A process and apparatus for regeneration of acid and metal from spent acid liquors includes the steps of, optionally, concentrating (110) the liquor to a concentrated liquor or solid, pyrohydrolysing (114) to regenerate the acid and form metal oxide pellets, and reducing the oxide to metal in a two stage reduction reactor (116, 118) using a partially combusted fuel as reducing agent. Also disclosed is a two-stage reduction process and reactor for production of direct reduced iron (DRI) from iron oxide ores or wastes, including a first stage (416) in which the oxide feed is contacted with a fuel and a sub-stoichiometric amount of an oxygen source to produce a lower oxidation state oxide, and a second stage (418) in which the lower oxidation stage oxide is contacted with off-gases from the first stage to produce iron metal.