Caustic waste liquor

Several units are used for sulfite-paper-mill waste-liquor disposal. At least six units are used for oil-refinery wastes, whicdi sometimes include a mixture of liquid sludges, emulsions, and caustic waste... 

The process starting from lignin has faced serious problems, such as reduced availability and environmental impact. The availability is reduced because the new process for making paper paste yields less liquor. As a result, it is likely that the larger companies will not reinvest in new factories to process liquors to meet demand. The process s environmental impact is also problematic because over 160 t of caustic waste are produced for every ton of vanillin manufactured. 

Step 8. The waste liquor from the reactor centrifuge flows to a waste liquor neutralizer, where the HCl is neutralized with a caustic soda (sodium hydroxide) solution ... 

The exit stream from the neutralizer joins with the effluent liquor from the product centrifuge. Most of the combined stream is fed to a waste treatment facility, but a portion of it is fed to the NaOH makeup tank (a batch stirred tank) to prepare more caustic feed solution for the neutralizer. Enough NaOH(s) is added to the makeup tank to bring the solution concentration back up to 10 wr% NaOH. Each batch prepared in this manner contains enough solution to supply the waste liquor neutralizer for eight hours of operation (one shift). When the NaOH pellets have completely dissolved and a batch is ready, a valve in the tank exit line is opened and the batch is fed by gra it> to the NaOH feed drum, from which solution is pumped continuously to the waste liquor neutralizer,... 

Amongst the applications of dialysis in industry the most outstanding one over a long period of time has been the recovery of caustic soda in the pulp industry. This recovery amounts to a great saving in caustic soda and it greatly reduces the disposal problem of the waste liquor. This industrial application is an example wherein the two prerequisites listed above are eminently met to make dialysis the chosen method for attaining the purposeful recovery of caustic soda. 

Abbreviations GC/FID, gas chromatography/flame ionization detection GC/MS, gas chromato-graphy/mass spectrometry GC/PID, gas chromatography/photoionization detection Includes groundwater, sludges, caustic and acid liquors, waste solvents, oily wastes, mousses, tars, fibrous wastes, polymeric emulsions, filter cakes, spent carbons, spent catalysts, soils, and sediments... 

Porous carbon and graphite are used in filtration of hydrogen fluoride streams, caustic solutions, and molten sodium cyanide in diffusion of chlorine into molten aluminum to produce aluminum chloride and in aeration of waste sulfite liquors from pulp and paper manufacture and sewage streams. 

Historically, a classic example of an evaporation process is the production of table salt. Maple syrup has traditionally been produced by evaporation of sap. Concentration of black liquor from pulp and paper processing constitutes a large-volume present application. Evaporators are also employed in such disparate uses as desalination of seawater, nuclear fuel reprocessing, radioactive waste treatment,preparation of boiler feed waters, and production of sodium hydroxide. They are used to concentrate stillage waste in fermentation processes, waste brines, inorganic salts in fertilizer production, and rinse liquids used in metal finishing, as well as in the production of sugar, vitamin C, caustic soda, dyes, and juice concentrates, and for solvent recovery in pharmaceutical processes. 

Emission problems in a causticization operation arise chiefly in the area of dust control of the exit gases from the lime kiln since the water circuit is virtually self-contained. Effective containment is obtained by the use of scrubbers, which achieve some 99% mass removal efficiency from the exhaust gases. Spent scrubber liquor may be returned to the causticization circuit for recycle. Using spent scrubber liquor, either for the slaking of lime or to prepare fresh sodium carbonate solutions for causticization, avoids creating a water emission problem from this aqueous waste stream. It also improves the raw material balance of the process. 

The caustic liquor produced in a membrane cell is weaker than that from a mercury cell. Typical concentrations are 30-35% NaOH and 28-32% KOH. The net production of caustic solution goes to evaporation and final processing. The caustic solution also recycles around the catholyte side of the cells. This allows control of both temperature and concentration. A cooler removes the waste heat generated in the cells, and water addition keeps the catholyte concentration at the desired level. 

Chlorine scrubber waste solutions are a special case here. The controlled reaction of chlorine and caustic soda produces commercial bleach solutions. A loss of strict control of the reaction conditions allows the hypochlorite produced by the primary reaction to degrade (Section 9.1.10.3A). In an emergency scrubber, total capture of chlorine that is released unpredictably and at highly variable rates is a more urgent goal than is the preservation of the hypochlorite. The liquor may then become a waste product. It should be considered a hypochlorite waste and treated as in Section 16.5.2.6. 

Various formulations are provided under this heading by Terry (1893), the common factor being the likely creation of complex oiganic residues. The three recipes provided are as follows (1) Fused caustic potash is digested in alcohol, and the liquor filtered and heated till a brown powder is thrown down, which is filtered and washed with acidulated water (2) Waste cotton, peat, or brown coal, heated with an alkali (3) Farinaceous matters carbonised by mineral acids. ... 

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