Patent ID: 8394529

Claim:
A method for preparing a redox flow cell battery electrolyte, comprising: mixing a raw material comprising a transition metal and at least one ionic impurity, in at least one first aqueous acid to form a mixture comprising ions of the transition metal and at least one ionic impurity, wherein the transition metal is selected from the group consisting of chromium, iron, and a combination thereof; subjecting the mixture to at least one ammonium salt, wherein at least one ionic impurity precipitates out of the mixture; removing at least a portion of the precipitates from the mixture, to form a partially purified mixture of ions of the transition metal; treating the partially purified mixture with ammonia, wherein at least a portion of ions of the transition metal in the partially purified mixture precipitate in the form of oxide and/or hydroxide salts; removing at least a portion of the precipitated oxide and/or hydroxide salts from the partially purified mixture; and at least partially solubilizing the oxide and/or hydroxide salts by mixing the ions of the transition metal, in the form of oxide and/or hydroxide salts, in at least one second aqueous acid to form the electrolyte.