Showing papers on "Gypsum published in 2010"
TL;DR: In this article, the hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye'elimite with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling.
Abstract: Calcium sulfoaluminate (CSA) cements, which represent a CO2-friendly alternative to conventional Portland cements, are produced by blending CSA clinker with gypsum and/or anhydrite. The hydration kinetics and the hydrated phase assemblages of the main hydraulic phase ye’elimite (calcium sulfoaluminate) with calcium sulfate were studied by isothermal conduction calorimetry, thermogravimetric analysis, X-ray diffraction analysis and thermodynamic modelling. Two calcium sulfates with different reactivities (gypsum and anhydrite) were applied. It was found that the pure phase without any calcium sulfate addition exhibits very slow hydration kinetics during the first 10 h. The hydration can be accelerated by the addition of calcium sulfate or (less effective) by increasing the pH of the aqueous phase. The amount of the calcium sulfate determines the ratio between the hydration products ettringite, monosulfate and amorphous aluminium hydroxide. The reactivity of the added calcium sulfate determines the early hydration kinetics. It was found that the more reactive gypsum was better suited to control the hydration behaviour of ye’elimite.
241 citations
TL;DR: Gypsum panels composed of 100% FGD gypsum from two power plants have been subjected to different physico-chemical, mechanical, and fire resistance tests in order to determine the recycling possibilities of this kind of material in this application.
80 citations
TL;DR: Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold-water coral mound in the Porcupine Basin, off Ireland as mentioned in this paper.
Abstract: Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold-water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore-water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment-water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate-rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds.
72 citations
TL;DR: In 2008, a long core was drilled in the Qahansilatu sub-basin in the western Qaidam basin, and detailed mineralogical investigation focused on evaporite minerals including halite, gypsum, mirabilite, thenardite, glauberite, eugsterite, and bloedite as discussed by the authors.
63 citations
TL;DR: In this paper, a theoretical and experimental investigation of the solubility of gypsum and anhydrite in simulated laterite pressure acid leach (PAL) solutions was conducted in the temperature range of 25-250°C.
55 citations
TL;DR: In this article, a principal component analysis (PCA) was applied to the correlation matrix of the log-transformed data set, and the equilibrium status of 1:5 extracts with regard to gypsum was assessed with the chemical speciation programme SALSOLCHEMIS.
53 citations
TL;DR: Given the high potential of calcium mud to sequester CO(2) and of resulting calcite powder to neutralize AMD, paper wastes could be a promising solution for facing this double environmental problem.
52 citations
TL;DR: Two Arthrobacter isolates from the evaporite were used to mediate gypsum neogenesis in the laboratory, demonstrating a potential role for microbial biomineralization processes in polar environments.
Abstract: Evaporitic deposits are a globally widespread habitat for micro-organisms. The microbe–mineral environment in weathered and remobilized gypsum from exposed mid-Ordovician marine evaporite beds in the polar desert of Devon Island, Nunavut, Canadian High Arctic was examined. The gypsum is characterized by internal green zones of cyanobacterial colonization (dominated by Gloeocapsa/Aphanothece and Chroococcidiopsis spp. morphotypes) and abundant black zones, visible from the surface, that contain pigmented cyanobacteria and fungi. Bioessential elements in the gypsum are primarily provided by allochthonous material from the present-day polar desert. The disruption, uplift and rotation of the evaporite beds by the Haughton meteorite impact 39 Ma have facilitated gypsum weathering and its accessibility as a habitat. No cultured cyanobacteria, bacteria and fungi were halophilic consistent with the expectation that halophily is not required to persist in gypsum habitats. Heterotrophic bacteria from the evaporite were slightly or moderately halotolerant, as were heterotrophs isolated from soil near the gypsum outcrop showing that halotolerance is common in arctic bacteria in this location. Psychrotolerant Arthrobacter species were isolated. No psychrophilic organisms were isolated. Two Arthrobacter isolates from the evaporite were used to mediate gypsum neogenesis in the laboratory, demonstrating a potential role for microbial biomineralization processes in polar environments.
41 citations
TL;DR: In this paper, the effect of added Ca-hydroxide to gypsum, carbonation periods, and hydrothermal temperatures for phosphatization was investigated to understand the basic principle of composition-transformation of gypsuma added Cahydroxides to fabricate CHA bone substitutes.
39 citations
TL;DR: In this article, the influence of ground gypsum mineral (GGM) as an accelerator and citric acid as a retarding agent in the hydration of the β form of plaster is explored.
