Abstract: The present invention lies in a method of improving a Langelier index and pH of city water wherein undissolved matter (calcium carbonate and slaked lime covered with calcium carbonate) slurry produced in a slaked lime dissolving vessel is mixed and reacted with carbonic acid-containing water in a mixing and reacting vessel to make a calcium hydrogen carbonate aqueous solution so as to continuously add to water in a water-receiving vessel together with a slaked lime aqueous solution, with which a utilization percentage of undissolved matter which has hitherto had a low utilization percentage is increased, and the Langelier index can be improved.

Abstract: A method of producing an aqueous solution of slaked lime is disclosed the steps of: introducing water into a slaked lime-dissolving apparatus comprising a dissolving tank, a water supply piping connected to a lower part of the tank, a stirring blade disposed within the tank in its bottom part, an effluent piping connected to an upper part of the tank for discharging aqueous slaked lime solution, and a fluidized slaked lime layer height-control device disposed within the tank above the stirring blade, subsequently introducing a predetermined amount of slaked lime into the tank, feeding water, with low-speed stirring, to the tank from the water supply piping in such a rate that the water in the cylindrical or rectangular upper part of the tank ascends at a rate of from 0.25 to 1.2 mm/sec, and taking out an aqueous solution of slaked lime from the tank through the effluent piping.

Abstract: The Langelier index and pH of city drinking water are improved by mixing and reacting a slurry of calcium carbonate and slaked lime covered with calcium carbonate produced in a slaked lime dissolving vessel with carbonic acid-containing water in a mixing and reacting vessel to make a calcium hydrogen carbonate aqueous solution which in turn is continuously added to water in a water-receiving vessel together with the aqueous solution of slaked lime. As a result, unused undissolved matter is decreased, and the Langelier index of drinking water can be improved.

Abstract: There is disclosed a method wherein sulfur dioxide contained in combustion exhaust gas is absorbed in an aqueous alkali sulfite solution to produce a corresponding alkali bisulfite and the resultant aqueous alkali bisulfite solution is added with calcium carbonate to form calcium sulfite, the method comprising wet-powdering the calcium carbonate into a particle size within a range of 0.1 - 30 .mu. in a slurry form by the use of a part of a filtrate which is obtained by separating calcium sulfite from the reaction solution, and re-using the remainder of the filtrate as an aqueous alkali sulfite solution for absorbing sulfur dioxide, whereby substantially no waste water is discharged out of the reaction system and sulfur dioxide can be recovered in the form of highly pure calcium sulfite.

Abstract: Process for through desulfurization of exhaust gas by treating the gas through the steps of absorption, double decomposition, oxidation, and alkali sulfate conversion.

Abstract: Sulfur dioxide can be removed from a combustion exhaust gas and converted to gypsum by first scrubbing a sulfur dioxide-containing combustion exhaust gas with an aqueous alkali sulfite solution to form an alkali bisulfite-containing aqueous solution and then treating, within a closed system, the thus formed aqueous bisulfite solution with a calcium compound. The efficiency of the sulfur dioxide removal can be increased greatly by adding a portion of alkali sulfite aqueous solution circulating in the system to at least a portion of filtrate from the gypsum separation process to precipitate metallic ionic impurities contained in the filtrate in the form of salts and separate these salts by filtration, and then recirculating the filtrate from the salt separation process to the absorption system.

Abstract: A method for effectively removing sulfur dioxide in the form of calcium sulfite from a combustion exhaust gas, comprising the steps of (1) feeding a portion of the combustion exhaust gas to a dilute sulfuric acid solution to produce sulfurous acid in the solution and oxidizing the resultant sulfurous acid with use of air or oxygen in the presence of an oxidizing catalyst to produce sulfuric acid; (2) feeding a residue of the combustion exhaust gas and the gas exhausted from the step (1) to an alkali sulfite aqeuous solution to produce an alkali bisulfite aqueous solution; (3) mixing a major portion of the alkali bisulfite aqueous solution produced in the step (2) with slaked lime or limestone for reaction to give a calcium sulfite-containing reaction solution; (4) separating calcium sulfite from the reaction solution obtained in the step (3); and (5) circulating the filtrate of the step (4) to the step (2) and mixing a minor portion of the alkali bisulfite aqueous solution produced in the step (2) with sulfur