Showing papers on "Gypsum published in 1980"

The Chemistry of the Reclamation of Sodic Soils with Gypsum and Lime

Abstract: Sodic soil reclamation was theoretically evaluated assuming equilibrium chemistry and piston movement of soil solution. The effective solubility of gypsum when mixed with a sodic soil is increased because the exchange phase acts as a sink for Ca²⁺ until both the gypsum dissolution and exchange reactions reach equilibrium. The electrical conductivity of a soil solution in equilibrium with both gypsum and an exchangeable sodium fraction (ENₐ) of 0.0 and 0.43 is 2.3 and 14 dS m⁻¹. Thus, mixing gypsum into the soil hastens reclamation and provides higher solution concentrations for the maintenance or improvement of the soil hydraulic conductivity. The amount of gypsum dissolved, expressed in moles of charge (equivalents), is a linear function of the moles of exchangeable Na⁺ replaced; r² values typically exceeded 0.98. The slope of the regression line decreased with increasing final ENₐ. Typical values were 1.40, 1.27, and 1.20 moles of charge gypsum dissolved per mole of exchangeable sodium replaced at final ENₐ's of 0.05, 0.10, and 0.15. The inclusion of lime equilibrium reduces these slopes by 3, 6, and 9% for PCO₂'s of 1, 4, and 10 kPa (1, 4, and 10% CO₂). Gypsum requirements for calcareous, sodic soils based on quantitative replacement of exchangeable sodium should be increased by factors of 1.3 to 1.1 depending on the desired final levels of exchangeable sodium.

Design of foundations of dams containing soluble rocks and soils

Abstract: Summary Four major classes of soluble rocks or soils have been found on dam sites. They are represented by the minerals gypsum, anhydrite, calcium carbonate and halite. Dissolution of these materials can constitute a risk in terms of potential settlements and leakage paths within the foundations of dams. Engineering solutions depend on the solubility and specific rate of solution of the minerals; also upon hydraulic conditions imposed on the foundations. This paper demonstrates a quantitative basis for the design of safe structures which contain these soluble minerals within their foundations. Site investigation procedures are described so that potential estimates of relevant ground parameters may be obtained and used in engineering design.

Dolomite is an Evaporite Mineral Evidence from the Rock Record and from Sea-Marginal Ponds of the Red Sea

Abstract: Despite recent suggestions to consider dolomite a product involving freshwater especially the reaction between freshwater and seawater more recent work in the rock record and in sea marginal ponds of the Red Sea indicates that dolomite is an evaporite mineral and that most dolomites owe their origin to hypersaline brines Although dolomite may form under a variety of depositional conditions including freshwater soils caliche or deep sea most dolomites in the rock record formed under conditions of hypersalinity A close lateral vertical or temporal relationship commonly exists between dolomite and evaporite deposits although this relationship is not universal nor everywhere demonstrable In most situations in which evaporites fail to accompany dolomite original evaporites have commonly been removed following their precipitation However the imprint of evaporite minerals and other evidence for hypersalinity may be preserved Evidence for vanished evaporites has been inferred from mineralogic sedimentary and biotic characteristics including pseudomorphs after sulfate nodules pseudomorphs after halite euhedral quartz crystals quartzine and lutecine saddle shaped dolomite crystals authigenic potassium feldspar solution collapse breccias abundance of ooids half moon ooids presence of stromatolites and paucity of fauna In places evaporite minerals have been preserved as small inclusions Research in modern sea marginal ponds of the Red Sea shows that dolomite forms only where gypsum andlor anhydrite is also present Among submerged algal mats where gypsum is absent the carbonate minerals are aragonite or high magnesian calcite by contrast where gypsum is abundant in deeper parts of ponds or among submerged algal mats dolomite is present Likewise in a pond marginal sabkha not only halite gypsum and anhydrite but also dolomite form a cement between constituent particles The high salinities at which gypsum precipitates up to 330 X 103 mgll in the summer and the observation that dolomite prefers sulfate association suggest that both minerals owe their origin to hypersaline brines Fresh or brackish waters are unavailable in these ponds the waters are hypersaline at all times Dolomite almost by defmition must be considered an evaporite mineral in these hypersaline ponds

Process of producing a building product of gypsum, particularly a gypsum slab

Abstract: This invention provides a process of producing a building product, particularly a gypsum slab having preferably a density of below 800 kg/m3, with gypsum and mixing water. The quantity of mixing water required for rehydration and molding is at least substantially completely introduced into the gypsum by means of water saturated porous particles added in a distributed form. The process comprises the steps of intimately mixing water saturated particles with pulverous gypsum to form a fluid mixture; converting said fluid mixture at least almost completely without the application of pressure to the shape of a gypsum building product; permitting mixing water of the water saturated particles to be absorbed by the pulverous gypsum, and permitting the resulting mixture to set and harden.

