Abstract: A method of preparing precipitated calcium carbonate which comprises slaking quicklime in an aqueous medium, passing the suspension of calcium hydroxide through a sieve having an aperture size in the range of 40 to 70 microns, carbonating the calcium hydroxide and separating the calcium carbonate from the aqueous medium in which it is suspended. The sieved calcium hydroxide is subjected to high energy, high shear agitation which is terminated prior to carbonation. During the carbonation, the suspension of calcium hydroxide is subjected to relatively lower energy and shear agitation compared to the previous high energy, high shear agitation.

Abstract: A process for producing rhombic or barrel shaped precipitated calcium carbonate. Quicklime is slaked in an aqueous solution containing about 0.1% to about 2% by weight of a sugar, based upon the weight of the CaCO.sub.3 to be produced. Carbon dioxide is added to the slaked lime slurry at a preferred temperature of about 50.degree. F.-70.degree. F. until the pH drops from about 11-12 to about 7-8.

Abstract: A process for disaggregating boronatrocalcite ore (Ulexite) in an alkaline aqueous medium for the production of sodium borate and calcium borate, characterized in that boronatrocalcite is dispersed in alkaline mother liquor having a H.sub.3 BO.sub.3 /Na.sub.2 O weight ratio ranging from 1.8 to 2.7, at a temperature of 120.degree.-200.degree. C. under autogenous pressure of 2-16 bars, under intense stirring.

Abstract: This is a process and a device making use of a process for forming calcium oxide from pulverulent calcium carbonate, according to which an initial bath of pulverulent calcium oxide is produced in a reactor (1, 31) in the form of a fluidized bed which is heated electrically to a temperature higher than of the order of 900.degree. C., and the said pulverulent calcium carbonate is then introduced continuously into the bath while the temperature of the bath is always kept higher than of the order of 860.degree. C. by electrical heating, to dissociate the said calcium carbonate into calcium oxide and carbon dioxide.

Abstract: The processing of leaching residues from barium sulfide leaching is described. Sodium sulfide as well as a solid which is useful as an additive for fired clay products, particularly bricks, are obtained as valuable reaction products.

Abstract: This invention relates to a method for toxicity comprehensive elimination of chrome residues, comprising adding water to chrome residues, wet-grinding the same to a thick liquid, letting it react with dilute hydrochloric acid, and letting the filtrate obtained react with an additive containing barium, with sulfuric acid or magnesium sulfate, and with cream of lime or soda, so as to realize a comprehensive extraction and utilization of various elements. The hydrochloric acids can be circulated, and the filter residues can be used for iron-smelting and brick-making. By means of this method, it is possible not only to completely and permanently eliminate the toxicity of the residues, but also to realize a comprehehsive utilization of the residue resources.

Abstract: In the manufacture of ammonium paratungstate, sulfide is added to a tungsten-containing solution in order to precipitate molybdenum sulfide. Volatiles, including sulfides, evolved during this process are collected in a caustic scrubbing solution. The sulfide values in the caustic scrubbing solution may be reused to precipitate molybdenum sulfide by first treating the caustic scrubbing solution with alkaline earth chloride or sulfate to precipitate out alkaline earth carbonate.

Abstract: The invention process provides a metal oxide, or oxides of more than one more metal, wherein the oxides have a mean particle size less than 1 micron. The oxides are made by steps including (1) reacting an aqueous solution of a metal salt (or salts) that form insoluble carbonate(s), thereby to form a carbonate precipitate, followed by (b) recovering the precipitate, e.g., by filtration; (c) redispersing the precipitate in water to form a second very dilute slurry; (d) spray-drying said second slurry; (e) calcining the spray-dried product at a low temperature (e.g., 540.degree. C.), followed by a final calcination in atmosphere consisting of flowing oxygen initially under reduced pressure (e.g., 2 Torr). The spray-dried spheroids comprise particles having a mean particle size less than one micron, a property carried over into the products of both calcinations.

Abstract: A colored precipitated calcium carbonate having a strong color fastness in water is produced by preparing an aqueous slurry containing calcium hydroxide and a water-soluble dye, for example, a direct dye, introducing a carbon dioxide-containing gas into the aqueous slurry, and collecting the resultant colored precipitated calcium carbonate from the aqueous slurry at a pH of 8.2 or more thereof.

