Abstract: A method of producing cement or concrete, comprising the step of adding fly ash to the cement or concrete at the production stage, the fly ash containing lime and reaction products from the reaction occurring between lime and sulphur oxides in connection with the desulphuration of flue gases. To avoid the disadvantageous effects of calcium sulphite and entringite reactions and to increase the used amount of fly ash containing desulphuration waste, the calcium sulphite is oxidized by hydrogen peroxide either before the production of cement or concrete or during the production.

Abstract: A method for removing sulfur dioxide from flue gases, with oxidation of calcium sulfite in the discharge from a liquid scrubbing system to produce gypsum, oxidizes the sulfite in a thickener overflow at a pH of between 4.0 and 6.5. The calcium sulfite is oxidized to a calcium sulfate which precipitates from the aqueous media and is separated, while the acidic aqueous media is recycled to an acidification step preceding the oxidation. A further minor portion of scrubber slurry may be discharged from the liquid scrubber unit at a pH of 4.5 to 6.0 and also treated with acid, oxidized, and the resultant gypsum separated.

Abstract: The improved flue gas desulfurization process is effective for removing sulfur dioxide in the flue gas with a lime-bearing material in a fluidized lime reactor (50, 110, 164, 426). The effectiveness of the process is due primarily to the presence of sulfur trioxide in the gas, the sulfur trioxide being generated in a catalytic converter (40, 156, 418) and a bypass circuit (20, 408) transmitting a portion of the flue gas past the catalytic converter (40, 418). Sulfur trioxide may also be directly injected by duct injection in order to enhance the removal of sulfur dioxide from flue gas in the fluidized lime reactor (110, 164). In the initial phase, the duct injected sulfur trioxide efficiently raises the temperature of the lime-bearing particles (7) from the exothermic reaction with lime, resulting in the establishment of the steep temperature and sulfur oxides gradients which induce an autogeneous conversion of sulfur dioxide to sulfur trioxide.

Abstract: The present invention relates to the coproduction of a combustible gas stream usable as an energy source, a sulfur-dioxide-containing second gas stream usable as a source of oxidant in the gasification of coal, and a sulfur-dioxide-containing third gas stream usable as a feedstock for the production of sulfuric acid. The process includes heating coal in a coal gasification zone in the presence of an oxygen and sulfur dioxide-containing atmosphere under partial coal gasifying conditions to produce a carbonaceous char and a crude coal gas stream. Sulfur-containing compounds are removed from the coal gas stream and converted to elemental sulfur. The carbonaceous char is combined with gypsum to form a feed mixture. The non-gypsum portion of the feed mixture contains sufficient reducing potential to release substantially all of the sulfur in the gypsum as gaseous compounds of sulfur in a +4 or lower oxidation state.

Abstract: An improved process for economically and effectively granulating solid, finely-divided, particulate feedstock comprising phosphogypsum, limestone, or mixtures comprising sulfogypsum, natural or mineral gypsum, or mixtures thereof and limestone and having from about 80 to 95 percent by weight of such sulfogypsum/mineral gypsum to effect products which exhibit excellent physical and chemical properties relative to dustiness, storage, handling, and perhaps most importantly, aqueous media-induced rapidity of reversion to a mesh-size distribution of particles substantially similar to the initial size distribution of said feedstock, which improved process involves introducing such relatively finely-divided feedstock, together with material comprising recycle thereof into a suitable agglomeration device, such as a rotary drum, and therein effecting agglomeration/granulation of such feedstock in the presence of aqueous media, the improvement comprising the utilization, in combination with said aqueous media, of relat

Abstract: A pelletized mixture of gypsum, carbonaceous material and pyrite is charged to a travelling grate where the charge is heated under suitable conditions to produce a solid sintered material which has a broad spectrum of applications due to its chemical and physical properties and a gaseous effluent containing sulfur dioxide, sulfur or mixtures thereof.

