Sulfate spent liquor

Chemical recovery ia sodium-based sulfite pulpiag is more complicated, and a large number of processes have been proposed. The most common process iavolves liquor iaciaeration under reduciag conditions to give a smelt, which is dissolved to produce a kraft-type green liquor. Sulfide is stripped from the liquor as H2S after the pH is lowered by CO2. The H2S is oxidized to sulfur ia a separate stream by reaction with SO2, and the sulfur is subsequendy burned to reform SO2. Alternatively, ia a pyrolysis process such as SCA-Bidemd, the H2S gas is burned direcdy to SO2. A rather novel approach is the Sonoco process, ia which alumina is added to the spent liquors which are then burned ia a kiln to form sodium aluminate. In anther method, used particulady ia neutral sulfite semichemical processes, fluidized-bed combustion is employed to give a mixture of sodium carbonate and sodium sulfate, which can be sold to kraft mills as makeup chemical. 

After conversion to the use of sodium-based chemicals, spent liquor could be incinerated, and sulfur dioxide, sodium sulfate, carbonate, or sulfide could be recovered. These compounds could be sold for use at nearby kraft mills or for other industrial uses. 

Calcium Lignosulfonate occurs as a brown, amorphous polymer. It is obtained from the spent sulfite and sulfate pulping liquor of wood or from the sulfate (kraft) pulping process. It may contain up to 30% reducing sugars. It is soluble in water, but not in any of the common organic solvents. The pH of a 1 100 aqueous solution is between approximately 3 and 11. 

Raghava Rao et al. [89] selectively removed neutral salts contained in spent chromium tanning solutions to achieve a more efficient technique for recycling the unused chromium and process water. The electrodialysis unit contained Neosepta CL-25T and ACH-45T membranes. An application of 13-30 V to a 5 dm solution over a period of 5 - 6 h produced currents between 2 and 4 A 90% of the sodium chloride and 50% of the sodium sulfate were selectively removed with minimal transport of Cr(III) species across the membranes. Addition of EDTA to the spent liquor as well as periodic reversal of electrode polarities eliminated membrane fouling. 

Wood is the raw material of the naval stores industry (77). Naval stores, so named because of their importance to the wooden ships of past centuries, consist of rosin (diterpene resin acids), turpentine (monoterpene hydrocarbons), and associated chemicals derived from pine (see Terpenoids). These were obtained by wounding the tree to yield pine gum, but the high labor costs have substantially reduced this production in the United States. Another source of rosin and turpentine is through extraction of old pine stumps, but this is a nonrenewable resource and this industry is in decline. The most important source of naval stores is spent sulfate pulping liquors from kraft pulping of pine. In 1995, U.S. production of rosin from all sources was estimated at under 300,000 metric tons and of turpentine at 70,000 metric tons. Distillation of tall oil provides, in addition to rosin, neady 128,000 metric tons of tail oil fatty acids annually (78). 

H.C. Bramer and J. Coull, Electrolytic regeneration of spent pickling solution, Ind. Eng. Chem., 1955, 47, 67-70 C. Homer, A.G. Winger and G.W. Bodamer, R. Kunin, Electrolytic treatment of waste sulfate pickle liquor using anion exchange membranes, Ind. Eng. Chem., 1955, 47, 1121 D.J. Lewis and F.L. Tye, Treatment of spent pickle liquors by electrodialysis, J. Appl. Chem., 1959, 9, 279-292. 

Cooking liquor - 539, 693 Pulp stocks - 539 Spent liquor - 539, 540 Paper, alkaline pulping Cooking liquor 540, 693 Pulp stocks - 540 Spent liquor - 540, 541 Paper alum (see Aluminum sulfate)... 

Paper and pulp mill condensate - 189, 206 Paper and pulp mill gas, noncondensable 203 Paper, bleach solutions - 541, 693, 694, 724 Paper, groundwood pulp stocks - 541 Paper machine - 204 Paper mill liquor - 204, 206, 539, 724 Paper, neutral sulfite Cooking liquor - 541 Pulp stocks - 542 Spent liquor - 542 Paper, paperboard waste 542 Paper, parchmentizing - 542 Paper pulp, bleached - 694 Paper pulp slurry 694 Paper, sizing solution - 543 Paper stock 694 Paper, white water Acid - 543 Groundwood - 543 Neutral sulfite - 543 Newsprint - 543 Paperboard 544 Soda - 544 Sulfate - 544 Peracetic acid - 30 Parachloride 230... 

The primary cooking chemicals in the kraft process are sodium hydroxide and sodium sulfide. The sodium sulfate which is added to the spent liquor is reduced to sodium sulfide in the recovery furnace. Sodium carbonate is also present but does not participate in the pulping process it is converted to sodium hydroxide during the recausticizing process. 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

Nickel sulfate can be produced from either pure or impure sources. The pure source involves the reaction of pure nickel or nickel oxide powder (combined or separately) with sulfuric acid to produce nickel sulfate that is filtered and crystallized to produce a solid product. The impure raw material may be spent industrial liquor that contains a high percentage of nickel sulfate. The impurities in the liquor are precipitated by sequential treatment with oxidizers lime and sulfides can later be filtered out. The treated liquor, which is a pure solution of nickel sulfate, can be packaged in a drum or further crystallized and dried to produce solid nickel sulfate. Nickel sulfate is used mainly in the metal plating industries. Other uses include dyeing and printing of fabrics and production of patina, an alloy of zinc and brass. 

Sulfite and sulfate ions were precipitated from the spent birch liquor (Fig. 1) with barium hydroxide. Monosaccharides and other low molar mass non-electrolytes and weak electrolytes were separated quantitatively from the lignosulfonates by means of ion exclusion chromatography (5). 

Precipitation also can be induced by additives, a process generally called salting out because salts with ions common to those whose precipitation is desired are often used for this purpose. For instance, ammonium chloride is recovered from spent Solvay liquors by addition of sodium chloride and the solubility of BaCl2 can be reduced from 32% to 0.1% by addition of 32% of CaCl2. Other kinds of precipitants also are used, for instance, alcohol to precipitate aluminum sulfate from aqueous solutions. 

Kraft processes are applicable to nearly all species of wood, and effective means of recovering spent cooking chemicals for recycle in the process have been developed. Some sodium and sulfur losses do occur and are replenished in the cooking-liquor system by adding sodium sulfate at the recovery boiler, where it is converted to sodium carbonate and sulfide. Ill order lo maintain a proper sulfur-lo-sodium ratio in the recovered chemicals, other chemicals, such as sodium carbonate, sodium sulfite, and sulfur, are sometimes used for chemical makeup. 

Gierer J, Lindeberg O (1980) Reactions of lignin during sulfate pulping Part XIX Isolation and identification of new dimers from a spent sulfate liquor Acta Chem Scand B 34... 

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