Abstract: In the invention pickling process, steel and nickel or chromium alloys are pickled with an acidic pickling solution employing an oxidant, particularly hydrogen peroxide, and in which liquor is recirculated through inlets comprising a nozzle feeding liquor into a diffuser such that liquor is withdrawn from the bath and the volume of liquor flowing through the diffuser is a multiple of flow through the nozzle. Steel or the alloys are pickled with an acidic solution containing iron and free hydrogen peroxide at a concentration of up to 0.1 gpl. The process can operate effectively at a free fluoride concentration of from 20 to 30 gpl and a sulphuric acid concentration of from 80 to 110 gpl. The lifetime of the bath before it needs to be replaced can be lengthened by the process compared with using an air agitation system.