Abstract: A process, and the product produced thereby, for the preparation of a waste solidification material from hardened fluorogypsum as a by-product of the manufacture of hydrofluoric acid by reacting fluorospar with sulfuric acid, removing hydrogen fluoride from the reaction product, slurrying the by-product with water, placing the slurried by-product fluorogypsum in settlement ponds until the fluorogypsum hardens, the hardened fluorogypsum having a pH of about 3 to about 5, including heating the hardened fluorogypsum to evaporate substantially all water physically mixed with the fluorogypsum and further heating the fluorogypsum to reduce the water chemically bound to calcium sulfate in the fluorogypsum to from about 0.5% to about 9% by weight.

Abstract: The present invention provides an aqueous dispersion comprising gypsum and a surface-active, anionic compound, wherein the surface-active compound is a phosphoric acid ester selected from the group consisting of (1) an acidic phosphoric acid ester of the formula: ##STR1## wherein R.sub.1 and R.sub.2 are the same or different and are alkyl poly(oxyethylene), alkyl poly(oxypropylene), alkylphenoxy- alkyl or alkylphenyl polyoxyalkyl radicals, (2) a monophosphoric acid ester of a mono- or dihydroxyalkylurea or of an alkoxylated mono- or dihydroxyalkylurea, and (3) a monophosphoric acid ester of a polyalkoxylated amine, in which several hydroxyl groups can be esterified with phosphoric acid.

Abstract: A coal fired power plant includes a coal gasification zone where coal is gasified in the presence of an oxidant-lean atmosphere under partial coal gasifying conditions to produce a carbonaceous char and a crude gas stream, an acid separating zone where sulfur-containing compounds are separated from the crude gas stream to produce a combustible gas stream, and a converting zone where the sulfur-containing compounds are converted to elemental sulfur. The combustible gas stream and the carbonaceous char are fed into a boiler which drives a generator to produce electricity; portions of the carbonaceous char product and the combustible gas stream are diverted into a gypsum desulfurization zone. SO.sub.2 -containing flue gas from the boiler is fed into a flue gas desulfurization zone. There, the SO.sub.2 -containing flue gas is contacted with lime and limestone to produce gypsum.

Abstract: A gypsum mold having good water absorbing properties, which is suitable for cast molding pottery, can be prepared by stirring a mixture of hemihydrate gypsum cooled to -40.degree. to 5.degree. C. and water to form a slurry of gypsum in water having a temperature of -5.degree. to 10.degree. C., pouring it into a water-impermeable mold, maintaining it therein until the setting reaction thereof is completed and then releasing the set product from the mold.

Abstract: In the desulfurization of flue gas utilizing limestone as absorbent in a double loop system, in which the flue gas is introduced into a quenching zone for contact with a first slurry of the limestone, and thereafter passes to an absorbing zone for further contact with a second limestone slurry, the two slurries being supplied from a mixing zone into which water and limestone are charged, and in which air is introduced into the quenching zone to convert the calcium sulfite present in it to gypsum, air is also supplied to the mixing zone to convert calcium sulfite in it to gypsum, and limestone is directly added to the quenching zone.

Abstract: P.sub.2 O.sub.5 values occluded in the crystals which are precipitated during the hemihydrate process for manufacturing phosphoric acid are recovered by dissolving and recrystallizing the hemihydrate crystals as dihydrate crystals in an acidic environment having a P.sub.2 O.sub.5 concentration of from about 0.1% to about 10% and a free sulfate concentration in the range of about 0.1% to about 10%. Water is used to wash the dihydrate filter cake, and the filtrate from this wash is used to redissolve the hemihydrate crystals. The free sulfate values are preferably supplied to the dihydrate crystallizer as sulfuric acid.