Abstract: The invention provides a method for the preparation of a calcium carbonate powder of which the particles have a platelet-like particulate configuration and which is useful as a pigment or filler in various products with superiority to kaolin clays and mica powders. The method is a two-step carbonation method of a milk of lime of which the first step is performed by blowing carbon dioxide into the milk of lime until 10 to 70% of the calcium hydroxide is carbonated and the second step is performed by admixing the thus partially carbonated milk of lime with an aqueous carbonating solution containing an alkali metal carbonate or ammonium carbonate and an alkali metal hydroxide or ammonium hydroxide in specified concentrations to complete the carbonation of the calcium hydroxide.

Abstract: The present invention is directed to an improved method for carrying out a exothermic chemical reaction with carbon dioxide in an aqueous environment. In the method, a fluid solution containing at least one chemical reactant which is exothermically reactive with carbon dioxide is provided. Liquid carbon dioxide is then injected into the solution of the chemical reactant at a pressure above the triple point of at least about 60 psig. The injection of the liquid carbon dioxide takes place under turbulent conditions wherein the liquid carbon dioxide expands to provide carbon dioxide vapor. The carbon dioxide vapor superheats to approach the exothermic reaction temperature which occurs between the carbon dioxide vapor and the chemical reactant. The chemical reactant and the carbon dioxide react in the dispersion exothermically to produce a chemical reaction product.

Abstract: An improved method for causticizing the green liquor formed in a kraft paper plant by contacting the green liquor with lime to thereby form white liquor followed by clarifying the white liquor by removing the lime mud therefrom in a clarifier is disclosed wherein the improvement lies in removing the lime mud from the clarifier at a predetermined rate.

Abstract: A precipitated alkaline earth metal carbonate is produced by calcining raw alkaline earth metal carbonate, for example a calcium carbonate, under conditions such that substantially all the chemically combined carbon dioxide is driven off to form an oxide, slaking the oxide in water to form a suspension of the corresponding alkaline earth metal hydroxide, allowing the suspension to cool to 45.degree. C. or below, and then carbonating the hydroxide in suspension in water with substantially pure carbon dioxide in the presence of a dithionite bleaching reagent to form a precipitate of an alkaline earth metal carbonate of increased brightness and purity. The precipitate may then be separated from the aqueous medium by, for example, filtration.

Abstract: Process for causticizing a water solution containing alkali carbonate with calcium oxide and hydroxide by bringing the water solution containing alkali carbonate into contact with the calcium oxide or hydroxide and by separating the alkali hydroxide solution arisen in the causticizing from the calcium carbonate precipitate. The water solution containing alkali carbonate is conducted through a bed which has been formed by mixing calcium oxide and calcium carbonate in the causticized alkali solution and by removing the excess alkali solution.

Abstract: Dibasic carboxylic acids or salts thereof are used to remove metals, particularly calcium and iron, from hydrocarbonaceous feedstocks. An aqueous solution of the acid is used to extract the metals from the feedstock prior to processing. Oxalic acid is the preferred compound.

Abstract: Purified barium salts essentially devoid of strontium impurities, e.g., highly pure barium carbonate, are produced by liquid/liquid extracting an aqueous solution of impure barium values with an organic solvent medium which comprises at least one water-insoluble carboxylic acid, phosphonic acid monoester, or substituted 8-hydroxyquinoline extractant. The mixture of extraction is separated into a purified aqueous phase containing the desired barium salt values and an organic phase containing the impurity values sought to be removed.

Abstract: Disclosed is a novel process of producing needle-shaped calcium carbonate particles. In the process of the present invention, aqueous calcium hydroxide solution is added to an aqueous medium bath with a temperature of not less than 60.degree. C. into which carbon dioxide gas or a carbon dioxide-containing gas is being blown to generate needle-shaped calcium carbonate particles. The temperature of the aqueous medium bath is kept not less than 60.degree. C. during the addition of the aqueous calcium hydroxide solution. Then the generated needle-shaped calcium carbonate particles are recovered.

