U.S. Borax, Inc.

Honghi N Tran

Robert B McBroom

Charles M Bair

A method is provided for the use of borates in the recausticization of alkali-containing liquors such as those produced in the chemical and semi-chemical pulping of wood and in the oxidation and bleaching of wood pulp. Sodium hydroxide is regenerated from sodium carbonate-containing smelts in such pulp processes by autocausticization through the addition of limited amounts of borate. Autocausticization may be carried out at boron to carbonate molar ratios below 2:1 and at sodium to boron molar ratios exceeding 3:1, resulting in high reaction efficiency. Partial autocausticization using borate may also be combined with conventional lime recausticization for the regeneration of sodium hydroxide from sodium carbonate-containing smelts.

Method for regenerating sodium hydroxide by partial autocausticizing sodium carbonate containing smelt by reaction with borate

A method is provided for improving causticizing efficiency in the conventional lime recausticization portion of an alkaline pulping process. Such processes are commonly used in the pulping and bleaching of wood and non-wood cellulose fiber materials. The method of this invention comprises reacting an aqueous solution of sodium carbonate with lime to produce sodium hydroxide (causticization) in the presence of borate in order to improve the causticization reaction efficiency. Borate is added in an amount sufficient to provide a boron to sodium (B/Na) molar ratio in the range of between about 0.001:1 and 0.4:1, and preferably in the range of between about 0.01:1 and 0.3:1, which results in an increased causticization efficiency of up to 8% over the reaction efficiency obtained in the absence of borate.

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Toronto, Canada

Honghi N Tran