Abstract: Sulfur dioxide is removed from waste gases generated in a thermoelectric plant by contacting the gases countercurrently with an aqueous alkaline solution having a pH of about 9-12 and containing both sodium hydroxide and manganic hydroxide, whereby the sulfur dioxide reacts with the sodium hydroxide to form sodium sulfite until the pH of the solution is about 6-7 and the sodium hydroxide is substantially exhausted and wherein the sulfur dioxide then reacts with the manganic hydroxide to form manganese sulfite. The resultant sodium sulfite and manganese sulfite are oxidized and transformed into sodium sulfate and manganese sulfate respectively, by the action of oxygen in the mixture, in the presence of the manganic ion and also by the direct oxidizing action of the manganic ion.

Abstract: A method is disclosed for the acidulation of phosphate rock and the production of substantially pure alkali metal phosphates, calcium phosphates, and phosphoric acid which are essentially free of fluorides and recovery of the fluorine values from the starting phosphate rock in useful form. The steps of the method comprise initial acidulation of phosphate rock with a phosphoric acid solution containing sufficient alkali metal values to provide R.sub.2 O in the system, where R is alkali metal, to solubilize the phosphates and form an insoluble precipitate comprising a mixture of impurities, sand (SiO.sub.2) and the fluorides, from which the fluorides can be recovered in usable form. In preferred embodiments, after removal of the precipitate containing the fluorides, a portion of the solution of phosphoric acid and calcium phosphate is reacted with sulfuric acid and RHSO.sub.4 or R.sub.2 SO.sub.4 where R is alkali metal, to form a solution of RH.sub.2 PO.sub.

Abstract: Gas contaminated with at least one noxious component, such as SO.sub.2, HF or NO.sub.x, is scrubbed with a clear, calcium-containing, initially-basic washing liquid which also comprises the anion of a strong inorganic acid, that of a polybasic carboxylic acid and, optionally, that of a monobasic carboxylic acid. Apparatus is provided for scrubbing the gas, oxidizing produced calcium bisulfite to calcium sulfate, separating out and removing solids, and recirculating clarified liquid for scrubbing contaminated gas.

Abstract: In a process for preventing the formation of gypsum scale in a flue gas desulfurization process, in which a gas containing SO.sub.2 is subjected to a desulfurization treatment by a lime-gypsum process, the concentration of Ca(OH).sub.2 in an absorbing solution is maintained at not more than 0.1% by weight, and the absorbing liquid contains not more than 40% by weight of CaCl.sub.2.

Abstract: Molybdenum is recovered from dilute, ammoniacal, molybdenum containing solutions by adding ferrous ions to the solution to precipitate an iron hydroxide-ammonium molybdate complex. The precipitate is separated from the aqueous raffinate and is treated with acid to resolubilize the molybdenum in the complex. Molybdenum values are recovered from the resulting acid solution by ion exchange. The aqueous raffinate is purged of iron and is reused.

Abstract: A process for treating "brine mud" as produced in brine purification processes and for the coproduction of a calcium sulphate and magnesium carbonate which comprises(i) carbonating a slurry of "brine mud" in sodium chloride brine with carbon dioxide to produce a slurry of solids comprising calcium carbonate and a liquor comprising magnesium bicarbonate and sodium chloride.(ii) separating the slurry produced by the carbonation stage (i) into moist solid calcium carbonate and a liquor comprising magnesium bicarbonate and sodium chloride.(iii) heating the liquor from (ii) to produce a slurry of solids comprising magnesium carbonate, a liquor comprising sodium chloride, and gaseous carbon dioxide.(iv) separating the slurry from (iii) into moist hydrated magnesium carbonate and a liquor comprising sodium chloride and(v) drying the moist hydrated magnesium carbonate.

Abstract: This invention relates to a process for desulfurization of exhaust gases wherein the sulfur oxides are efficiently removed in the stabilized form from exhaust gases containing said sulfur oxides and at the same time gypsum of good quality is recovered. More particularly, this invention relates to a process wherein exhaust gases are treated with a slurried solution of gypsum containing a specified organic acid component, sulfuric acid component, and an alkali component at a pH value of 5-3 so that the sulfur oxides in said exhaust gases are absorbed and oxidized to form gypsum which is recovered as a by-product of good quality containing no unreacted lime.

Abstract: A process for the preparation of magnesium compounds from breunnerite or from mineral concentrates or tailings containing breunnerite in which the mineral is calcined and treated with an acid and the magnesium salt solution so formed is separated from insoluble matter.