Abstract: Barium compounds containing contaminating amounts of strontium, e.g., barium salts, are effectively purified, notably into barium values suitable for conversion into specialty grade barium carbonate and titanate, by intimately contacting and liquid/liquid extracting aqueous solutions thereof with an organic solvent phase comprising at least one essentially water insoluble --CH.sub.2 --R' substituted 8-hydroxy-quinoline extractant.

Abstract: A process is disclosed for removing metals contaminants, particularly calcium compounds, from hydrocarbonaceous feedstocks using aqueous carbonic acids, its salts, or mixtures thereof as the metals extraction agent. The hydrocarbonaceous layer and aqueous layers are then separated and the demetalated hydrocarbonaceous feedstock is removed for further processing.

Abstract: A process is disclosed for the removal of metals contaminants, particularly calcium, from hydrocarbonaceous feedstocks. The process comprises mixing the feedstock with an aqueous solution of a metals sequestering agent, particularly hydroxocarboxylic acids, especially citric acid, then salts or mixtures thereof, and separating the aqueous solution containing the metals from the demetalated feedstock.

Abstract: A process is disclosed for the removal of metals contaminants, particularly calcium, from hydrocarbonaceous feedstocks. The process comprises mixing the feedstock with an aqueous solution of a metals sequestering agent, particularly amino-carboxylic acids, their salts, or mixtures thereof, more particularly EDTA, and separating the aqueous solution containing the metals from the demetalated feedstock.

Abstract: A process is disclosed for the demetalation of organically-bound compounds of Group VIII metals, particularly iron, from hydrocarbonaceous feedstock. In the process, an aqueous solution of amino-carboxylic acid, or salts, particularly EDTA, is used to form complexes with the metals and extract them from the feedstock. The aqueous phase containing the complexed metals contaminants is then separated from the hydrocarbonaceous phase.

Abstract: Carbonate-containing mineral fillers, pigments and similar materials are disclosed which are characterized by a combination of four features. These carbonate-containing materials can be used in particular in dyes, paints, paper pulps, paper coatings and plastics to great advantage. In addition, a method of preparing these carbonate-containing materials is disclosed.

Abstract: Process for removing Sr and heavy metals from water in particular from waste water by throughly mixing it with a solution of an alkali metal carbonate and/or hydrogen carbonate in a reactor containing a fluidized bed of suitable bed material. The obtained heavy metal carbonate crystals crystallize onto said bed material and the obtained heavy metal carbonate crystals in granular form are removed from the reactor from time to time.The heavy metals which may be removed are Ni, Zn, Cu, Fe, Ag, Pb, Cd or Hg.

Abstract: The invention concerns a causticizing procedure by which from soda liquor derived from a sulphate cellulose digesting process and from unslaked lime is produced white liquor for reuse in the digesting process, over lime slaking and a subsequent causticizing reaction proper. It is essential in the invention that the lime slaking is carried out using white liquor, whereafter the causticizing reaction proper is allowed to take place between the slaked lime and soda liquor combined therewith. The requisite white liquor is obtained by recirculating part of the white liquor produced by the causticizing process, to the slaking step, where it either completely or partially replaces the soda liquor employed in prior art. By using white liquor, one avoids the foaming, interfering with the process, which is encountered in the slaking step.

Abstract: Dry, stable carbonating agents comprised of a carbohydrate/metal bicarbonate complex are disclosed. The complex is prepared by reacting a carbohydrate with a metal hydroxide or oxide at a temperature not exceeding 25.degree. C. to form a carbohydrate/metal hydroxide adduct to which carbon dioxide is then introduced to form the complex. The complex is then immediately dried, preferably by freeze drying. The carbonating agents are particularly useful as components of dehydrated beverage powders. Upon rehydration, the complex releases carbon dioxide and carbonates the beverage. Additionally, upon rehydration the complex promotes the solubilization of the carbohydrate components in the beverage.

