The Pickling of steel
The Pickling of steel
One of the most important applications of hydrochloric acid is in the pickling of steel, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling, galvanizing, and other techniques.Technical quality HCl at typically 18% concentration is the most commonly used pickling agent for the pickling of carbon steel grades.
Fe2O3 + Fe + 6 HCl → 3 FeCl2 + 3 H2O
The spent acid has long been re-used as iron(II) chloride (also known as ferrous chloride) solutions, but high heavy-metal levels in the pickling liquor have decreased this practice.
The steel pickling industry has developed hydrochloric acidregeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula:
4 FeCl2 + 4 H2O + O2 → 8 HCl+ 2 Fe2O3
By recuperation of the spent acid, a closed acid loop is established.The iron(III) oxide by-product of the regeneration process is valuable, used in a variety of secondary industries.
Fe2O3 + Fe + 6 HCl → 3 FeCl2 + 3 H2O
The spent acid has long been re-used as iron(II) chloride (also known as ferrous chloride) solutions, but high heavy-metal levels in the pickling liquor have decreased this practice.
The steel pickling industry has developed hydrochloric acidregeneration processes, such as the spray roaster or the fluidized bed HCl regeneration process, which allow the recovery of HCl from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula:
4 FeCl2 + 4 H2O + O2 → 8 HCl+ 2 Fe2O3
By recuperation of the spent acid, a closed acid loop is established.The iron(III) oxide by-product of the regeneration process is valuable, used in a variety of secondary industries.