High density interface gypsum board and method for making same

Abstract: A gypsum wallboard, and the method of manufacture, wherein a defoamer is disposed at the gypsum-paper interface during manufacture, causing the foam, present in the core forming gypsum slurry, to break down at the gypsum-paper interface, increasing substantially the density of the gypsum at the interface, relative to the density throughout the center portion of the gypsum core

Sag-resistant gypsum board containing coal fly ash and method for making same

Abstract: A gypsum board consisting essentially of a monolithic cellular core of set gypsum and a fiberous cover sheet encasement provided with improved properties by the gypsum core having incorporated therein coal fly ash in an amount of about 1-20% by weight of stucco in the gypsum slurry used in forming the board and method of producing the board are disclosed.

Waterproof gypsum molded product

Abstract: The present invention provides a gypsum molded product having excellent waterproof properties without impaired strength by adding alkaline metal alkylsiliconates or phenylsiliconates together with calcium hydroxide or calcium oxide to gypsum; poly(α,β-unsaturated carboxylic acid) may be used in combination with the above, if desired. According to the present invention, the preparation of a gypsum molded product, particularly a gypsum from desulfurization of exhaust gas, is contemplated.

Plant-controlled supratidal anhydrite from Al-Khiran, Kuwait

Abstract: We report here that in the supratidal zone of the Al-Khiran sabkha, diagenetic anhydrite occurs exclusively in association with the living halophyte Halocnemum strobilaceum (Pallas) M .B. This anhydrite has a hair cream-like consistency and the bulk of it has formed as pseudomorphs after gypsum crystals. On the death of the plant at the end of its life cycle, the anhydrite is hydrated back to gypsum. This two-way transformation results in a series of characteristic textures, whose preservation could be due to the comparative ‘youth’ of the sabkha, which is in the very earliest stages of evaporite diagenesis.

Experimental growth of primary anhydrite at low temperatures and water salinities

Abstract: Well-crystallized anhydrite nucleates and grows readily at temperatures and salinities resembling those in hot, arid regions, provided that certain types of macromolecular organic compounds are also present. In experiments utilizing two different crystal-growth techniques at 60 °C and 50‰ NaCl, small amounts of polymaleic acid, polyacrylic acid, and a phosphate ester induced crystallization of well-formed anhydrite laths 0.5 to 2 μm in size. This anhydrite apparently precipitated through primary nucleation rather than through secondary nucleation in the presence of gypsum or bassanite precursors.

Some hydration investigations involving portland cement - effect of calcium carbonate substitution of gypsum

Abstract: The effects of partially and fully replacing gypsum by limestone in portland cement under a variety of conditions have been examined. Different grinding temperatures and two different base gypsum levels have been investigated to assess the effects on setting and compressive strength development. Examination of early hydration up to two hours was carried out in order to elucidate the mechanism of chemical reaction in the presence of limestone and to compare this with reaction in the presence of gypsum. The results showed that some substitution of gypsum by limestone is possible without deleteriously affecting setting behaviour and compressive strength development from three days to one year. (Author/TRRL)

Influence of Size of Gypsum Particles on the Hydraulic Conductivity of Soils

Abstract: Column studies with two soils showed that hydraulic conductivity decreased with the addition of gypsum of particle size less than 44 micrometers but was unaffected by a particle size of 0.25 to 1.00 millimeter in diameter. The effect of lime powder on the initial hydraulic conductivity of the soils was similar to that of gypsum. During leaching, however, the hydraulic conductivity with gypsum addition increased, whereas the hydraulic conductivity with lime addition remained low. These results suggest that the reduction in hydraulic conductivity of soils that contain gypsum is due mainly to mechanical plugging by the small gypsum particles.

Lump process alpha gypsum

Abstract: An improved "lump" process for producing alpha gypsum, calcium sulfate hemihydrate, from natural gypsum rock of the type wherein lumps of gypsum rock particles (a minimum of about 1/2 inch or 1.3 cm. in size) are calcined to low water-demand alpha hemihydrate by autoclaving in a saturated steam atmosphere, quickly dried and pulverized is disclosed. The improvement allows the thorough processing of natural gypsum as large sized particles or containing considerable selenite and includes the steps of initiating calcination without crystal habit modifier and, after hemihydrate formation has commenced, adding crystal habit modifier and completing calcination under increased steam pressure.