Abstract: The present invention relates to gypsum powders containing a hydrophobic agent and to water-repellent articles which are prepared from gypsum containing powered hydrophobic agents, in which the hydropohobic agents are prepared by spray-drying a mixture containing at least water, an organopolysiloxane having Si-bonded hydrogen and a water-soluble, film-forming polymer having a turbidity point of from 35.degree. to 98.degree. C.

Abstract: Disclosed herein is a method for producing .alpha.-form gypsum hemihydrate, comprising heating an aqueous slurry containing gypsum dihydrate and a salt of sulfosuccinic acid as the catalyst for crystallization, thereby converting gypsum dihydrate into .alpha.-form gypsum hemihydrate.

Abstract: Optimum overall operation of a whole plant including a combustion unit such as a boiler and a wet-process flue gas desulfurization unit comprising an absorption column for removing sulfur dioxide from a flue gas from the combustion unit by absorption using a slurry of an absorbing agent such as limestone powder circulated through absorption column, recycle pumps for circulating the slurry through the absorption column and oxidation air blowers for supplying an oxidation air to the absorption column and a recycle tank is controlled by anticipating a future pH value of the circulating slurry and a future inlet sulfur dioxide content of the flue gas from a present pH value of the circulating slurry and a present inlet sulfur dioxide content of the flue gas and their change rates by computing, anticipating a future desulfurization ratio from both the anticipated pH value and inlet SO.sub.

Abstract: A process is described for making flue gas gypsum from desulfurization of power plant exhaust gas. The process comprises treating the flue gas in a wash tower with a wash water suspension containing calcium oxide, calcium hydroxide or calcium carbonate and converting the scrubbed sulfur dioxide by oxidation with input atmospheric oxygen and by crystallization to calcium sulfate dihydrate crystals. A cyclic flow is drawn from the wash tower sump and delivered by spray nozzles to the wash tower. Further the process comprises continuously drawing an additional crystal suspension from the wash tower sump which after separation of a crystal slurry is partly fed back to the wash tower sump. The lower run-off of a cyclone separator receiving the crystal suspension is dewatered, the flue gas gypsum is separated and a clear effluent is returned to the wash tower. A partial flow is separated from the upper run-off of the cyclone separator and a solid free fluid replaces it.

Abstract: A process for the removal of heavy metals from an acid phosphate containing, liquid medium in which process a precipitate containing heavy metals is formed and is subsequently separated and wherein at least one of the two additives (a) sulphate ions and (b) calcium ions is added to the phosphate-containing, liquid medium under such conditions that a calcium sulphate anhydride-containing precipitate is formed.

Abstract: The present invention is concerned with a method for desulfurizing smoke which includes an absorbing procedure of cleaning a combustion exhaust gas with a limestone slurry; an oxidizing procedure of blowing air into the slurry coming from the absorbing process to oxidize calcium sulfite in the slurry to gypsum; a circulating process of circulating, through the absorbing procedure, the slurry coming from the oxidizing procedure; and a separating procedure of drawing a part of the slurry from the circulating procedure, separating and recovering gypsum therefrom, and returning the remaining slurry to the circulating system. The method is characterized in that a separator for separating the fed slurry into an over flow and an under flow is used, and the fed slurry is irradiated with ultrasonic waves to accelerate the separation of gypsum particles from limestone particles, whereby the limestone particles and the gypsum particles are transferred to the over flow and the under flow, respectively.

Abstract: A process for the production of highly concentrated phosphoric acid, comprises improvements in digesting phosphate rock with a mixed acid consisting essentially of sulfuric acid and phosphoric acid to obtain a slurry comprising phosphoric acid and hemihydrate (CaSO.sub.4.1/2H.sub.2 O), then filtering the slurry, taking out highly concentrated phosphoric acid as product acid and subsequently hydrating the hemihydrate to obtain gypsum (dihydrate: CaSO.sub.4.2H.sub.2 O).