Abstract: A method of beneficiating a mixed salt mineral ore containing potassium and magnesium sulfates and/or their hydrates which allows the recovery of anhydrous magnesium chloride and the simultaneous recovery of commercially acceptable potassium sulfate.

Abstract: Sulfur oxides are removed from a waste gas containing SO.sub.2 by: scrubbing the gas with an aqueous slurry containing Mg(OH).sub.2 as well as gypsum thereby to transform the SO.sub.2 into MgSO.sub.3 and to fix the same in this slurry; oxidizing the MgSO.sub.3 in this slurry to convert the same into MgSO.sub.4 ; filtering the slurry containing an aqueous solution of the MgSO.sub.4 thus formed and gypsum thereby to recover the gypsum; and adding Ca(OH).sub.2 to the aqueous solution of the MgSO.sub.4 of the filtrate thereby to convert, by double decomposition reaction, at least the greater part of the MgSO.sub.4 into Mg(OH).sub.2 and, at the same time, the Ca(OH).sub.2 into gypsum, the resulting aqueous slurry containing the Mg(OH).sub.2 thus formed as well as the gypsum being used for the above mentioned scrubbing of the waste gas. The double decomposition reaction in this process is carried out in the presence of seed crystals of gypsum to obtain gypsum of good quality.

Abstract: In a wet process using a steel slag for waste gas desulfurization, the desulfurization is carried out according to the following formula:log pH.ltoreq.-7.6.multidot.SO.sub.2 (%)/(O.sub.2 (%))+0.90,in which pH is the pH value of the aqueous slurry for absorption contained in an absorber; SO.sub.2 (%) is the concentration of the sulfurous acid gas contained in the waste gas at the inlet of the absorber; and O.sub.2 (%) is the concentration of the oxygen contained in the waste gas at the inlet of the absorber. This process has an excellent effect of desulfurization and an economical advantage.

Abstract: This invention relates to a process for desulfurization of exhaust gases containing sulfur oxides. More particularly, it relates to a process which can continuously put in operation to remove the sulfur oxides in exhaust gases in an efficient manner using a slurry of gypsum containing specified sulfate(s) within a single apparatus and can at the same time obtain gypsum as by-product.

Abstract: Aqueous glyoxylic acid solution is used to absorb sulfur dioxide and sulfur trioxide from a gaseous stream and the absorbed sulfur dioxide being removed from the aqueous glyoxylic acid solution by stripping and the absorbed sulfur trioxide being thereafter removed from the stripped glyoxylic acid solution. In a preferred embodiment, the absorbed sulfur trioxide is removed from the stripped glyoxylic acid solution by precipitation as barium sulfate. Particularly, sulfuric acid or absorbed sulfur trioxide in aqueous glyoxylic acid solutions may be removed by contacting the aqueous glyoxylic acid solutions with a barium compound such as barium hydroxide which is substantially inert to the glyoxylic acid but which precipitates barium sulfate from the aqueous glyoxylic acid solution.

Abstract: Processes for treating nitric effluents from plants so that a non-polluting stream is obtained and nitric values are recovered, which processes comprise acidifying nitric effluent, liquid-liquid extraction of the acidified effluent with an extraction agent comprising a neutral phosphoric ester and at least one long-chain alkylamine, and re-extraction of the loaded extraction agent with ammonia, thereby regenerating the extraction agent and providing ammonium nitrate, while at the same time providing a substantially nitric-free effluent.

Abstract: A process for exhaust gas desulfurization by the wet lime-gypsum process comprises an absorption step for scrubbing the exhaust gases with a calcium hydroxide slurry as an absorbent; an oxidizing step for oxidizing a slurry composed chiefly of calcium sulfite from the absorption step; and a solids-liquid separation step for separating a slurry composed mainly of gypsum from the oxidizing step, characterized in that the liquid from said solids-liquid separation step is passed into a sulfate impurity reaction step where said liquid reacts with added calcium hydroxide and is thereby freed from water-soluble sulfate impurities; and the so purified liquid is supplied to the absorbent preparation step where it is mixed with calcium hydroxide to form said absorbent. Also, precipitates formed in said sulfate impurity reaction step are supplied to said absorbent preparation step.

