GB1430602A - Processes for the treatment of waste liquids - Google Patents

Abstract

1430602 Wet air oxidation NIPPON STEEL CORP 23 July 1973 [22 July 1972 (2) 22 Nov 1972] 35071/73 Heading C1C [Also in Divisions C4-C5] Removal of H 2 S, NH 3 and, where present, HCN, from gases is effected by successively contacting the gas with (i) (optional) an aqueous solution or dispersion containing sulphur and/or polysulphides at pH > 7 to absorb HCN; (ii) an aqueous solution containing a redox catalyst at pH # 7 to absorb H 2 S; and (iii) an aqueous solution containing sulphate ions to absorb NH 3 and precipitate ammonium sulphate. Before recycling, the spent liquor from (ii) is regenerated by contact with an oxygen-containing gas (e.g. air) and its pH restored by drawing off a part thereof and replacing it with water, with addition of alkali if necessary. The drawn-off liquid is optionally filtered to remove sulphur (which may be fed to stage (i)), and is fed, optionally together with liquor similarly drawn off from absorbing solution circulating in stage (i), to a wet air oxidation stage (vide infra) from the effluent of which ammonium or calcium sulphate may be recovered; alternatively the effluent is fed to stage (iii). The gas may be coke oven gas, petroleum decomposition gas, petroleum purification gas, coal decomposition gas, natural gas, or gas from organic waste treatment. The redox catalyst may be iron oxide, manganese oxide, picric acid or a derivative thereof, or a quinone, naphthoquinone or anthraquinone derivative. Wet air oxidation of the above effluent, which contains one or more of sulphur, sulphites, thiosulphates, thiocyanates and polysulphides, is effected by contacting it with an oxygencontaining gas (e.g. air or oxygen, preferably in excess) at a temperature above 150‹ C. and at a pressure (e.g. 4À7-120 atm.) greater than the saturated vapour pressure of water at the temperature used. The effluent may be initially diluted with water and pre-heated by heatexchange with the oxidized liquor. Alkali (e.g. lime, quicklime, CaCO 3 , NaOH, Na 2 CO 3 , KOH, K 2 CO 3 , NH 3 , NH 4 OH) may be added before or after the oxidation so that the pH of the oxidized sulphate-containing liquor is above 7.