Abstract: There is described a process which comprises adjusting on the one hand the flow rates of a circulating mixture relative to a base flow rate according to very specific specifications, and on the other hand so adjusting the reaction conditions in succeeding reaction zones as to obtain a production phosphoric acid with a P.sub.2 O.sub.5 concentration between 33 and 52%, and a H.sub.2 SO.sub.4 concentration between 0.25 and 2.5%, and calcium sulphate in the form of dihydrate, hemihydrate, anhydrite or a mixture of at least two said crystalline forms.

Abstract: The present invention relates to a process for the manufacture of disodium phosphate of a high purity without utilizing organic solvents. According to the process, monosodium sulfate is reacted, at a temperature, in the range of 40 to 100 degrees C. with a phosphate constituent selected from phosphate rock, dicalcium phosphate or mixtures thereof, in the presence of phosphoric acid. The common metal impurities, organic matter and fluorides present in the starting phosphate rock are substantially complete eliminated with the solid gypsum or dicalcium phosphate resulted thereto. After separating said solid, the filtrate is treated in two neutralization stages: first by a calcium constituent selected from calcium carbonate, calcium hydroxide or mixtures thereof and separating the formed dicalcium phosphate, followed by a second neutralization with an alkali sodium constituent selected from sodium hydroxide, sodium carbonate and sodium bicarbonate or mixtures thereof at a pH in the range of 8.0 to 9.5.

Abstract: A process is provided for preparing concentrated aqueous solutions of byproduct nitrate compounds from dilute aqueous streams containing said byproduct nitrate compounds, calcium ions and anionic species capable of reaction therewith at elevated temperatures. The process provides for the removal of the calcium ions by the addition of a source of carbonate ions to said stream to form solid, particulated calcium carbonate therein, the separation of the solid particulate from the stream, the neutralization of the stream and concentration of the stream to provide a concentrated aqueous solution containing the byproduct nitrate compound.

Abstract: A process for reducing sulfate ion concentrations in an alkali metal halide brine to be electrolyzed in an electrolytic cell comprises feeding the alkali metal halide brines to a reaction zone containing a slurry of gypsum crystals having a concentration of at least 5 weight percent of solids to form a brine-containing slurry. An aqueous solution of a brine soluble calcium salt is admixed with the brine-containing slurry in an amount sufficient to reduce the sulfate ion concentration to a desired level. The brine-containing slurry is agitated at a pumping velocity of at least about 1.0 meters per second to release solution supersaturation by gypsum crystal formation.

Abstract: Gypsum is calcined by contacting it with the hot gases spewing out of a combustion tube submerged in the mass of gypsum. The formation of dead-burned anhydrite is reduced by surrounding the combustion tube with a second tube called a draft tube. Gypsum passing through the annulus between the tubes is heated by the hot gases and is ejected from the annulus to prevent repeated excursions into the hot gas zone at the muzzle of the combustion tube.

Abstract: The present invention relates to the coproduction of a combustible feed gas stream useable as an energy source and a sulfur-containing second gas stream useable as a feedstock for the production of sulfuric acid. The process includes heating coal in the presence of an oxygen-lean atmosphere under partial coal gasifying conditions to produce a solid carbonaceous char and a crude coal-gas stream. Sulfur-containing compounds are removed from the coal gas stream and converted to solid sulfur-containing materials. The solid sulfur-containing materials are combined with the solid carbonaceous char and gypsum to form a feed mixture. The non-gypsum portion of the feed mixture contains sufficient reducing potential to release substantially all of the sulfur in the gypsum as gaseous compounds of sulfur in a +4 or lower oxidation state. The feed mixture is heated under reducing conditions to produce a sulfur-containing second gas stream and a solid sintered product.

Abstract: Hydrodynamic pumping of the fluidized calcining mass in a kettle is set up by the continuous flow of the mass to and from heating rods immersed therein which are constantly emitting at least about 1 British Thermal Unit of heat per minute per square inch of the surface of the rods. The transfer of heat from the walls and bottom of the kettle is enhanced so that more of the available heat is actually absorbed than in a kettle lacking such heating rods. The rate of calcination may be increased while the rate of heat input is decreased.