Abstract: A process for recovering aluminum from fly ash containing iron, silicon and titanium which comprises: (a) chlorinating the fly ash in an oxidizing atmosphere to selectively chlorinate and vaporize iron chloride from the remaining chlorides, (b) chlorinating the residue from step (a) in a reducing atmosphere of carbon monoxide, in the presence of added silicon chloride to suppress the chlorination of silicon, and vaporizing the chlorides of aluminum, silicon, titanium, and the residual iron, (c) separating and recovering the vaporized chlorides by selective condensation, and treating the residue of step (b) with sulfuric acid to convert calcium chloride to gypsum, and to regenerate a chloridizing and binder solution for pelletizing fly ash feed.

Abstract: An aqueous sodium chloride solution for use in production of caustic soda in an electrolytic cell having a cation exchange membrane is purified by adding to said solution a chemical reagent for precipitation separation of impurities remove silica through co-precipitation with a slurry of the precipitates of impurities which are circulated through said solution.

Abstract: The present invention provides a method for recovering vanadium from ferruginous chloride solutions by liquid-liquid extraction (or liquid ion exchange). Such chloride solutions are obtained in the extraction of vanadium from vanadiferous residues arising from the chlorination of titaniferous ores and in the extraction of vanadium from vanadiferous minerals. These solutions contain chlorides of vanadium, aluminum, iron, manganese and chromium. The method comprises adding sulfate ions to the chloride solution and recovering the vanadium by liquid-liquid extraction. By adjusting the sulfate-additive in relation to the concentrations of vanadium, iron and chloride in the solution vanadium can be exhausted substantially free from iron.

Abstract: A process for removal of particulate material and sulfur dioxide from a gas stream by washing the gas stream in a treatment zone in a wet scrubber by injection of a reactant such as high calcium or magnesium lime to control pH in the range of 6.0 to 8.5. A resultant slurry containing calcium sulfate, calcium sulfite and solids is formed in the scrubber and a controlled quantity of the solids containing slurry is recycled to the scrubber washing zone as part of the washing fluid to aid in co-precipitation by providing nucleation sites for the calcium sulfate and sulfite crystals maintaining an unsaturated calcium sulfate level in the slurry.

Abstract: Gypsum and magnetite which are both coarse and of good quality can simultaneously be produced by introducing calcium carbonate into an aqueous solution containing ferrous sulfate while an oxidizing gas is blown, and then carrying out a neutralizing and oxidizing operation at a pH of 5-6 and a temperature of 60-80.degree. C, and can be separately recovered by magnetic separation.

Abstract: The filtration rate and/or washability of crystals of gypsum produced during the wet process for the production of phosphoric acid are improved by adjusting the notional Al.sub.2 O.sub.3 :P.sub.2 O.sub.5 and reactive SiO.sub.2 :F ratios of the phosphate rock to within certain ranges. The adjustment may be achieved by addition of sources of aluminium and silica to the phosphoric acid process.

Abstract: In the process for the production of chlorine and alkali metal hydroxide by electrolysis according to the amalgam process using calcium- and/or sulphate containing crude salt, the calcium and/or sulphate contents introduced into the brine circuit by the crude salt are removed from the brine by precipitation of the double salt Na.sub.2 SO.sub.4 . CaSO.sub.4. Small particles of glauberite may be introduced to the brine to initiate and accellerate precipitation.

Abstract: Potassium sulfate is produced from a mixture of carnallite, potassium chloride, kieserite and residual quantities of less than 15% by weight of rock salt by treating the mixture at a temperature of 20.degree.-40.degree. C with potash magnesia liquor to form a slurry with at most 70 mole MgCl.sub.2 /1000 mole H.sub.2 O, whereafter the liquor portion of the slurry comprising a solution saturated with carnallite and rock salt is separated from the solid substance, which solid substance is then converted at temperatures of 75.degree.-110.degree. with a sulfate liquor, which contains 18-45 mole MgCl.sub.2 /1000 mole H.sub.2 O, into a mixture of langbeinite and potassium chloride, which mixture after separation from the liquor is treated at temperatures of 15.degree.-110.degree. C with a sulfate liquor containing 18-50 mole MgCl.sub.2 /1000 mole H.sub.2 O, whereupon the crystallizate is separated from the mother liquor and is converted with water to potassium sulfate.

Abstract: A process for the recovery of vanadium from acid sulfate solutions such as those derived by sulfuric acid leaching of industrial residues such as spent hydrodesulfurization catalysts, fly ash and furnace bottom ash in which magnesium oxide, hydroxide or carbonate is used as the neutralizing agent.

