Method of separating sodium hydroxide from white liquor or polys

Details Method of separating sodium hydroxide from white liquor or polys Method of separating sodium hydroxide from white liquor or polys

1997-02-25

1998-12-01

Chin, Peter

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210649, 162 3011, 162 42, 162 50, C02F 144, C01D 732

Patent

active

058433163

ABSTRACT:
The present invention relates to a method of processing white liquor obtained from the causticization stage of a pulp mill. According to the method, the white liquor, which principally contains sodium hydroxide (6) and sodium sulfide, is oxidized into polysulfide liquor (3), whereby the sodium sulfide is oxidized most advantageously with the help of a catalyst and an oxidizer such as air substantially into sodium polysulfide (7) and sodium thiosulfate. The method according to the invention is characterized in that the sodium hydroxide (6) contained in the white liquor is separated from the white liquor prior to the oxidizing step or from the polysulfide liquor (3) after the oxidizing step either entirely or partly by means of a diffusion dialysis process (4). The invention is further characterized in that the sodium hydroxide (6) separated from the white liquor is returned to the chemical circulation of the pulp mill.

REFERENCES:
patent: 4024229 (1977-05-01), Smith et al.
patent: 5061343 (1991-10-01), Azarniouch et al.
patent: 5326433 (1994-07-01), Ryham et al.
patent: 5382322 (1995-01-01), Magnotta et al.
patent: 5510035 (1996-04-01), Toronen et al.
Chemical Abstract, vol. 104, 1986, Abstract No. 52978.
Chemical Abstract, vol. 116, 1992, Abstract No. 135712.

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