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WO2001085412A2 - Procede de preparation de gypse a purete elevee - Google Patents

Procede de preparation de gypse a purete elevee Download PDF

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Publication number
WO2001085412A2
WO2001085412A2 PCT/JP2001/003910 JP0103910W WO0185412A2 WO 2001085412 A2 WO2001085412 A2 WO 2001085412A2 JP 0103910 W JP0103910 W JP 0103910W WO 0185412 A2 WO0185412 A2 WO 0185412A2
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WO
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Prior art keywords
gypsum
water phase
crystals
calcium
acid
Prior art date
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Ceased
Application number
PCT/JP2001/003910
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English (en)
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WO2001085412A3 (fr
Inventor
Tokumi Mochiyama
Masato Yamaguchi
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Yoshino Gypsum Co Ltd
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Yoshino Gypsum Co Ltd
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Publication of WO2001085412A2 publication Critical patent/WO2001085412A2/fr
Publication of WO2001085412A3 publication Critical patent/WO2001085412A3/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C01F11/468—Purification of calcium sulfates
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B11/00—Calcium sulfate cements
    • C04B11/26—Calcium sulfate cements strating from chemical gypsum; starting from phosphogypsum or from waste, e.g. purification products of smoke
    • C04B11/266—Chemical gypsum
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/46—Sulfates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/20—Particle morphology extending in two dimensions, e.g. plate-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/40—Particle morphology extending in three dimensions prism-like
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/54—Particles characterised by their aspect ratio, i.e. the ratio of sizes in the longest to the shortest dimension
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/10—Solid density
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/80—Compositional purity