Abstract: Substantially pure magnesium hydroxide or carbonate is obtained from naturally-occurring minerals containing at least 10% magnesium silicate by adjusting the pH a magnesium bisulfite solution obtained therefrom to between 8.0 and 8.9 under an oxidizing atmosphere thereby to produce a magnesium sulfate solution from which the magnesium hydroxide or carbonate can be readily obtained.

Abstract: A process for the manufacture of calcium sulphate alpha-hemihydrate which comprises the step of interacting an aqueous solution of calcium chloride and a source of sulphate or bisulphate ions in an aqueous system at a temperature above the calcium sulphate hemihydrate/gypsum transition temperature under the reaction conditions. The preferred reagents are the waste calcium chloride/sodium chloride effluent of the ammonia soda process and sulphuric acid (e.g. impure sulphuric acid effluent) to give hydrochloric acid as a co-product. The preferred reaction temperature is at least 20.degree. C. above the transition temperature (about 70.degree. C), e.g. at 95.degree.-100.degree. C at atmospheric pressure.

Abstract: The invention is a method for working-up shale while recovering metals therefrom and the sulphur content thereof. The method comprises crushing the shale and leaching and roasting the shale. The sulphur content is oxidized and converted into sulphuric acid, concentrated sulphur dioxide or sulphur. The leaching operation is effected with sulphuric acid. The leached metals are recovered in a manner known per se and the residual solution is passed to the roasting stage.

Abstract: Sulfuric acid or absorbed sulfur trioxide in aqueous glyoxylic acid solutions may be removed by contacting the aqueous glyoxylic acid solutions with a barium compound such as barium hydroxide which is substantially inert to the glyoxylic acid but which precipitates barium sulfate from the aqueous glyoxylic acid solution. In a preferred embodiment, aqueous glyoxylic acid solution is used to absorb sulfur dioxide and sulfur trioxide from industrial flue gases and the absorbed sulfur dioxide being removed from the aqueous glyoxylic acid solution by stripping and the absorbed sulfur trioxide being removed from the stripped glyoxylic acid solution by precipitation as barium sulfate.

Abstract: A process for the purification of phosphate containing impure gypsum to obtain therefrom calcium sulfate semihydrate in a purified form by digesting the phosphate containing gypsum with nitric acid at a temperature between 22.degree. and 100.degree. C, the temperature and nitric acid concentration being regulated such as to dissolve most of the phosphate impurities and to allow the recovery of calcium sulfate semihydrate.

Abstract: Strontium values are recovered from a brine that contains strontium and calcium salts by admixing, with the brine, strontium sulfate seed and a water soluble sulfate and recovering the strontium sulfate that is thereby produced. The soluble sulfate should be more soluble in the brine than is SrSO.sub.4.

Abstract: In a method for oxidizing sulfur dioxide by contacting a sulfur dioxide-containing gas and an oxygen-containing gas with an aqueous solution containing pentavalent vanadium and divalent manganese as a catalyst, the method for regenerating and recycling the oxidation catalyst which comprises adding at least one calcium compound selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate and an oxygen-containing gas as an oxidizing agent to at least a part of the aqueous solution catalyst used in the oxidation reaction, separating the resulting gypsum, and recycling the recovered aqueous solution catalyst for use in the oxidation of sulfur dioxide.

Abstract: Sulfur dioxide is removed from stack gases by absorption in an aqueous medium, the preferred embodiment containing a chemical oxidant which generates hydrogen peroxide on a demand that equals the rate sulfur dioxide is absorbed into the medium whereby the absorbed sulfur dioxide is converted to sulfate form. The converted sulfur dioxide is removed in the form of an alkaline earth metal sulfate precipitate and spent oxidant is regenerated for reuse. In the other illustrated embodiments, the aqueous medium is maintained acidic from the start-up of the system. Barium peroxide is the preferred oxidant and acts both as oxidant and precipitant. Alternately, the oxidant and precipitant may be separate compounds.

Abstract: In an industrial process of preparing high-purity magnesia from an impure magnesium-containing starting material, wherein the starting material is dissolved in HCl and the resultant acidic solution is subjected to a multistep treatment for precipitating the impurities out of the solution, the precipitate is separated from the residual purified magnesium chloride solution, and the magnesium chloride is thermally decomposed to obtain magnesia, the purified magnesium chloride solution is first concentrated and sulfate ions are then added thereto to precipitate calcium ions from the concentrated solution as calcium sulfate.