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: High purity magnesium oxide is obtained from a magnesite-containing ore, the impurities of which include calcium compounds. The ore is first calcined and the resulting magnesium oxide is converted to magnesium chloride by leaching with an ammonium chloride solution. Calcium chloride is also produced at the same time. The resulting magnesium chloride and calcium chloride are treated with carbon dioxide to form calcium carbonate and magnesium carbonate which can be precipitated and filtered out of the resulting magnesium chloride solution. The magnesium chloride solution is then reacted with ammonium carbonate to produce a magnesium carbonate trihydrate crystal slurry containing ammonium chloride. The ammonium chloride is subsequently removed and returned to the ammonia recovery stage for leaching of the calcined magnesium oxide while the crystals are dried and decomposed into carbon dioxide and magnesium oxide.

Abstract: Spent flux containing calcium oxide and calcium sulfide, recovered from the reduction of iron ore, is carbonated, as an aqueous slurry, in two stages, with the first stage being operated at a pH to prevent reaction of calcium sulfide, and the second stage being operated at a pH at which calcium sulfide is reacted to produce an effluent gas containing hydrogen sulfide.

Abstract: A process for producing highly pure magnesium hydroxide, which comprises reacting magnesium hydroxide starting material containing impurities, with an aqueous solution containing a water-soluble calcium salt and carbon dioxide to form an aqueous solution containing a magnesium salt and calcium carbonate precipitates whereby said impurities are transferred to the precipitates, filtering off the precipitates, then reacting the aqueous solution containing the magnesium salt, with ammonia to form a slurry comprising magnesium hydroxide solid and an aqueous solution containing an ammonium salt, and filtering the slurry to obtain highly pure magnesium hydroxide solid and an aqueous solution containing the ammonium salt.

Abstract: A process of recausticizing kraft green liquor in which the green liquor containing sodium carbonate is passed in a stream in admixture with particles comprising slaked lime, in which stream the liquid phase becomes progressively weaker in sodium carbonate and stronger in sodium hydroxide. Lime is added in order to provide a continuous supply of slaked lime for reaction with the sodium carbonate, and the stream is passed to a solids/liquid separator which recovers liquid phase from said stream, strong in NaOH, continuously and separately from the solid phase of the stream, as white liquor. The rate of the recausticizing reaction is limited by the rate of diffusion of carbonate ion into the solid particles, and of hydroxyl ion out of the solid particles. Typically, these rates limit the amount of causticizing achieved to less than the equilibrium value.

Abstract: Essentially pure strontium carbonate is recovered from low to medium grade strontium sulfate containing ores by first treating the ore with a hydrochloric acid solution to remove extraneous materials including calcium, magnesium, barium, and iron. The remaining strontium sulfate containing residue is treated with ammonium carbonate to produce insoluble strontium carbonate and soluble ammonium sulfate. The strontium carbonate then is converted to soluble strontium chloride through treatment with a second, stronger hydrochloric acid solution. Any remaining extraneous barium or iron is removed from the second acid solution before the strontium chloride is reconverted to insoluble strontium carbonate and precipitated out of solution for recovery.

Abstract: Very pure magnesium oxide is obtained from ore containing magnesium, more particularly ore containing magnesium carbonate, by calcining the ore and leaching the resulting magnesium oxide with carbon dioxide and calcium chloride solution to produce magnesium chloride solution. Carbon dioxide and ammonia are added, so as to precipitate magnesium carbonate trihydrate, which is decomposed to magnesium oxide.

Abstract: A process for extracting arsenic from aqueous solution to be purified, in accordance with claim 1 of U.S. Pat. No. 2,404,601, which also contains alkali metal carbonate, sulphate, hydroxide or hydrogen carbonate, and which may also contain at least one of the metals vanadium, uranium and molybdenum, comprising caustification of said solutions by means of lime to convert the carbonates into alkali metal hydroxides, followed by separation of an alkali metal hydroxide-enriched liquor and a first precipitate essentially containing calcium carbonate which is subjected to a washing operation, concentration by evaporation of the mixture of the washing liquor of the first precipitate to produce a second precipitate which essentially comprises alkali metal sulphate, which is characterized in that, before the aqueous solution is caustified, the aqueous solution is treated by a magnesium compound in an amount at least equal to the stoichiometric amount required to cause precipitation of magnesium arsenate.