Definitions

  • This invention relates to a process for the production of high-purity gypsum which does not contain much impurities. More specifically, the present invention is concerned with a process for producing high-quality gypsum having low impurity content and high whiteness, especially crystals of dihydrate gypsum by having a calcium source such as limestone sufficiently dissolved as a calcium salt with a mineral acid in a water phase, removing impurities in the calcium source as undissolved residue, and then reacting the calcium salt with sulfuric acid to form and crystallize gypsum.
  • a calcium source such as limestone sufficiently dissolved as a calcium salt with a mineral acid in a water phase
  • Gypsum is widely used not only as building materials but also in a variety of fields. In each application field, gypsum is obviously required to have quality and properties specific to the application field. Especially in the fields of molding materials and dental applications, gypsum is not acceptable if it contains impurities and presents a brown to dark gray color due to the impurities, and high-purity gypsum having high whiteness is required. In these application fields, gypsum crystals large in particle size and small in aspect ratio are needed because cast gypsum products are required to have high mechanical strength.
  • a calcium source employed as a starting material such as limestone or lime, contains iron, silica, magnesium and the like as impurities and these impurities remain as sparingly soluble reaction products with sulfuric acid, as are in unreacted forms, or in some instances, together with an unreacted portion of the calcium source in the resulting gypsum, thereby rendering the gypsum to have high impurity contents.
  • the gypsum obtained as described above is generally in the form of fine needle-like crystals, and calcined gypsum which is obtained by calcining such gypsum requires mixing water in an increased amount upon its use .
  • a cast product available from a gypsum slurry having a large mixing water content is accompanied by problems in quality such as lowered strength.
  • an object of the present invention is to make it possible to produce gypsum, which has high whiteness and low impurity contents, at low cost even when a calcium source having high impurity contents is used as a starting material .
  • Another object of the present invention is to provide gypsum large in crystal size and small in aspect ratio, especially crystals of dihydrate gypsum.
  • the present invention provides a process for the production of high-purity gypsum, which comprises reacting a calcium source, as a starting material, with a mineral acid in a water phase to have the calcium source sufficiently dissolved as a calcium salt in the water phase, separating and removing undissolved residue from a resulting water phase, adding sulfuric acid to a water phase, which has been obtained by the removal of the undissolved residue, to crystallize gypsum, and separating the crystallized gypsum from the water phase.
  • FIG. 1 is a flow sheet showing facilities or a plant suitable for use in the practice of the process of the present invention for the production of gypsum.
  • Calcium sources usable in the present invention are commonly known, and include a wide variety of calcium compounds which are available from natural minerals or are produced industrially. Specific examples of such calcium compounds can include natural calcium carbonate sources such as limestone, marble, calcite and aragonite; slaked lime; quick lime; and light calcium carbonate in various crystalline forms, which can be industrially obtained by injecting carbon dioxide gas into a milk of lime. In the present invention, these calcium carbonate sources can be used either singly or in combination. No particular limitation is imposed on the particle size of the calcium source. Calcium sources in a wide range of particle sizes, ranging from fine powder to particles, can each be used as a starting material in the present invention.
  • the present invention has a merit in that the cost of the starting material for gypsum to be obtained can be lowered, as a low-purity calcium compound with silica, iron, aluminum and the like contained as impurities in substantial amounts can be used as a starting material.
  • these calcium sources have properties such that they have low solubility in water but are readily soluble in a mineral acid, such as hydrochloric acid or nitric acid, to form solutions of water-soluble calcium salts.
  • a mineral acid for the dissolution of the calcium source exemplified as described above.
  • a mineral acid one having high purity is not needed but one of general industrial grade is sufficient.
  • waste mineral acids which occur in various chemical industry and semiconductor industry can also be used suitably. No particular limitation is imposed on the mineral acid to be used in the present invention, and its concentration can be determined in relation to a production size at the stage of designing of a plant or facilities for the practice of the present invention.
  • the flow rate of the mineral acid can be controlled by an unillustrated flow meter or solenoid valve arranged in a feed line of the mineral acid in a plant such as that shown in FIG. 1.
  • a mineral acid may be temporarily stored in a reservoir 4.
  • sulfuric acid is suitable.
  • concentration of sulfuric acid and desired one of sulfuric acids the concentrations of which vary widely can be used in view of various factors such as the kinds and contents of impurities in the starting material and the residence time of a water phase in crystallization of gypsum to be described subsequently herein.
  • high-purity gypsum can be produced by the above-described facilities or plant no matter whether the operation is batchwise or continuous. The operation mode of above-described facilities or plant can be freely determined in view of the application field, required quality and economy of the high-purity gypsum available from the present invention.
  • the concentration of the calcium carbonate in the slurry 1 can be set as desired in view of the operation conditions and controllability of the plant.
