Recovering metal values from marine manganese nodules

Claim 1

A method for refining manganese bearing marine nodules, comprising: (a) leaching the nodules with an aqueous solution of nitrous and nitric acids having a pH below about 2.5 to selectively dissolve manganese, copper, nickel, and cobalt coupled with the least dissolution of iron; (b) separating insoluble iron oxide and gangue from the leach solution at a pH of less than 2.5; (c) adding to the solution a quantity of manganous hydroxide at least equal to the stoichiometric value of the metals other than manganese present in the solution to selectively precipitate copper, nickel, and cobalt; (d) removing precipitated copper, nickel, and cobalt hydroxides from the manganese nitrate containing solution.

Claim 2

A method for refining manganese bearing marine nodules, comprising: (a) leaching the nodules with an aqueous solution of nitrous and nitric acids having a pH below about 2.5 to selectively dissolve manganese, copper, nickel, and cobalt coupled with the least dissolution of iron; (b) separating insoluble iron oxide and gangue from the leach solution at a pH of less than 2.5; (c) adding to the solution a quantity of manganous hydroxide at least equal to the stoichiometric value of the metals other than manganese present in the solution to selectively precipitate copper, nickel, and cobalt; (d) removing precipitated copper, nickel, and cobalt hydroxides from the manganese nitrate containing solution.

Claim 9

A method of processing marine nodules to selectively recover manganese values, the nodules comprising primarily oxides of Mn and Fe with lesser proportions of compounds of Cu, Ni, Co, alkali metals and alkaline earth metals, which method comprises the steps of: (a) washing the nodules with water until substantially all soluble chloride salts have been removed; (b) leaching the nodules at a temperature below about 80° C. with an aqueous solution of nitrous and nitric acids having a pH of 1.0-2.0 under an equilibrium partial pressure of a combination of nitric oxide and water vapor less than atmospheric pressure, wherein said nodules contain a stoichiometric excess of manganese dioxide equivalent in relation to the nitrous acid content of the aqueous solution, to selectively dissolve Mn, Cu, Ni, and Co while retaining substantially all of the iron oxide in the gangue; (c) filtering the resulting slurry containing Mn, Cu, Ni, Co, alkali metal and alkaline earth metal nitrates at a pH of less than 2.5 to remove insoluble iron oxide and gangue; (d) adding Mn(OH) 2 to the filtrate in a quantity at least equal to the stoichiometric value of the Cu, Ni and Co metals present in the solution to selectively precipitate said metals as hydroxides; (e) adding to the filtrate a quantity of H 2 S in any proportion up to the Mn(OH) 2 equivalent present to precipitate additional metal traces as sulfides; (f) filtering the solution to remove precipitated metals and separate the manganese nitrate solution.

Claim 10

A method of processing marine nodules to selectively recover manganese values, the nodules comprising primarily oxides of Mn and Fe with lesser proportions of compounds of Cu, Ni, Co, alkali metals and alkaline earth metals, which method comprises the steps of: (a) washing the nodules with water until substantially all soluble chloride salts have been removed; (b) leaching the nodules at a temperature below about 80° C. with an aqueous solution of nitrous and nitric acids having a pH of 1.0-2.0 under an equilibrium partial pressure of a combination of nitric oxide and water vapor less than atmospheric pressure, wherein said nodules contain a stoichiometric excess of manganese dioxide equivalent in relation to the nitrous acid content of the aqueous solution, to selectively dissolve Mn, Cu, Ni, and Co while retaining substantially all of the iron oxide in the gangue; (c) filtering the resulting slurry containing Mn, Cu, Ni, Co, alkali metal and alkaline earth metal nitrates at a pH of less than 2.5 to remove insoluble iron oxide and gangue; (d) adding Mn(OH) 2 to the filtrate in a quantity at least equal to the stoichiometric value of the Cu, Ni and Co metals present in the solution to selectively precipitate said metals as hydroxides; (e) adding to the filtrate a quantity of H 2 S in any proportion up to the Mn(OH) 2 equivalent present to precipitate additional metal traces as sulfides; (f) filtering the solution to remove precipitated metals and separate the manganese nitrate solution.