Abstract: High efficiency scrubbing of SO.sub.2 from stack gases by contact with a sodium based liquor is achieved by adjusting the pH of the scrubber liquor supplied to be in the range of 7.00 to 8.00; and a source of such liquor in a dual alkali system is disclosed in which a mixture of slaked lime and limestone is reacted with spent liquor in two stages one of which is at pH above 8.00, the other of which is at a pH below about 6.8 and the pH of the resulting regenerated liquor is adjusted to the desired pH range.

Abstract: A method of preventing scale and deposit formation on the surfaces of mist eliminators in wet scrubber flue gas desulfurization systems which utilize intermittent wash cycles which comprises coating the surfaces of these mist eliminators with a thin coating of talc.

Abstract: A continuous process for the manufacture of a metal salt solution is described which provides more economical products with higher quality than current processes. The process is safer, both to operating personnel and to the environment, than currently used processes. The process comprises feeding an aqueous metal compound slurry, e.g., a metal oxide/hydroxide slurry and a mineral acid, e.g., nitric acid, and water to a reactor which includes a zone of extreme mixing and agitation, most preferably a cross-pipe reactor provided with an optional static in-line mixer. A cross-pipe reactor provides complete and efficient reaction by providing greater surface area, high agitation and a long reaction time.

Abstract: Here is disclosed a method for treating SO.sub.2, SO.sub.3 and a dust simultaneously which comprises causing an exhaust gas containing at least SO.sub.2, SO.sub.3 and the dust to pass through a dry dust collector in order to remove most of the dust therefrom, delivering the exhaust gas to a gas absorbing device, and using at least one of calcium hydroxide and calcium carbonate as an absorbent in the gas absorbing device to remove SO.sub.

Abstract: The invention relates to a method and apparatus for desulfurizing flue gas n fuel oil firing systems comprising a residual heat exchanger forming an acid condensate. A neutralizing agent is added to the acid condensate and the neutralized condensate recirculated to the residual heat exchanger for the purpose of dissolving sulfur dioxide. The apparatus for carrying out this method in a fuel oil firing system comprising a residual heat exchanger and a collecting tank for the condensate is provided with a pump and a tank filled with neutralizing agent which are both disposed in a condensate recirculation conduit leading from the collecting tank to the residual heat exchanger.

Abstract: A flue gas desulfurization process by which gypsum can be recovered; the amount of water used therein is small, the effluent is treated in a closed system, the equipment used is minimized, and no scaling occurs; and an apparatus therefor are provided, the process including the following first process and second process: the first process comprising a cooling step of cooling and dedusting a SO.sub.2 -containing flue gas and removing acidic gases, an absorption step of contacting the cooled gas with a slurry containing limestone and lime to absorb and remove SO.sub.x and form CaSO.sub.3, a pH-adjusting step of adding H.sub.2 SO.sub.

Abstract: A dry particulate sulfite-containing material produced in a flue gas desulfurization process is oxidized and agglomerated in a fluidized bed reactor, wherein the material is fluidized in an oxygen-containing gas. The oxygen-containing gas which is supplied to the fluidized bed has a temperature below the agglomeration temperature of said particulate material. Due to the exothermic character of the oxidation, the temperature of the fluidized bed is maintained above the agglomeration temperature of the particulate material. Gas with entrained particles leaving the fluidzed bed are cooled during its passing through the freeboard of the fluidized bed reactor, whereby problems due to sticking of said entrained particles are avoided. At least a part of said entrained particles are recycled to the fluidized bed reactor.A fluidized bed reactor is provided suitable for performing the combined oxidation and agglomeration.

