A method for the processing of potassium containing materials comprises: (i) Separation of a potassium containing mineral from gangue minerals; (ii) Acid leaching whereby substantially all potassium, iron, aluminium and magnesium is solubilised and mixed potassium/iron double salt formed; (iii) Selectively crystallising the mixed potassium/iron double salt formed in the leach step (ii); (iv) Second separation to separate the mixed potassium/iron double salt formed in step (iii); (v) Thermal decomposition to produce an iron oxide, a potassium salt and one or more phosphates; (vi) Leaching the product of the thermal decomposition; (vii) Third separation to separate the iron oxide and phosphate from the potassium salt; (viii) Recovering the potassium salt by crystallisation; (ix) Separating the iron oxide and phosphate of step (vii) by leaching and subsequent solid liquid separation; and (x) Precipitating phosphate from liquor produced in step (ix) through the addition of a base.

A method of processing a non-virgin sulfuric acid solution for the preparation of aluminum sulfate comprises the steps of combining a sulfuric acid solution having less than about 90% sulfuric acid with a water solution to form a mixed solution of no less than about 10% sulfuric acid. An alumina-containing compound such as aluminum hydroxide or aluminum bauxite is then added to the mixed solution to form aluminum sulfate.

A method of processing a non-virgin sulfuric acid solution for the preparation of aluminum sulfate comprises the steps of combining a sulfuric acid solution having less than about 90% sulfuric acid with a water solution to form a mixed solution of no less than about 10% sulfuric acid. An alumina-containing compound such as aluminum hydroxide or aluminum bauxite is then added to the mixed solution to form aluminum sulfate.

A method for the processing of potassium containing materials comprises: (i) Separation of a potassium containing mineral from gangue minerals; (ii) Acid leaching whereby substantially all potassium, iron, aluminum and magnesium is solubilized and mixed potassium/iron double salt formed; (iii) Selectively crystallizing the mixed potassium/iron double salt formed in the leach step (ii); (iv) Second separation to separate the mixed potassium/iron double salt formed in step (iii); (v) Thermal decomposition to produce an iron oxide, a potassium salt and one or more phosphates; (vi) Leaching the product of the thermal decomposition; (vii) Third separation to separate the iron oxide and phosphate from the potassium salt; (viii) Recovering the potassium salt by crystallization; (ix) Separating the iron oxide and phosphate of step (vii) by leaching and subsequent solid liquid separation; and (x) Precipitating phosphate from liquor produced in step (ix) through the addition of a base.

Methods of removing one or more oxyanions from an aqueous fluid can comprise increasing the pH of an aqueous fluid containing one or more oxyanions and contacting the aqueous fluid with aluminum metal.