Using acid to remove the oxide scale and rust on the steel surface is called acid washing or acid pickling. It is a way to clean the metal surface. This process is usually carried out together with a pre-passivating treatment. Here are many acids for pickling: sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid, and mixed acid ect. However, only H2So4 and HCl are the most popular. Acid washing normally is a pre-treatment or intermediate treatment for electroplating, enamel, rolling and other processes.
Regarding this acid washing wastewater can not be directly discharged, because it can cause great pollution. First, it will bring serious drainage corrosion. Second, it will affect aquatic organisms. Moreover, it will cause soil calcification and impede crops growth. Finally, if flow into drinking water, it can cause diseases, such as gastroenteritis.
Most of the pickling wastewater comes from steel plants or electroplating plants. The pH value is generally below 1.5 (free acid 0.5-2%). So it is strongly acidic. In China, such waste water is disposed by neutralization method. The neutralizing agents popularly used are lime, because of cheap cost and easy to operate. The process basically do not adopts biological methods, only physical method is enough. After neutralization, it will be dewated by pp chamber filter press. If want to buy China filter press, please contact SINO FILTRATION.