  • the reaction between calcium carbonate and hydrochloric acid m the dissolver tank 3 can be expressed by the following chemical reaction formula:
  • the pH of the water phase m the dissolver tank 3 may preferably be in a range of from 2 to 6, with a range of 3 to 5 being desired. At a pH lower than this range, the dissolving reaction of calcium carbonate is promoted, leading to an improvement m the yield of crystals of dihydrate gypsum as a final product. On the other hand, however, impurities such as iron are allowed to dissolve m the water phase, eventually resulting in colored crystals of dihydrate gypsum with lowered purity and insufficient crystal growth.
  • the impurities can be removed, but the dissolving reaction of calcium carbonate is retarded, calcium carbonate remains in the unreacted form, and as a result, the calcium carbonate is required in a greater amount for the formation of dihydrate gypsum.
  • the reaction and residence time of the reaction mixture in the dissolver tank 3 and the specification of the apparatus can be determined depending on the kind and particle size of calcium carbonate to be employed, the pH of the water phase during the reaction, the production capacity of the facilities or plant crystals for dihydrate gypsum, and the like.
  • the dissolver tank 3 may preferably be constructed of a material having corrosion resistance to hydrochloric acid and calcium carbonate used in the above-described reaction. It is also desired to arrange an agitator 5 in the tank such that the contents can be stirred evenly. No particular limitation is imposed on the specification of the agitator 5, and any agitator can be used insofar as it is generally employed.
  • the flow rate of the slurry and/or hydrochloric acid can be controlled depending on the liquid level of the water phase in the dissolver tank 3 or the pH of the water phase in the dissolver tank 3 by an unillustrated solenoid valve of flow meter arranged in the feed line from the slurry reservoir 2 and/or hydrochloric acid tank 4 to the dissolver tank 3.
  • an unillustrated solenoid valve of flow meter arranged in the feed line from the slurry reservoir 2 and/or hydrochloric acid tank 4 to the dissolver tank 3.
  • carbon dioxide gas 6 is produced. It is necessary to safely exhaust this gas out of the system by an unillustrated exhauster.
  • the water phase which has been drawn out of the dissolver tank 3 and contains calcium chloride, is filtered by a solid-liquid separation means 7 such as a filter, whereby undissolved residue 8 contained in he water phase, such as iron and silica, is separate and removed.
  • the residue 8 so separated and removed is discharged as sludge out of the system, and the water phase is fed to the subsequent step.
  • this solid-liquid separation means 7 it is desired to adopt an appropriate apparatus or plant out of general centrifugal, pressure or vacuum filters in view of the purity of the starting material, the amount of the undissolved residue, the speed of the treatment, the residence time of the water phase in the dissolver tank 3, and so on.
  • the water phase from the above-described solid-liquid separation means 7 is fed to a crystallization tank 9, in which crystals of dihydrate gypsum are formed.
  • a crystallization tank 9 in which crystals of dihydrate gypsum are formed.
  • the reaction temperature between calcium chloride and sulfuric acid 10 in the water phase is set as high as possible.
  • the temperature of the water phase may preferably be set in a range of from 30 to 80°C, with a temperature range of from 40 to 75°C being desired. If the temperature is set higher beyond the above range, anhydrous gypsum is crystallized. At a temperature lower than the above range, on the other hand, the growth of crystals of dihydrate gypsum becomes slower.
  • an unillustrated flow meter and solenoid valve can also be arranged for the control of the process in the feed line between the equalizing tank 11, which is provided with the heating means 12, and the crystallization tank 9 such that the flow rate of the water phase with calcium chloride contained therein can be controlled.
  • sulfuric acid 10 is desired as a supply source for sulfate ions as described above. Its concentration can be chosen as desired depending on the specification of the apparatus.
  • a reaction in which crystals of dihydrate gypsum are formed upon addition of the sulfuric acid 10 to the heated water phase can be expressed by the following chemical reaction formula :
  • Gypsum is available primarily in three crystalline forms, that is, dihydrate, hemihydrate and anhydrite. Especially in the crystallizing reaction of gypsum in such a solution as described above, each crystalline form has its own stable region depending on salts concurrently contained in the water phase and the temperature condition of the water phase. To stably crystallize crystals of dihydrate gypsum, it is therefore necessary to maintain the concentrations of the above-described salts and the temperature condition of the water phase within stable regions for crystals of dihydrate gypsum.
  • the reaction temperature of the water phase and the concentrations of coexisting chlorine ions in the water phase for the formation of the crystals of dihydrate gypsum may desirably be maintained in the following ranges from the standpoint of the formation and growth of crystals of dihydrate gypsum in the crystallization tank 9.
  • reaction temperature high as described above.
  • the higher the reaction temperature the greater the solubility of the formed crystals of dihydrate gypsum in the water phase and hence, the lower the yield of crystals of dihydrate gypsum. It is therefore desired to set the reaction temperature at a high temperature within a range in which resulting crystals of dihydrate gypsum are allowed to grow while retaining the form of dihydrate.
  • reaction temperature in the crystallizing tank 9 within a range of from 30 to 80°C, preferably within a range of from 40 to 75 and further, to control the total concentration of chlorine ions in the water phase at 5 to 15 wt.%. If the reaction temperature or the total chlorine ion concentration is maintained high beyond the above-described temperature or concentration range, the water phase is a stable region for andhydrous gypsum, so that anhydrous gypsum is allowed to crystallize and further, is hardly allowed to remain as dihydrate during crystal growth.
