Sodium chloride removal in pulp mill systems
AssigneeErco Envirotech Ltd.
InventorsJerome A. Lukes, Robert P. Schroeder
Life of this patent
Estimating the term…
Abstract
Smelts produced in Kraft mill and soda mill spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the removal of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided in the case of the soda mill, or first is separated from the sodium sulphide in the case of the Kraft mill. Thereafter, the solid mixture is leached to remove the sodium carbonate and sodium sulphate while leaving the sodium chloride in a substantially pure form, the resulting leach liquor being refrigerated to deposit sodium carbonate and sodium sulphate. The mother liquor, after removal of the deposited salts is recycled to the solid mixture leaching step.
Claims24
In a pulp mill process which comprises digesting cellulosic fibrous material with a pulping liquor containing sodium hydroxide and sodium sulphide as the pulping chemicals, separating pulped material from spent pulping liquor, introducing sodium chloride to said spent pulping liquor, forming a smelt containing sodium sulphide, sodium carbonate, sodium chloride and sodium sulphate from said spent pulping liquor, fractionating said smelt to form an aqueous sodium sulphide solution and a solid mixture of sodium carbonate, sodium sulphate and sodium chloride substantially free from sodium sulphide, and recycling said aqueous sodium sulphide solution to said digestion step to provide at least part of said sodium sulphide in said pulping liquor, the improvement which comprises leaching said solid mixture with an aqueous medium to dissolve substantially completely said sodium carbonate and sodium sulphate therefrom thereby to form an aqueous sodium carbonate and sodium sulphate solution and leave substantially pure solid sodium chloride, refrigerating said aqueous sodium carbonate and sodium sulphate solution to deposit a solid mass of sodium carbonate and sodium sulphate substantially free from sodium chloride, separating said deposited solid mass from the mother liquor, forming an aqueous solution of said separated mass, converting at least a substantial proportion of the sodium carbonate in the aqueous solution of said mass to sodium hydroxide, recycling the resulting sodium hydroxide solution to said digestion step to provide at least part of said sodium hydroxide in said pulping liquor, and recycling said mother liquor to provide part of said aqueous medium leaching said solid mixture.
In a pulp mill process which comprises digesting cellulosic fibrous material with a pulping liquor containing sodium hydroxide as the pulping chemical, separating pulped material from spent pulping liquor, introducing sodium chloride to said spent pulping liquor and forming a smelt containing sodium carbonate, sodium chloride and sodium sulphate from said spent pulping liquor, the improvement which comprises leaching said smelt with an aqueous medium to dissolve substantially completely said sodium carbonate and sodium sulphate therefrom thereby to form an aqueous sodium carbonate and sodium sulphate solution and leave substantially pure solid sodium chloride, refrigerating said aqueous sodium carbonate and sodium sulphate solution to deposit a solid mass of sodium carbonate and sodium sulphate substantially free from sodium chloride, separating said deposited solid mass from the mother liquor, forming an aqueous solution of said separated mass, converting at least a substantial proportion of the sodium carbonate in the aqueous solution of said mass to sodium hydroxide, recycling the resulting sodium hydroxide solution to said digestion step to provide at least part of said sodium hydroxide in said pulping liquor, and recycling said mother liquor to provide part of said aqueous medium leaching said solid mixture.
Dependencies are inferred from the claim text.