Abstract: Magnesium is removed from brine by contacting the brine with calcium hydroxide at temperatures above about 80.degree. C. but below the boiling point of the brine. The contacting results in the formation of magnesium hydroxide precipitate which is substantially insoluble in the mother liquor at those temperatures and strontium hydroxide which is dissolved in the mother liquor. When the contacting is carried out at a temperature above about 90.degree. C., magnesium hydroxide precipitate is fast settling and filterable; accordingly, it is removed from the mother liquor by a conventional process, such as filtering. The mother liquor is then cooled to cause the precipitation of at least a substantial part of strontium hydroxide present in the mother liquor. The precipitate of strontium hydroxide is recovered by a conventional process such as filtering. If precipitation upon cooling is insufficient, carbon dioxide gas is introduced into the mother liquor to effect the precipitation of strontium hydroxide.

Abstract: Heat treated anionic clay mineral is an improved catalyst for the conversion of acetone to mesityl oxide and isophorone as well as for the aldo condensation of other carbonyl-containing compounds.

Abstract: A process for the purification of solutions containing sodium or potassium carbonate, sulphate, hydroxide or hydrogen carbonate, and mainly at least one of the metals belonging to the group formed by vanadium, uranium or molybdenum, in the form of sodium or potassium salts, and inorganic and/or organic impurities, wherein the above-mentioned solutions are completely or partially caustified by the addition of an adequate amount of lime, whereby a first precipitate essentially containing calcium carbonate is separated, and the separated liquor is concentrated by evaporation until the hydroxide content is at most equal to 50%, to cause the production of a second precipitate which essentially comprises sodium or potassium sulphate, then, after separation thereof, a hydroxide-rich liquor is collected.This process is more particularly adapted for treatments of liquors resulting from the alkaline attach of vanadiferous and uraniferous ores.

Abstract: Strontium carbonate is prepared by the process of reacting strontium nitrate in an aqueous reaction medium with carbon dioxide to precipitate strontium carbonate product, the nitric acid byproduct that forms being neutralized by the introduction of lime to the reaction medium.

Abstract: A method for recovering a magnesium carbonate of high purity from an aqueous magnesium hydroxide slurry is disclosed. The slurry contains at least 1 percent of magnesium hydroxide and consists of water, magnesium hydroxide and impurities normally associated with magnesium hydroxide slurries. The method involves carbonating the slurry with sufficient carbon dioxide to dissolve a substantial proportion of the magnesium hydroxide therein as magnesium bicarbonate, continuing carbonation until a solution saturated with magnesium bicarbonate is formed, a portion of the magnesium bicarbonate is converted to a crystalline magnesium carbonate and substantially all dissolved calcium is precipitated, so that the slurry contains dissolved magnesium bicarbonate, a crystalline magnesium carbonate precipitate and a calcium carbonate precipitate.

Abstract: A process for the purification of salt brine having magnesium and calcium hardness includes the steps of treating a saturated salt brine containing magnesium and calcium ions with an alkali metal carbonate and an alkali metal hydroxide in a preselected sequence and in amounts in excess of stoichiometric proportions to form firm, readily settleable, filterable floc precipitate particles of insoluble compounds of magnesium and calcium, suspended in the treated brine and passing the resultant suspension to a filtering unit to separate and remove the floc precipitate and to provide a purified salt brine.

Abstract: A method for leaching magnesium from a magnesium hydroxide-containing composition, especially a mineral, which comprises contacting said composition with an aqueous solution of an ammonium salt whose corresponding magnesium salt is soluble in said aqueous solution to thereby produce said soluble magnesium salt; separating said aqueous solution from said composition; and transforming the magnesium of said soluble magnesium salt into an insoluble magnesium compound. The method is particularly useful for leaching magnesium from brucite-containing chrysotile asbestos fibers, to yield both a magnesium compound and brucite-free, dispersed chrysotile fibers.

Abstract: A process for reducing calcium ion concentration in alkaline alkali metal chloride brines containing an alkali metal hydroxide is disclosed. The process comprises admixing an alkali metal bicarbonate with the alkaline brines to form an insoluble calcium salt, removing the insoluble calcium salt from the brine, and recovering a purified alkali metal chloride brine having reduced calcium ion concentration.The process produces alkali metal chloride brines suitable for use in electrolytic diaphragm cells while substantially reducing the amount of acid required to neutralize the brines.