Abstract: This invention relates to a process of producing magnesia from magnesium-containing carbonate ores, which comprises leaching with sulfuric acid, subsequently neutralizing the solution with magnesia, separating the undissolved impurities, crystallizing magnesium sulfate under pressure and above 150.degree. C so the crystals have from 1.5 to 4 moles of water per magnesium sulfate molecule and thermally decomposing the latter to form magnesia and SO.sub.2, recovering sulfuric acid from the sulfur dioxide produced in the decomposing steps and recycling the sulfuric acid to the leaching stage.

Abstract: Process for the recovery of pigment-grade iron oxide and technical hydrochloric acid of predetermined molarity, from iron chloride solutions such as pickling solutions containing hydrochloric acid. The iron chloride solution is concentrated until the molarity of the chloride ion therein is the same as the molarity of the hydrochloric acid which it is desired to produce. Concentrated sulfuric acid in slight stoichiometric excess relative to the iron, is then added to the iron chloride solution, which solution is thereafter evaporated to dryness. The distillation from this evaporation is hydrochloric acid of the predetermined molarity, and the dry residue is iron sulfate. The iron sulfate is calcined to drive off sulfur dioxide and sulfur trioxide and to leave iron oxide which may contain sulfates; and to remove these latter, the iron oxide is leached with dilute hydrochloric acid and is thereafter washed with water. The washed iron oxide is dried and micropulverized to produce a red iron oxide pigment.

Abstract: Scale is formed in a closed system wherein an exhaust gas containing sulfur dioxide is treated with an aqueous solution containing an organic acid alkali salt to remove the sulfur dioxide in the form of gypsum from the exhaust gas. The method disclosed herein prevents formation of scale in such a closed system.

Abstract: A method is disclosed for the acidulation of phosphate rock and the production of substantially pure alkali metal phosphates, calcium phosphates, and phosphoric acid which are essentially free of fluorides and recovery of the fluorine values from the starting phosphate rock in useful form. The steps of the method comprise initial acidulation of phosphate rock with a phosphoric acid solution containing sufficient alkali metal values to provide R.sub.2 O in the system, where R is alkali metal, to solubilize the phosphates and form an insoluble precipitate comprising a mixture of impurities, sand (SiO.sub.2) and the fluorides, from which the fluorides can be recovered in usable form. In preferred embodiments, after removal of the precipitate containing the fluorides, a portion of the solution of phosphoric acid and calcium phosphate is reacted with sulfuric acid and RHSO.sub.4 or R.sub.2 SO.sub.4 where R is alkali metal, to form a solution of RH.sub.2 PO.sub.

Abstract: Sulfur dioxide is separated from an aqueous solution containing the same by subjecting the stream to electrodialytic water splitting. In particular a novel method for removing SO.sub.2 from dilute gas streams by means of alkaline solution scrubbing, regeneration of the scrubbing solution and liberation of concentrated SO.sub.2 effected by means of a two-compartment membrane water splitter is provided. Optionally, waste sulfate produced in the process may be converted to sulfuric acid in a separate membrane water splitter or otherwise processed by conventional means.

Abstract: A method of desulfurizing exhaust gases by a wet lime-gypsum process comprises the steps of neutralizing a suitable amount of liquid containing impurities separating the neutralized material into solid and liquid phases, heating the separated solid phase to dryness while concentrating the separated liquid phase, mixing the concentrated liquid and dried solid phase in such a manner that the resulting mixture exists as a solid mass containing the impurities, thus making it unnecessary to dispose of any waste liquid.

Abstract: The invention is concerned with improved process and apparatus for the removal of sulphur dioxide from flue gas or other waste gas of the kind in which the waste gas is scrubbed by a circulating wash liquid containing lime suspensions, i.e. suspensions of calcium oxide, hydroxide or carbonate, the calcium/sulphur compounds so formed being oxidized and removed from the circulation, the improvements of the present invention comprising primarily the freeing of the wash liquid from solid matter before contact with the waste gas and then the control of pH values of the wash liquid at different stages of the circulation to facilitate, for example, the oxidation of the particular calcium/sulphur compound, formed in the scrubbing process, to calcium sulphate, the apparatus also being designed to improve the oxidation step.