Production of 22type anhydrous gypsum

Abstract: PURPOSE:To obtain high density II-type anhydrous gypsum providing a water- added hardened body of high compressive strength by adding a predetermined amt of a habit modifier to an above 20wt% flurry of gypsum sollowed by pressure hydrothermal treatment at a predetermined temp without agittaing CONSTITUTION:0005-10wt% of a known habit modifier such as succinic acid is added to an above 20wt% slurry of gypsum and subjected to pressure hydrothermal treatment at above 170 degC for above about 3 hr without agitating, thus obtaining II-type anhydrous gypsum with considerably enhanced properties such as a bulk density above 1, a water carrying capacity below 40% and a compressive strength of a hardened body above 100kg/cm Conditions outside the above ranges result in low bulk density of gypsum and low mechanical strength of a hardened body

Method of and apparatus for the treatment of pyrite-containing mineral coal

Abstract: A method of and an apparatus for the treatment of mineral coal containing pyrite wherein the mined mineral product is milled, classified into a fine component and a coarse component, the coarse component is recycled and the coarse component in whole and in part is subjected to density suspension so that a light product consisting predominantly of coal is separated from a heavy product comprising the pyrite and mineral detritus. This latter product forms a combustible mixture which is subjected to fluidized bed combustion in the presence of lime to produce an exhaust gas which is used to fluidize the vibrating trough serving as the density separator and as the drying gas and entrainment gas for the mill. The solid residue consists of gypsum (calcium sulfate) and ash and can be used, e.g. in the mixture of cement or plastic, but in any event does not pose an environmental hazard.

Dental compositions of improved properties

Abstract: A dental gypsum composition having good pourable consistency and controlled mixing and setting characteristics comprising a mixture of calcium sulfate hemihydrate (calcined gypsum), a condensation product of formaldehyde with a cyclic hydrocarbon containing sulfonic acid groups, and magnesium aluminum silicate When dispersed in water and cured, this composition provides set products having improved hardness and strength properties

Production of gypsum

Abstract: PURPOSE:To efficiently produce spherical gypsum made of fibrous gypsum in simple operation by adding powder of inorg. substance such as talc when gypsum, hemihydrate gypsum or sol. anhydrous gypsum is slurried and subjected to hydrothermal reaction. CONSTITUTION:Gypsum, hemihydrate gypsum or sol. anhydrous gypsum is added to water or an aq. soln. contg. inorg. acid, org. acid or water sol. org. substance such as ethylene glycol, and below 10mu powder of inorg. substance such as talc, silicic acid, silicic anhydride or CaCO3 is further added in an amt. of 0.001-30% to the amt. of the raw material gypsum to slurry the gypsum. This slurry is then subjected to hydrothermal reaction at 100-180, pref. 105-140 deg.C usually under press. with agitating for 1-90min. The resulting spherical gypsum has a uniform diameter and low bulk density, and it is used as building materials such as a panel, insulating material and heartwood, a filler for plastics, an adsorbent, a filter medium, a catalyst, etc.

Amelioration of salt damage to cotoneaster by gypsum.