  • reaction temperature of the total chlorine ion concentration is set lower than the above-described range, fine needle-like crystals of dihydrate gypsum are formed, crystals of dihydrate gypsum can hardly be obtained with desired size and shape even if the residence time is set long.
  • the residence time of the water phase in the crystallizing tank 9 is set longer under the above- described conditions, thick crystals of dihydrate gypsum are obtained with an increased particle size. It is, therefore, preferred to hold the water phase for about 0.5 to 12 hours or so in the crystallizing tank 9. Crystals of dihydrate gypsum are, for example, in a fine needle-like form with an aspect ration of from 10 to 20.
  • the residence time By setting the residence time at several hours or so, coarse (plate-like or short prism-like) crystals having, for example, a thickness of approx. 100 ⁇ m in minor axis diameter can be obtained. Accordingly, the residence time should be determined in view of the application and required quality of crystals of dihydrate gypsum to be obtained.
  • the concentration of solids (crystals of dihydrate gypsum) in the crystallizing tank 3 may preferably be in a range of from 5 to 30 wt.%, with a range of from 10 to 25 wt.% being desired.
  • a solid concentration lower than 5 wt . % cannot form crystals of dihydrate gypsum in a large amount in a single cycle of step, and is disadvantageous from the standpoint of production cost.
  • a solid concentration higher than 30 wt.% leads to a reduction in the below-described washability of the crystals with water and hence to inclusion of more impurities in crystals of gypsum to be obtained eventually. Solid concentrations outside the above range are, therefore, not preferred.
  • the crystals of dihydrate gypsum formed in the crystallizing tank 9 are in a fine needle-like form in the beginning of the crystallizing reaction, and in the course of the subsequent crystal growth, the setting of a long residence time in the crystallizing tank 9 makes it possible to obtain thick crystals of dihydrate gypsum.
  • a known habit modifier 18 or a crystal habit regulator can be added concurrently with sulfuric acid to the crystallizing tank 9.
  • Such a habit modifier can include organic carboxylic acids, such as citric acid, aleic acid, succinic acid and sulfosuccinic acid, and salts thereof; water-soluble alkali metal salts of fatty acids such as palmitic acid, linoleic acid, ricinolic acid and glycoholic acid; and alkylsulfonate salts, alkylbenzenesulfonate salts, and salts of the sulfate esters of higher alcohols. Particularly preferred are alkali metal dodecylbenzenesulfonates, especially, the sodium salt.
  • organic carboxylic acids such as citric acid, aleic acid, succinic acid and sulfosuccinic acid, and salts thereof
  • water-soluble alkali metal salts of fatty acids such as palmitic acid, linoleic acid, ricinolic acid and glycoholic acid
  • Whichever habit modifier is used its amount can be set at about 5,000 ppm or lower based on the water phase although its effects on the growth of crystals of dihydrate gypsum vary from one habit modifier to another.
  • sodium dodecyl- benzenesulfonate when sodium dodecyl- benzenesulfonate is used as a habit modifier, it can be added to at a concentration of about 500 ppm or lower, desirably from 5 to 100 ppm, more desirably from 5 to 50 ppm based on the water phase. Addition of sodium dodecylbenzenesulfonate at a concentration higher than the above range is not observed to bring about any additional effect on the growth of resulting crystals of dihydrate gypsum, because its habit-modifying effect is saturated.
  • Such a habit modifier makes it possible to obtain plate-like or short prism-like crystals of dihydrate gypsum having an aspect ratio of from 2 to 4. Insofar as crystals of dihydrate gypsum can be formed, it is necessary to promote the growth of crystals under high temperature conditions. Use of such high temperature condition, on the other hand, is accompanied by a problem in that due to an increase in the solubility of the crystals in the water phase, the yield of crystals of dihydrate gypsum may be lowered.
  • the crystallizing tank in the form of two or more tanks, to connect these crystallizing tanks in series, to draw a water phase with the formed crystals of dihydrate gypsum therein out of the first crystallizing tank, to feed the water phase to the second and subsequent crystallizing tanks, and then to hold the water phase under stirring in the tanks to subject the crystals to aging.
  • FIG.1 illustrates a case in which two crystallizing tanks 9,9' are connected in series. Differentiation in temperature between a water phase in the second crystallizing tank (aging tank) 9' and a water phase in the first crystallizing tank 9 within the above-described temperature range of the water phase makes it possible to achieve an improvement in the yield of crystals of dihydrate gypsum. Described specifically, the dissolution of dihydrate gypsum in the water phase can be minimized by crystallizing dihydrate gypsum under a high water phase temperature condition in the first crystallizing tank 9 and setting the temperature of the water phase in the subsequent aging tank 9' lower than the above-mentioned temperature to lower the solubility of dihydrate gypsum.
  • the aqueous solution of calcium chloride and the sulfuric acid can be fed all together to the first crystallizing tank 9 or can be fed in portions to the individual tanks 9, 9' .
  • the single or two or more crystallizing tanks 9,9' should not permit precipitation of coarse crystals of formed dihydrate gypsum and should assure prompt spreading of sulfuric acid into the water phase .
  • crystallizing tanks 9,9' each of which is internally provided with a stirring blade 5 and radial baffles or draft tubes can be suitably employed.
  • the tanks 9, 9' and the like may be constructed preferably with a material having corrosion resistance to hydrochloric acid.
  • an unillustrated diluting tank can be arranged additionally. It is also desired to arrange an unillustrated solenoid valve and flow meter, which have acid resistance, in the feed line of sulfuric acid and to control the flow rate of sulfuric acid.