Abstract: The present invention is directed to a method for treating a waste gas to separate and recover gypsum and a dust therein, characterized by comprising the steps of causing the waste gas to pass through a dry dust collector; introducing the gas into a gas absorber, in which a slurry containing at least one of calcium hydroxide or calcium carbonate as an absorbent is employed to remove SO.sub.2 and the dust passed through the dry dust collector from the waste gas; blowing air into the resultant absorbing liquid in the gas absorber to oxidize the absorbing liquid and to thereby produce gypsum; delivering them to an absorbing liquid tank, in which the slurry mainly containing the gypsum grains is separated from the other slurry mainly containing the dust by partition walls disposed therein; and directly taking out the respective slurries separately from the absorbing liquid tank.

Abstract: A method of and an apparatus for the desulfurization of an industrial flue gas wherein the recirculating scrubbing liquid is sprayed with atomization into the scrubbing zone of a column and the droplet size, degree of atomization and gas flow velocity are controlled so that the pH of the scrubbing liquid within the scrubbing zone is substantially 3 to 6, preferably 4 to 5. In the sump oxidation is carried out by the introduction of oxygen to oxidize the calcium sulfite and calcium hydrogen sulfite which is formed to calcium sulfate.

Abstract: Desulfurization sludge from a flue-gas scrubber operating with calcium-containing additives is dewatered in a thin layer with precipitatable impurities in the liquid phase being precipitated out by neutralization and collected in a thin layer which is then rinsed. The presence of these precipitated impurities on the gypsum which is recovered by this process has not been found to be detrimental to the use of it as a construction material.

Abstract: Disclosed is a method of purifying by-product gypsum by making it into a sludge and washing the sludge in a single, multi-stage filtering washer. The washing liquid is recovered from the filtrate from the first stage of the washer and subject to neutralization in a two-stage neutralizing unit. The sludges separated in the neutralizing unit are dried and the excessive washing liquid from the second stage of the neutralizing unit is further processed in an evaporation stage.

Abstract: Spent absorbents resulting from desulfurization of flue gas in a spray drying-absorption process contain substantial amounts of sulfite, e.g. calcium sulfite. Said sulfite is oxidized into sulfate by heating of the spent absorbent in the presence of an oxygen-containing gas, preferably at temperatures of 350.degree.-600.degree. C. Thereby the spent absorbents may be converted into materials having industrial utility.

Abstract: Procedure and plant for spray drying absorption of flue gases by separation of SO.sub.2. A suspension of finely-ground limestone is added to a reactor via an oxidation and acidification unit, where the finely-ground limestone is mixed with recirculated solids and air, oxygen and/or some of the flue gases. Preferably, the recirculated solids is also subjected to reactivation by wet-grinding.

Abstract: The present invention provides a continuous method for preparing phosphoric acid and calcium sulphate by reacting calcium phosphate with a mixture of sulphuric acid and phosphoric acid. Our method uses at least three successive crystallization steps: a first step of reacting the phosphate with the mixture of phosphoric and sulphuric acids and forming a-hemihydrate calcium sulphate, a second step of recrystallizing the a-hemihydrate into dihydrate and a third step of transforming the dehydrated calcium sulfate into a hemihydrate or anhydrite II or a mixture of the two. Where desired recycling of the products from the above steps can be used for increasing the efficiency of the above method.

Abstract: Sulfur dioxide-containing effluent gases are desulfurized by contact with a slurry consisting essentially of water, a calcium compound selected from the group consisting of calcium oxide, calcium hydroxide and calcium carbonate, and an oxidizing agent selected from the group consisting of oxygen and hydrogen peroxide. In order to convert the sulfur dioxide to calcium sulfate of maximum particle size, the slurry is analyzed for content of said oxidizing agent, which is preferably maintained at a level to provide the oxidizing equivalent of an oxygen partial pressure of about 1-50 torr therein.

Abstract: A scrubber for flue gases from a fossil-fired power plant in which calcium sulfate dihydrate is produced by recirculating the scrubbing water suspension containing lime and introducing oxygen into the sump collection, has a discontinuously operated pump which withdraws the suspension for recovering of the solid product only discontinuously so as to maintain the solids concentration between 40 and 130 g/l.

