A process is described for removing iron and/or transition metal impurities from aqueous aluminium salt solutions, in which the aluminium salt solutions are admixed with at least one alkyldithiocarbamate of the formula; IMAGE in which R and R', which can be identical or different, are each a hydrogen atom or an alkyl group, in particular a methyl, ethyl, propyl or isopropyl group, with R and R' not simultaneously being hydrogen atoms, and M is an alkali metal, in particular a sodium or potassium, or ammonium ion, and/or at least one alkylenebisdithiocarbamate of the formula: IMAGE in which: M is a sodium, potassium or ammonium ion and n is an integer from 2 to 4. This process advantageously starts with aqueous aluminium salt solutions, in particular aqueous aluminium sulfate, aluminium chloride and/or aluminium nitrate solutions, which have been obtained in the treatment of aluminium-containing clays such as bauxite, halloysite, kaolinite, alunite, montmorillonite or alum shale (slate) with a corresponding inorganic acid. The precipitate formed in the treatment of the aluminium salt solutions with the additive can be hydrolysed with a sodium, potassium or ammonium hydroxide solution to recover the respective alkyldithiocarbamate of the formula (I) and/or alkylenebisdithiocarbamate of the formula (II).
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