Heavy rust and scale should be removed form
metal surface before entering into subsequent surface
treatment processes. The iron rust removing process is
by immersing the metal in mineral acids and the
process is called pickling [12]. Sulfuric acid is the
most widely used one, because its lower price and can
be used at higher temperatures up to approximately
65 °C [13,14]. Hydrochloric acid is somewhat more
vigorous in action than sulfuric and can be used at
room temperature; however, the resulting fumes may
be a problem [14]. Recently, many steel pickling
facilities have changed from sulfuric acid to
hydrochloric one. Despite the advantage of lower cost
of sulfuric acid, hydrochloric acid pickling offers
faster and cleaner pickling, lower acid consumption,
greater acid utilization, and lesser quantities of wasted
pickle liquor. In addition, the product quality is better
than that by using sulfuric acid as a pickling liquor.
When the rust (mostly iron oxides) dissolves in
hydrochloric acid, ferrous chloride is formed
according to the following reactions