Abstract: An apparatus and process for calcining gypsum is disclosed which utilizes a flash furnace for rapidly calcining fine particulate gypsum while the material is suspended in a stream of hot gas. The method and apparatus utilize a two-stage suspension preheater for utilizing waste gases from the calcining furnace for preheating raw material to be calcined and a two-stage suspension cooler for cooling hot calcined gypsum which is discharged from the calcining furnace. Spent cooling gas is supplied to the preheater for use in preheating the fresh gypsum to be calcined. The invention also contemplates recirculating a portion of the gypsum discharged from the furnace back to the furnace for further calcination. Hot product may be discharged directly from the furnace.

Abstract: A process for treating and recovering pickling waste liquids used for the pickling of stainless steel such as nitric-hydrofluoric acid, nitric acid, hydrochloric acid and, sulfuric acid is disclosed, which comprises recovering the nitric-hydrofluoric acid and the iron oxide or metallic ion from the waste liquids of nitric-hydrofluoric acid and nitric acid by two solvent extraction processes and recovering the Cr and Ni containing ferrite from the waste liquids of sulfuric acid or hydrochloric acid by a ferrite formation process. When the waste acid is sulfuric acid, gypsum of a high purity can be obtained.

Abstract: A method for treating the fine-grained spend absorbent (primarily calcium sulfite and calcium sulfate) from a dry flue gas desulfurization process. The absorbent, having a small amount of binder therein, is oxidized in a fluidized bed reactor at a temperature in the range from about 700.degree. C. to about 1000.degree. C. to produce a dry essentially fully oxidized pelletized calcium sulfate product.Calcium sulfate pellets having an average diameter of from about 0.5 mm to 5 mm and containing from about 1% to about 3%, by weight, of binder constituents, are composed of agglomerated calcium sulfate particles having an average diameter of from about 50.mu. to about 100.mu. bound to each other by the binder constituents.

Abstract: A method of and an apparatus for the desulfurization of the flue gases from a fossil fuel power plant. A particulate absorbent is contacted with the flue gases in a dry desulfurization step, particulates being then separated from the flue gas and being utilized in part as a secondary absorbent in a subsequent scrubbing of the flue gas. The sludge from the wet scrubbing is combined with the remainder of the dried particles from the separator to form a settable composition.

Abstract: A process for preparing shaped articles from waste gypsum from wet-process phosphoric acid production comprises:(1) mixing wet calcium sulfate hemihydrate with 0.5-20% by wt. of calcium hydroxide or calcium oxide,(2) adjusting the total water content of said mixture to 20-40% by wt., if necessary, and(3) molding shaped articles from said mixture by compression molding.The shaped objects so prepared have a low density and relatively high compressive strength.

Abstract: Wet chemical gypsum cake may be directly fed to a continuous kettle calciner to produce a stucco having lowered dispersed consistency. Pre-drying of the chemical gypsum is eliminated and the thus produced stucco may be used in the formulation of building plasters and in gypsum wallboard manufacture that will use less fuel for drying excess gauging water.

Abstract: An exhaust fume desulfurization process is disclosed which comprises the steps of contacting an off-gas containing SO.sub.2 with a slurry containing calcium and manganese compounds, introducing a gas containing oxygen into the slurry, detecting the amount of the absorption of oxygen by the slurry, and regulating the amount of manganese present in the slurry based upon the amount of oxygen absorbed by the slurry. The desulfurization rate is correspondingly adjusted and the desulfurized gas product is recovered.

Abstract: A process for manufacturing a cellular plaster with plaster obtained by calcining phosphogypsum, comprising mixing dry plaster with a previously prepared aqueous foam and with about 0.1-5% by weight, relative to the dry plaster, of slaked lime.