Abstract: A method of regenerating an etching waste fluid, includes the steps of dissolving HCl gas in an etching waste fluid at a temperature falling within a range of 20.degree. C. to 50.degree. C. and crystallizing NiCl.sub.2 and FeCl.sub.2 crystals, the etching waste fluid containing NiCl.sub.2, FeCl.sub.3, and FeCl.sub.2 and being obtained by etching Ni or an Ni alloy with an etching solution consisting of an aqueous solution containing FeCl.sub.3, distilling a mother liquor at the atmospheric pressure after crystallization and separation thereof to reduce the HCl concentration in the mother liquor, and distilling, at a reduced pressure, a concentrate obtained upon distillation at the atmospheric pressure to further reduce the HCl concentration, thereby obtaining an aqueous solution containing FeCl.sub.

Abstract: The present invention provides a process for recovering a tungsten compound from a waste liquor containing a high-boiling organic compound and the tungsten compound, which process comprises the steps of spray-burning said waste liquor at an air ratio of 1.05 or higher under conditions of a temperature and a residence time which lie within the region of a pentagon defined by points A, B, C, D, and E in FIG. 1; quenching the combustion product by immediately bringing it into direct contact with water; and recovering the tungsten compound.

Abstract: An improved process for the recovery of ammonia and sulphur dioxide from a by-product mixture containing an ammonium salt of sulphuric acid obtained as a by-product in the preparation of .epsilon.-caprolactam or cyclohexanone oxime. The by-product mixture is reacted, in finely divided form and at a temperature of from 700.degree. to 950.degree. C., with gases obtained from the combustion of a fuel in a controlled amount of oxygen, and ammonia and sulphur dioxide are thereafter separated from the resulting reaction mixture. The amount of oxygen is controlled to be less than the theoretical additional amount that would be required to convert the nitrogen, sulphur, hydrogen and carbon contained in the by-product mixture and fuel into, respectively, N.sub.2, SO.sub.2, H.sub.2 O and CO.sub.2.

Abstract: A process for treating a hydrogen sulfide-containing gas in a closed loop system wherein said gas is passed through and absorbed by an alkaline aqueous absorbent containing an alkali carbonate and an oxidation catalyst. The solution containing the dissolved hydrogen sulfide is oxidized with an oxygen-containing gas to convert the absorbed hydrogen sulfide into elementary sulfur and sulfur salt compounds. After separation of the elementary sulfur from the solution, the solution is re-circulated for use as alkaline absorbent. A part of the re-circulated solution is diverted and subjected to mixed-combustion with an auxiliary fuel in a combustion furnace at an air ratio lower than 0.9 and at a temperature of 700.degree.C to 1100.degree.C to thermally decompose the sulfur compounds into hydrogen sulfide and an alkali carbonate.