  • the water phase which contains crystals of dihydrate gypsum aged as a result of the holding of the water phase as described above, is subjected to solid-liquid separation in a solid-liquid separator 13 such as a filter, whereby crystals 14 of dihydrate gypsum are separated and collected.
  • a solid-liquid separator 13 such as a filter
  • crystals 14 of dihydrate gypsum are separated and collected.
  • thickened or plate-like or short prism-like crystals of dihydrate gypsum can be more easily collected by filtration.
  • the filtered crystals of dihydrate gypsum are washed with washing water 15 and/or are regulated in pH (not shown) and are then dried, whereby the crystals 14 of dihydrate gypsum are obtained in a desired form.
  • the washing effluent can be discharged out of the system through a suitable line 17 or can be returned to the dissolver tank 3.
  • the content of chlorine contained in the dihydrate gypsum can be lowered to 50 ppm or less.
  • this washing can be performed in a manner known per se in the art, for example, by spraying.
  • the above-described pH regulation can be conducted by washing the crystals of dihydrate gypsum with an aqueous alkaline solution such as an aqueous solution of lime or by mixing the crystals of dihydrate gypsum again with water into slurry and washing the slurry with an aqueous solution of lime or a like solution.
  • an aqueous alkaline solution such as an aqueous solution of lime
  • a water phase (mother liquor) 16 which has been separated by the solid-liquid separation, is an aqueous solution of hydrochloric acid.
  • the amount of hydrochloric acid to be replenished newly to the dissolver tank 3 is as little as about 20 wt.% of the mother liquor (aqueous solution of hydrochloric acid) 16 recirculated for reuse, thereby making it possible to achieve a reduction in the cost for the raw materials.
  • the solid-liquid separator 13 in this step any known solid-liquid separator, for example, a filter can be used in practice although use of a solid-liquid separator having acid resistance is preferred.
  • calcium carbonate and hydrochloric acid were used as preferred examples . It is, however, to be noted that the present invention can also bring about similar results even when a calcium source other than calcium carbonate and a mineral acid other than hydrochloric acid are used.
  • Example 1 As a starting material, low-purity limestone powder was used. The followings are the results of its chemical analysis: CaC0 3 97.0 wt.%
  • the above-described limestone powder (618 g) was mixed and agitated with an equiamount of water into a 50 wt.% slurry, whereby a slurry of the limestone powder was obtained.
  • the slurry was next poured together with hydrochloric acid (2,650 g) , the concentration of which was 15 wt.%, into the dissolver tank 3.
  • the limestone powder was dissolved in the hydrochloric acid so that a solution of calcium chloride was obtained.
  • Carbon dioxide gas 6 which was produced in the course of the dissolution was exhausted out of the system by a local exhauster.
  • the solution of calcium chloride was filtered by a line filter 7 to separate and remove undissolved residue 8, and the water phase was temporarily transferred to the equalizing tank 11 provided with the heating means 12.
  • the dry weight of the undissolved residue 8 was 26 g.
  • the water phase in the tank 11 was then directly heated by steam injection such that its temperature was raised to 75°C.
  • the water phase was then fed to the crystallization tank 9.
  • sodium dodecylbenzenesulfonate was added such that its content reached about 35 ppm based on the amount of the liquid in the crystallization tank 9.
  • sulfuric acid 8 the concentration of which was 80 wt.% was also added such that its contents became approximately equal in equivalent to calcium ions in the water phase, followed by a reaction under stirring for 6 hours.
  • the liquid temperature was then lowered to 65°C, at which crystals of dihydrate gypsum were subjected to aging while holding the water phase there for 6 hours under stirring.
  • the concentration of chlorine ions in the water phase during the aging was 10 wt.%.
  • the water phase with crystals of dihydrate gypsum contained therein was then filtered by filtration at the water-liquid separator 13, the crystals were washed with an equiamount of water, and the crystals of dihydrate gypsum were obtained. Properties of the crystals of dihydrate gypsum obtained after drying were investigated. The results are shown below.
  • Example 1 A similar test was conducted by using the mother liquor 16, which had been recovered as described above, likewise the hydrochloric acid employed in Example 1. Limestone powder in the same amount as in Example 1 was similarly formed into a slurry, After the aqueous solution of hydrochloric acid (mother liquor) obtained m Example 1 was added to the slurry such that the aqueous solution of hydrochloric acid amounted to 20 wt.% of the weight of the slurry, the concentration of the slurry was adjusted to the same level as in Example 1, and a test was then conducted as in Example 1. As a result, the resultant crystals of dihydrate gypsum showed similar properties as in Example 1. Further, calcined gypsum obtained subsequent to calcination also had similar physical properties as the calcined gypsum obtained in Example 1. Example 3
  • Example 2 Further, the procedures of Example 2 were repeated 4 times additionally, that is, were repeated 5 time in total.
  • the resultant crystals of dihydrate gypsum were tested as in Example 1.
  • the crystals of dihydrate gypsum showed similar properties as in Example 1.
  • calcined gypsum obtained subsequent to calcination also had similar physical properties as the calcined gypsum obtained in Example 1.
  • plate-like or short prism-like crystals of dihydrate gypsum of high purity, high whiteness, large bulk density and small aspect ratio can be efficiently obtained even when a low-purity calcium source is used. Calcination of such crystals of dihydrate gypsum can also provide calcined gypsum of high purity, which is satisfactory in spray mixing water amount, setting time, and physical properties such as tensile strength.