Abstract: In the electrolysis of an alkaline earth metal-containing alkali metal brine wherein the alkaline earth metals contained in the brine are removed, the brine is subjected to electrolysis, and the residual brine is concentrated and recycled for further electrolysis along with make-up fresh brine, the improvement which comprises contacting the alkaline earth metal-containing brine with a weakly acidic cation exchanger in the Na+ form, the exchanger comprising units of at least one of acrylic acid and methacrylic acid, whereby the alkaline earth metals are adsorbed on the cation exchanger, and periodically regenerating the cation exchanger. The cation exchanger is regenerated by contact with a hydrochloric acid solution of about 5 to 10% concentration, the regenerating solution effluent from the column being combined with the redissoluted sodium sulphate which is precipitated during concentration of the cell liquor thereby to precipitate any sulphate contained in the brine as the alkaline earth metal sulphate.

Abstract: A method of desulfurizing exhaust emissions which comprises pulverizing slag from a blast furnace, converter, open-hearth furnace or the like which is composed principally of Ca.sub.2 Al.sub.2 SiO.sub.7, suspending the resulting minute particles in water, and bringing the aqueous suspension of pulverized slag into contact with the exhaust that contains sulfur dioxide and oxygen, while supplying the slag at a rate to keep the pH of the suspension within a range of 1.5 to 4.0 and thereby to remove the sulfur dioxide from the exhaust.

Abstract: A process for producing .alpha.-type hemihydrate calcium sulfate by oxidizing calcium sulfite with an oxidizing agent in a suspension containing at least one anionic, nonionic or amphoteric surface active agent.

Abstract: This disclosure is concerned with the demineralization of crustacea shells and the like, before or after protein removal therefrom, with sulfurous acid, thus to convert the calcium carbonate of the shell to calcium bisulfite solution which may be separated from the solid residual shell, and regenerating sulfurous acid from the said solution for reuse in the process.

Abstract: A filler for a mica-free joint compound, comprising by-product gypsum having a mean particle size between about 11 and about 12 microns, a percentage by weight of particles smaller than 1 micron of between about 5 and about 6.5, and a packed dry bulk volume no greater than about 93 cc. per 100 grams.

Abstract: In a method for removing sulfur oxides in a stack gas by absorbing the sulfur oxides in an absorbent comprising predominantly calcium compounds, thereby converting the sulfur oxides to sulfites, and then oxidizing the sulfites to gypsum, the improvement where the absorbent further contains a magnesium compound such as Mg(OH).sub.2, MgCO.sub.3 or MgSO.sub.4.

Abstract: Calcium sulphate produced by reacting crude phosphate with sulphuric acid is washed with aqueous solutions of condensed and complex aluminium fluorides of the general formulae MeAlF.sub.4, Me.sub.2 AlF.sub.5 and Me.sub.5 Al.sub.3 F.sub.14 as well as AlF.sub.3.nH.sub.2 O, in which Me represents an alkali metal, ammonium or thallium-I ion and n is a number between 1 and 9.

Abstract: In the scrubbing of sulfur compound containing stack gases, there is an advantage to converting calcium sulfite to calcium sulfate downstream from the scrubber in order to provide for smaller sludge handling equipment and to form a more usable sludge. Thus, in the present operation, there is provided an ozonation of the withdrawn scrubber bottoms slurry to effect the conversion of calcium sulfite in such slurry to calcium sulfate.

Abstract: Sulfate solutions containing at least one valuable metal from the group: Fe, Ni and Co, particularly solutions resulting from the leaching of lateritic ores or concentrates, are treated to recover the valuable metal. The latter is precipitated by treating the solution with magnesium hydroxide. The resulting magnesium-containing solution is treated with lime under controlled conditions to precipitate relatively fine particles of magnesium hydroxide and relatively coarse particles of gypsum. The difference in particle size is relied on to separate the magnesium hydroxide (for recycling) from the gypsum (which is calcined to regenerate lime).

Abstract: A process, in which sulfur dioxide gas contained in waste gas is removed therefrom and collected as gypsum. In said process, the waste gas is subjected to a flow of detergent solution of basic aluminium sulfate so that the sulfur dioxide is absorbed into the solution. This solution, now containing the sulfur dioxide, is thereafter subjected to oxidation, resulting in a decrease in the basicity thereof. The solution is then neutralized by calcium carbonate or calcium hydroxide, whereby gypsum is precipitated in the solution and collected therefrom and whereby the crude content of the solution is recovered so that it may be used again as a detergent for the waste gas.