Abstract: Cotoneasters were grown in a gypsum-treated medium and salinized with 0.15A/ NaCI. Gypsum was applied in 3 forms with 2 application methods and at 2 rates. Controls received no gypsum additions. Control plants were severely injured, while gypsum treated plants showed reduced damage. The incorporated gypsum was more effective in alleviating damage than surface applications. Rate was not a factor as 20 lb/100 sq. ft. proved as effective as 40 lb/100 sq. ft. All 3 gypsum formulations were effective but the granular materials were easier to work with when compared to the fine-ground. Electrical conductivity of the media leachates were significantly lower in incorporated gypsum treatments compared to the control. The pH of the leachates was not affected by gypsum treatments. Salt damage to vegetation along highways, sidewalks and in containers has been well documented (3,5,9,10). Injury (2,5,10) results from aerial and soil-deposited salts. Plants in tree lawns, parkways, planters or close to roadways are more apt to be injured by soil salts (3,9). Damage to containerized plant materials is often accentuated because salt-laden snow is piled around the containers and tree lawn areas. Gypsum has been shown to reduce Na uptake by plants (1) and, possibly Cl (6), and is recommended as an ameliorative treatment for reducing salt injury to Acer saccharum, sugar maple, in New England (9). The possible beneficial effects of gypsum on the alleviation of the soil salt damage to containerized plants have not been critically examined. This study determined the ameliorative effects of 3 gypsum sources, 2 application methods, and 2 rates on the appearance of Skogsholm cotoneaster, and the media electrical conductivity and pH. Materials and Methods Healthy, vigorous rooted cotoneaster cuttings were transplanted into 15cm plastic pots containing a soil:peat:perlite (1:1:1) medium or a gypsum-amended medium of the same composition. Three gypsum sources were used: United States Gypsum Granular; Sof'n-Soil Lawn and Garden (granular); and Sof'n-Soil Lawn and Garden (fine). These sources were incorporated or surface applied at rates of 20 and 40 lb/100 sq. ft. (17.6 g/pot=20 Ib rate or 35.3 g/pot=40 Ib rate). The surface treatment was applied after transplanting, while the incorporated gypsum was mixed with the media and the plants potted thereafter. Control consisted of the medium without gypsum. Plants were pruned to a uniform height and placed in the greenhouse under 15-hour photoperiods at 24° day/20 °C night temperatures. Plants were fertilized for 8 weeks with Hoagland's No. 1 solution (4) at a rate of 200 ml/container on alternate days. Leachates were collected weekly from each container and pH and electrical conductivity were determined. When no significant pH or conductivity changes were evident, the leachates were collected at 2 week intervals thereafter. Only initial and final values are presented. Salt treatments were initiated in the ninth week. Each container was supplied with 200 ml of 0.15/V NaCI on alternate days and with a Hoagland's or deionized water treatment the other days. The experiment was terminated after 4 weeks when the majority of the control plants showed 70 to 80 percent or greater necrosis. Plants were evaluated using a rating index (See Table 1 for criteria). Plants were arranged in a completely randomized design with 5 single plant replicates per treatment. Results and Discussion Gypsum ameliorated the salt damage on cotoneaster in all treatments except the Sof'n-Soil (fine) surface applications (Table 1). Control plants were approximately 70 to 80 percent necrotic while plants grown with the 3 incorporated gypsum sources at the 2 rates were less The senior author is presently Director, UGA Botanical Garden, Athens, GA 30605. Journal of Arboriculture 6(4): April 1980 109 than 40 percent necrotic. A high rate of soil salt application was used in this study to produce toxicity symptoms. Under normal conditions container-grown plants would not be exposed to these quantities and the ameliorative effect of gypsum would possibly be greater. The incorporated gypsum proved more effective than surface applications. The use of gypsum on established plants in tree lawns and containers, however, would probably necessitate surface applications. Three gypsum applications methods used in Maine experiments were most effective in the following order: surface, subsurface, and subsurface combined with mechanical soil aeration (9). Drill hole application would work but the cost might preclude this method. In new plantings the gypsum could be easily mixed with the backfill. Both rates appeared to be effective. The 20 and 40 lb./100 sq. ft. translate into 4.36 and 8.72 tons/acre, respectively. Rates of gypsum application required to achieve soil salts reduction varies from 4 to 15 tons/acre (9). Plice (7) reported that 4 to 6 tons/acre reclaimed strongly saline soils, and that 12 tons/acre offered the advantage of reducing salts more quickly. Gypsum treatments are effective over a long time period and annual or biennial treatments are not necessary. The electrical conductivities (measure of total ions in solution) were significantly lower in all incorporated gypsum treatments than in the controls. Surface applications of Sof'n-Soil (granular) at 40 Ib and Sof'n-Soil (fine) at both rates also resulted in lower conductivities. The plants grew better in the soils with lower salt content. This is to be expected in view of the reported effects of high soil salts on plant growth (8). Although tissue analysis was not completed, it is logical to assume that levels of Na and Cl were lower in plants grown with gypsum. Ayoub (1) reported a 30 to 85 percent reduction in leaf Na from plants grown in saline soils treated with gypsum. Jacobs (6) showed that gypsum applications resulted in greater soil Cl reductions than those of controls (non-gypsum). Both Na and Cl ions have been implicated in plant salt damage (2,5,10) and if they are effectively reduced in plant tissue then increased vigor should result. The pH changes due to gypsum treatments were negligible although there was 0.5 to 0.8 unit change from the initial values to the final. This was Table 1. Effect of gypsum sources, application methods, and rates on the appearance of Cotoneaster dammeri 'Skogsholmen' and on the initial and final leachate electrical conductivities and pH values. Gypsum source Control