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Abstract

L"invention concerne un procédé de préparation de gypse à pureté élevée consistant à faire réagir une source de calcium avec un acide minéral en phase aqueuse de manière obtenir une source de calcium suffisamment dissoute sous forme d"un sel calcium dans la phase aqueuse, à séparer et éliminer des résidus non dissous de la phase aqueuse obtenue, à ajouter de l"acide sulfurique à une phase aqueuse, qui a été obtenue par élimination des résidus non dissous, au gypse cristallisé, et à séparer ce dernier de la phase aqueuse. Selon le procédé, des cristaux du type à plaquettes ou du type prismatique court de gypse déshydraté à pureté élevée, à blancheur élevée, à densité de matière première importante et à allongement court peuvent être obtenus de façon efficace même quand on utilise une source de calcium à pureté faible. En calcinant de tels cristaux de gypse déshydratés, on peut obtenir un gypse calciné à haute pureté, qui donne satisfaction concernant la quantité d"eau destinée à un mélange de pulvérisation, le temps de prise et les propriétés physiques telles que la résistance à la traction.
PCT/JP2001/003910 2000-05-12 2001-05-10 Procede de preparation de gypse a purete elevee Ceased WO2001085412A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2000-140624 2000-05-12
JP2000140624 2000-05-12

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WO2001085412A2 true WO2001085412A2 (fr) 2001-11-15
WO2001085412A3 WO2001085412A3 (fr) 2002-08-22

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KR (1) KR20010104238A (fr)
CN (1) CN1323742A (fr)
AU (1) AU4381501A (fr)
SG (1) SG86468A1 (fr)
WO (1) WO2001085412A2 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2009277498B2 (en) * 2008-07-31 2012-07-12 Yoshino Gypsum Co., Ltd. Process for continuous modification of dihydrate gypsum and modified dihydrate gypsum obtained by the process
JP2014128744A (ja) * 2012-12-27 2014-07-10 Mitsuboshi Mining Co Ltd 水洗スラッジの処理方法
CN107572571A (zh) * 2017-10-19 2018-01-12 湖北民族学院 高强度片状α‑半水石膏的制备方法
EP3245159A4 (fr) * 2015-01-14 2018-10-03 Imerys USA, Inc. Procédé de conversion de carbonate de calcium naturel en carbonate de calcium précipité
CN118851697A (zh) * 2024-07-04 2024-10-29 新洋丰农业科技股份有限公司 一种盐碱地排水管及其制备方法与应用

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AU2009277498B2 (en) * 2008-07-31 2012-07-12 Yoshino Gypsum Co., Ltd. Process for continuous modification of dihydrate gypsum and modified dihydrate gypsum obtained by the process
JP2014128744A (ja) * 2012-12-27 2014-07-10 Mitsuboshi Mining Co Ltd 水洗スラッジの処理方法
EP3245159A4 (fr) * 2015-01-14 2018-10-03 Imerys USA, Inc. Procédé de conversion de carbonate de calcium naturel en carbonate de calcium précipité
EP3245159B1 (fr) 2015-01-14 2021-06-02 Imerys USA, Inc. Procédé de conversion de carbonate de calcium naturel en carbonate de calcium précipité
CN107572571A (zh) * 2017-10-19 2018-01-12 湖北民族学院 高强度片状α‑半水石膏的制备方法
CN107572571B (zh) * 2017-10-19 2019-04-09 湖北民族学院 高强度片状α-半水石膏的制备方法
CN118851697A (zh) * 2024-07-04 2024-10-29 新洋丰农业科技股份有限公司 一种盐碱地排水管及其制备方法与应用

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CN1323742A (zh) 2001-11-28
WO2001085412A3 (fr) 2002-08-22

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