Method for producing coagulant aluminium salts

A method for producing a coagulant aluminium salt, the method comprising

• obtaining raw material comprising at least one aluminium oxide compound,
• mixing the raw material comprising the at least one aluminium oxide compound with a process acid or a base to form a reaction mixture,
• heating the reaction mixture to a reaction temperature of at least 100° C. at a reaction pressure,
• maintaining the reaction mixture at the reaction temperature and reaction pressure for a reaction time, and allowing the at least one aluminium oxide compound to react with the process acid or the base, and
• cooling the reaction mixture,
• wherein the at least one aluminium oxide compound is selected from a group consisting of amorphous aluminium oxide, γ-aluminium oxide, η-aluminium oxide, χ-aluminium oxide, and any of their mixtures and wherein the reaction pressure is at least 2 bar(g).