Manufacture of type hemihydrate gypsum

Abstract: PURPOSE:To obtain alpha-type hemihydrate gypsum causing no lowering in strength and no efflorescence phenomenon by adding a habit modifier, sodium chloride, calcium chloride and a needlelike hemihydrate gypsum seed to a gypsum slurry followed by heating under atmospheric press. CONSTITUTION:To a gypsum slurry contg. an adequate amt. of a habit modifier are added 2-3 parts by wt. of sodium chloride and 10-18 parts of calcium chloride to 100 parts of water in the slurry. Needlelike himihydrate gypsum of 1-2mu minor axis and 10-30mu major axis is further added as a seed in an amt. of 0.3-1 part to 100 parts of gypsum. The slurry is then heated at the transition temp.-the b.p. under atmospheric press. to obtain prismatic or platelike alpha-type hemihydrate gypsum. The seed may be added in the form of a slurry or powder, yet it is pref. added when the temp. of the gypsum slurry reaches the transition temp.

Modifying method of gypsum formed in preparing phosphoric acid by wet process as by-product

Abstract: PURPOSE: To modify gypsum formed as a by-product so as to be usable in the same manner as the natural gypsum, by treating the gypsum formed as the by-product in the form of an aqueous slurry with a hydrocyclone, separating particles of a given particle size, adding lime thereto, a drying the separated particles CONSTITUTION: Gypsum formed as a by-product in preparing phosphoric acid by the wet process is stirred as an aqueous slurry, and treated with a hydrocyclone and disintegrated Solid particles and soluble impurities finer than the gypsum particles are removed to give the separated particle size of about 5W20μ Lime is then added to the separated gypsum particles to adjust to an alkaline pH of about 8W10 and fix the phosphoric acid content as a water-insoluble calcium salt According to the method, the gypsum formed as a by-product can be modified to gypsum fit for cement without discharging an alkaline waste water COPYRIGHT: (C)1982,JPO&Japio

Manufacture of light weight spherical gypsum

Abstract: PURPOSE:To obtain a light weight spherical gypsum having a homogeneous and fracture-free crystal by the procedure in which gypsum is heated with stirring in an aqueous solvent in the presence of the bubbles of air or N2 introduced CONSTITUTION:A spherical gypsum consisting of fibrous hemihydrate gypsum is manufactured by heating with stirring an aqueous solution of dihydrate (or hemihydrate) gypsum or soluble anhydrous gypsum, containing an acid, eg, acetic acid, hydrochloric acid, etc, and a water-soluble organic substance, eg, ethylene glycol, glycerine, etc, under the conditions: the inclusion of air or N2 together with an air entrainer or a foaming agent, eg, saponin, soap, etc, and hydrothermal reaction at 100-180 degC for 1-90min, preferably 105-140 degC for 3- 60min Thus, a light weight, homogeneous, and spherical gypsum having a diameter of 001-10mm, usually 005-1mm, and a bulk density of 001-01g/cm can be obtained And, the gypsum can be used in the manufacture of a light weight gypsum hardened material which is excellent in heat insulation property and so forth

Continuously converting method for anhydrous gypsum into gypsum

Abstract: PURPOSE:To obtain coarse gypsum crystals, which were difficult to obtain formerly, by maintaining a slurry of by-product anhydrous gypsum and an aqueous soln. of a specified hydration accelerator at a specified temp., agitating the slurry to hydrate it, pH-adjusting the hydrated slurry with a Ca compound, and separating gypsum. CONSTITUTION:Slurry 5 of by-product anhydrous sypsum 4 of a hydrofluoric acid manufacturing process and an aqueous soln. of a hydration accelerator consisting of sodium sulfate or potassium sulfate 1 and sodium chloride 2 is passed through primary hydration vessel 6 and secondary hydration vessel 7, maintained at 30 deg.C or below with refrigerator 8, and hydrated by agitation. Part of the hydrate is recycled to vessel 6 as seed crystals, and the remaining hydrated slurry is adjusted to pH 6.5-8 with quick lime or the like in vessel 10 and passed through vessel 11 and dehydrator 12 to separate gypsum 16. Soln. 14 and part of washing liq. 15 are recycled. Gypsum 16 thus obtd. is coarse crystals and can be utilized as starting material gypsum for gypsum plaster board, plaster, etc.