The key reaction in a regeneration plant is the decomposition of the iron chloride solution within the spray roasting reactor. This reaction requires the presence of water vapor and oxygen at temperatures between approximately 600 and 1600 degrees F.

The following basic reactions take place:

2FeCl₂ + 2H₂O + ½O₂ ---- Fe₂O₃ + 4HCl
2FeCl₃ + 3H₂O ------------ Fe₂O₃ + 6HCl

Spent pickle liquor is fed from the tank farm to the regeneration plant, which consists essentially of an acid preconcentrator (also called a venturi recuperator) (1), a spray roasting reactor (2), an absorption column (3), and a tailgas scrubber (4).

Spent acid from the tank farm is preconcentrated in the venturi recuperator (1) utilizing hot gases from the spray roasting reactor.

The spray roasting reactor (2) consists of a cylindrical vessel lined with refractory ceramic material with several burners arranged tangentially around the perimter. Preconcentrated waste acid is injected through spray nozzles into the upper part of the reactor (2). The burners, which are oil or gas fired, supply hot gases to the inside of the reactor (2), thus producing vortex flow. Droplets produced by the nozzles are entrained by the vortex flow and intimately mixed with the reactor atmosphere. As the droplets descend,  water and hydrochloric acid evaporate so that an agglomeration of chloride crystal form on the crust.

When the vapor escapes, the crust is frequently perforated or broken. The chloride particles formed in this manner produce a metal oxide and hydrochloric acid gas with the original agglomerated remaining largely intact.

The oxide is continuously withdrawn from the cone shaped bottom of the roaster (2) by a rotary feeder. It is then pneumatically conveyed to a storage bin.

Reactor exhaust gases are removed from the reactor, and depending on the type of plant, passed through one or two cyclones for dust precipitation. In the downstream preconcentrator (1), the exhaust gases are cooled to approximately 200°F in direct contact with the solution.

Hydrochloric acid gas is subsequently removed from the cooled exhaust gases in an adiabatic absorption column, and leaves the column in the form of hydrochloric acid at a concentration of approximately 18%. The roaster gases at this point contain only very small amounts of hydrochloric acid in addition to water vapor. Inert gases such as nitrogen, oxygen, and carbon dioxide are then removed from the column by fan. Water is then fed into the fan and a tail gas scrubber (4) to remove most of the traces of hydrochloric acid from the roaster gases. Together with rinse water, this water is used to absorb hydrochloric acid in the absorber (3). A slight negative pressure is maintained in the roaster reactor as well as in all other downstream parts of the plant by the exhaust fan so that vapor, or oxide dust are prevented from escaping into the atmosphere (5).