects carried out without these previous studies, show premature and severe corrosion problems after 1-year operation.