Abstract: Soda values from the crystallizer mother liquor purge in the process of making sodium carbonate from trona are recovered by (1) mixing the purge with treating agent of magnesium oxide, aluminum oxide, bauxite, certain fine particle size calcined trona, insoluble impurities obtained in the trona-soda ash process, or mixtures thereof, (2) evaporating the resulting mixture to dryness and calcining it to insolubilize soluble silicates and to reduce contamination with carbonaceous impurities, and (3) leaching the calcined mixture with water or aqueous sodium carbonate solution.

Abstract: Sodium chloride is removed from Kraft mill smelts by fractionating the smelt to separate sodium carbonate and sodium sulphate in solid form from sodium sulphide and sodium chloride which usually is contaminated with residual quantities of sodium carbonate and sodium sulphate and is contained in an aqueous solution thereof. Sodium chloride subsequently is separated from the aqueous solution. Various fractionation procedures are described and various procedures for the removal of the sodium chloride in substantially pure form also are described.

Abstract: Exhaust gases from a high pressure, high temperature fluidized bed reactor are fed through a turbo expander, in order to drive said turbo expander which is connected to a device such as a generator, adapted to accomplish useful work. Preferably, the exhaust gases pass through a particulate removal means prior to passing through the turbo expander.

Abstract: A new chemical recovery process and apparatus for a polysulfide pulping system is described wherein sulfur is recovered from the weak black liquor and is returned to the process, along with makeup sulfur, to reconstitute the polysulfide solution.After the polysulfide digestion, the spent liquor is contacted with ferric oxide Fe.sub.2 O.sub.3 whereby ferrous sulfide, FeS, is formed. After separation of the ferrous sulfide from the remaining liquid, the ferrous sulfide is oxidized to form elemental sulfur, and ferric oxide. After the melting of the sulfur and the separating of the products, the sulfur can be returned to the Sulfur Dissolving Tank wherein, along with makeup sulfur as required, the white liquor from the causticizing plant can be treated to form the polysulfide liquor for digestion. The ferric oxide can be reused for contacting the black liquor to form ferrous sulfide. The resulting smelt of reduced sulfidity from the recovery furnace can be reprocessed to form the white liquor.

Abstract: Smelts produced in spent pulping liquor recovery operations and containing sodium chloride are treated to remove sodium chloride therefrom in pure form while the loss of usable components is avoided. A solid mixture of sodium chloride, sodium carbonate and sodium sulphate is provided as such in a soda mill, or first is separated from sodium sulphide, by fractionating the smelt where sodium sulphide is present, as in the Kraft mill. The solid mixture is leached at a high temperature to remove all the sodium chloride values therefrom, along with part of the sodium carbonate and sodium sulphate. Pure sodium chloride is deposited by cooling the leach liquor and the mother liquor is recycled to the leaching step.

Abstract: In the recovery and regeneration of spent pulping chemicals from the production of cellulosic fibrous material pulp there is provided a white liquor containing dissolved quantities of sodium chloride and unregenerated pulping chemicals. The white liquor is concentrated by evaporation to deposit therefrom sodium chloride and unregenerated pulping chemicals, unregenerated pulping chemicals substantially free from sodium chloride are recovered from the deposited materials, and sodium chloride is separated and recovered from the deposited materials. The deposition of sodium chloride and unregenerated pulping chemicals is usually carried out in two stages, with unregenerated pulping chemicals substantially free from sodium chloride being deposited in the first stage. The sodium chloride then is deposited in the second stage, possibly in admixture with unregenerated pulping chemicals, in which event substantially pure sodium chloride is separated from the deposited mixture.

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.

Abstract: The liquid phase coking of waste kraft pulping liquors can be effected with a shorter residence time in the coking means at lower temperature, and lower pressure by reducing the pH of such liquors by at least one pH unit before coking. Products are lower in malodorous organic sulfur components than those produced at a higher pH.The lowering of the pH is achieved by adding sulfur dioxide to the liquor either as free SO.sub.2 or as an aqueous solution of SO.sub.2.