In metal processing, pickling baths containing sulfuric acid used to clean steel surfaces are assumed that are exhausted when the bath becomes saturated with ferrous sulfate at around 80-90 g/L. At saturation, the bath is regarded as ineffective and is discarded as waste material. To our knowledge, however, there is no experimental evidence showing that saturation determines the exhaustion of the bath and stops the pickling reaction. We therefore tested whether ferrous sulfate saturation stops the pickling reaction by adding different amounts of ferrous sulfate to a 20% sulfuric acid pickling bath and analyzing the pickling rate of A36 steel. We found that pickling rates were similar in saturated baths containing ferrous sulfate concentrations as high as 300 g/L. We have thus confirmed that the pickling rate depends primarily on the proton concentration of the bath. (C) 2014 Elsevier Ltd. All rights reserved.