GB622495A - Improvements relating to the treatment of laundry and the like trade effluents - Google Patents

Abstract

A process for the treatment of laundry and other soap-containing trade effluents comprises adding washed precipitated aluminium or iron hydroxide, hydrated oxide or oxide, dried or in the form of a slurry, either alone or admixed with an alkaline-earth carbonate to effect the precipitation of the dissolved soap and/or to effect the coagulation or de-emulsification of the suspended matter, screening or filtering or both, and conducting the whole operation under such conditions as to conserve heat. The aluminium or iron hydroxide, hydrated oxide, or oxide is prepared by precipitation from a solution of an aluminium or iron salt with an alkali metal, alkaline earth, magnesium or ammonium oxide, hydroxide, carbonate or bicarbonate. The resulting precipitate is washed with water to remove the alkali, alkaline earth, magnesium or ammonium ions, and used as a wet or dried and powdered concentrate, or made into a slurry. Addition to the laundry effluent first causes precipitation of the dissolved soap, coagulation of this precipitate and of suspended matter resulting when excess is added. Alkaline earth compounds such as magnesium oxide, hydroxide, or carbonates may be added before or with the aluminium or iron hydroxide. The reaction vessels are heat-insulated so that only a small drop in temperature ensues during the process. According to one example a hard paste of aluminium hydroxide is prepared from solutions of aluminium sulphate and sodium carbonate followed by filtration and washing. From the paste a slurry is formed with water, and 100 parts of the slurry containing one part aluminium oxide is added to 10,000 parts laundry effluent, avoiding excessive agitation, the resulting liquor being filtered through stainess steel cloth. In another example 50 parts chalk slurry containing a half part of calcium carbonate are added to 70,000 parts laundry effluent, and 50 parts aluminium oxide slurry containing a half part aluminium oxide are added, followed by the step of filtration. In a third example magnesium basic carbonate is added to a slurry of ferric hydroxide made from ferric chloride and a lime suspension, the resulting slurry containing equal parts of ferric hydroxide and magnesium basic carbonate. 100 parts slurry containing a half part of each constituent are added to 10,000 parts laundry effluent, followed by filtration. In all the examples the temperature drop is from about 65 DEG C. to about 50 DEG C. The filter residue may be treated with sulphuric acid to yield insoluble fatty acids for re-use as a soap stock, and soluble aluminium sulphate from which the hydroxide may be prepared for re-use.