Abstract: A chemical, electro-chemical process for recovering meta values from a zinc- or lead-containing material comprises:in a solubilization stage, oxidizing the zinc- or lead-containing material by treating said material with a ferric chloride leach solution;when solubilized lead is present, separating it from the pregnant liquor forming an essentially lead free solution;dividing this essentially lead free solution into two portions;passing one portion of the essentially lead free solution into the anolyte compartment of a Zn.degree. producing electrolysis stage for use as the ferrous ion-containing anolyte thereof;separating iron from the second portion of the essentially lead free solution, forming an essentially iron free solution;passing the essentially iron free solution into the catholyte compartment of said Zn.degree. producing electrolysis stage for use as the catholyte thereof;conducting electrolysis in said Zn.degree.

Abstract: A method of producing magnesium sulphate comprises the steps of interacting ferrous sulphate with compounds including magnesium carbonates, oxides and hydroxides, with magnesium sulphate being produced. The step of interacting the starting reagents is conducted in water medium in the presence of carbon dioxide and is effected in the range of temperatures of 80.degree. to 100.degree. C.

Abstract: Aqueous waste streams containing recoverable chlorine are reacted with an aqueous solution of an alkali metal hypohalite, such as sodium hypochlorite, to form an aqueous salt solution of an alkali metal halide, such as sodium chloride, and an alkaline earth metal hypohalite, such as calcium hypochlorite. Thereafter the aqueous salt solution is admixed with an organic alcohol to form an organic-aqueous salt solution. A gas containing chemically bound oxygen, such as carbon dioxide, is reacted with the organic-aqueous salt solution to form a slurry of solid particles of calcium carbonate suspended in a liquid mixture. The solid particles of calcium carbonate are separated from the liquid mixture.The aqueous phase containing sodium chloride may be recycled for use as a reactant in a chlor-alkali electrolytic cell. The organic phase containing organic hypochlorite may be used as a chlorinating agent or may be treated with an acid, such as hydrochloric acid, to reclaim free chlorine.

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: The recovery of a magnesium carbonate of high purity from an aqueous slurry comprising a mixture of calcium carbonate and hydrated magnesium carbonate is disclosed. Carbon dioxide is introduced into the slurry while the temperature thereof is maintained not higher than about 40.degree. C. to produce an appreciable concentration of magnesium cations in the water of the slurry. Introduction of carbon dioxide is discontinued while most of the calcium is present as the carbonate. Solids are then separated from the aqueous solution of magnesium cations which is produced. Also disclosed is the removal, e.g., by means of a vacuum pump, of carbon dioxide from the aqueous solution of magnesium cations to precipitate magnesium carbonate and the separation of precipitated magnesium carbonate from the aqueous phase.

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: Magnesium-bearing phosphate rock in small grain size is converted into phosphoric acid so that no by-products, which are difficult to dispose of are produced. The crushed rock is mixed with water and subsequently acidified with nitric acid, the reaction product being filtered and washed before the neutralization point is reached. The wet and filtered rock is treated with nitric acid to form phosphoric acid and a slurry of calcium nitrate tetrahydrate. The previously formed filtrate is mixed with the calcium nitrate tetrahydrate slurry and this mixture is reacted with ammonia and carbonic acid to form ammonium nitrate, magnesium carbonate and calcium carbonate, which are then separated into an ammonium nitrate solution and a mixture of magnesium and calcium carbonates.

Abstract: Magnesia is recovered from scrap lining material rich in magnesia by leach treatment of the material with water in the presence of carbon dioxide under pressure, separating the leaching solution from solid leaching residues, precipitating out magnesium hydrocarbonates from the leaching solution and calcining the precipitate to form magnesia. To make the scrap lining material more readily leachable and enable the production of a rich leaching solution said lining material, prior to the leaching treatment, is treated with steam at a temperature within the range of 100 - 300.degree. C. and corresponding saturation pressures for a period of 1 - 50 hours.