Abstract: In this article, we use rapid two-dimensional nuclear magnetic resonance T1–T2 relaxation time correlations to monitor hydration kinetics, microstructural evolution, and surface interactions simultaneously in gypsum plaster pastes of industrial relevance. In particular, we explore the influence of ground gypsum mineral (GGM) as an accelerator and citric acid as a retarding agent in the hydration of the β form of plaster. Quantitative relative water fractions are determined and the modified hydration processes are observed as expected. These measurements also reveal the evolution of a secondary water population in the presence of the retarding agent when sedimentation of the hemihydrate occurs prior to crystallisation. In these samples, the ratio of relaxation times T1/T2 provides an indication of both the number and the strength of interactions between water molecules and solid gypsum particles. It is observed that the GGM decreases the T1/T2 ratio, whilst the citric acid increases the T1/T2 ratio, relative to the T1/T2 ratio in the unmodified plaster paste. We interpret this as an increase in the water–hemihydrate interaction in the presence of GGM, and a decrease in the presence of citric acid, consistent with the current understanding of the behaviour of these additives as an accelerator and retardant, respectively. The T1 relaxation time measurements provide an indication of the pore structure evolution: larger pores are present in the accelerated product, and smaller pores in the retarded product, compared to the unmodified plaster. These conclusions are supported by helium porosimetry and scanning electron microscopy. The rapid T1–T2 measurement described here will be applicable to other reactions that evolve on a time scale of several minutes.
39 citations
TL;DR: In this article, the authors investigated whether a plaster which has two plaster layers with different pore sizes can act as a salt accumulating plaster system, in which salt crystallizes in the base layer of the plaster and not in the substrate or at the external surface.
TL;DR: In this article, the stabilization of local peat soil from Matang, Sarawak, using gypsum and fly ash was presented, and the unconfined compressive strength (UCS) test was conducted to determine the strength gain after 7, 14 and 28 days of curing periods.
Abstract: This paper presents the stabilization of local peat soil from Matang, Sarawak, using gypsum and fly ash. Peat soil has been identified as one of the major groups of soils found in Malaysia, which has high compressibility and low shear strength. Presence of soft or peaty soil is a major problem encountered by civil engineers in Sarawak. Different percentages of gypsum (i.e., 2, 4, 6 and 8%) and fly ash (i.e., 5, 10, 15, 20 and 25%) were added into peat soil at optimum moisture content and it’s maximum dry density determined by standard Proctor test. Unconfined compressive strength (UCS) test were conducted to determine the strength gain after 7, 14 and 28 days of curing periods. Physical properties of the peat soil have also been studied for identification and classification purposes. The unconfined compressive strength test results show that the peat soil gained strength due to the addition of different percentages of admixtures such as gypsum and fly ash and the strength also increases with the increase of curing periods.
TL;DR: In this paper, a semi-rigid road sub-base is proposed, which is a mixture of FGD gypsum, water glass and slaked lime, and the experimental results showed that the road subbase material reflects excellent mechanical properties and soundness durability.
TL;DR: In this article, raw mixes containing pulverized coal fly ash (with limestone and silica sand) or fluidized bed coal combustion ash (fly and bottom, with added limestone, anodization mud, and, when necessary, flue gas desulfurization gypsum), respectively, were heated in a laboratory electric oven at temperatures ranging from 1150° to 1500°C and submitted to X-ray diffraction analysis.
Abstract: Raw mixes containing pulverized coal fly ash (with limestone and silica sand) or fluidized bed coal combustion ash (fly and bottom, with added limestone, anodization mud, and, when necessary, flue gas desulfurization gypsum), aimed at generating ordinary Portland or calcium sulfoaluminate clinkers, respectively, were heated in a laboratory electric oven at temperatures ranging from 1150° to 1500°C and submitted to X-ray diffraction analysis. The former had the same qualitative phase composition as that of a reference mixture, composed by limestone and clay; furthermore, they exhibited an excellent burnability on the basis of their residual free lime contents, measured after heating at 1350°, 1400°, 1450°, and 1500°C. The latter showed very good results in terms of conversion of reactants and selectivity degree toward the main mineralogical constituent, calcium sulfoaluminate (4CaO·3Al2O3·SO3), even if the behavior of a reference mixture consisting of limestone, bauxite, and natural gypsum was slightly bet...
TL;DR: A 16th century ceramic vessel containing a greasy substance was found in the castle of Middelburg (Belgium) as mentioned in this paper, where a wide range of chemical techniques were applied on what was presumed to be an ointment to reveal its nature and function.
TL;DR: Gypsum (CaSO 4 ·2H 2 O) deposits from a range of sedimentary environments at Guerrero Negro, Baja California Sur, Mexico were investigated for microscale texture and composition in order to differentiate features formed under substantial microbial influence from those for which microbial effects were relatively minor or absent.
TL;DR: In this article, the authors show that if gypsum prevails over anhydrite, the karst evolution cannot take place at depth and the structure of the underground drainage paths only follows near-surface paths in Gypsum.
Abstract: Poiano is the largest karst spring of the Emilia Romagna region (northern Italy). It drains an aquifer of unique properties composed of anhydrite with halite lenses at depth and gypsum at the surface (both with high NaCl content). Hydrogeological research has been undertaken using automatically recorded hourly data on temperature, electrical conductivity, and water level. Water feeding the Poiano spring is restricted within the gypsum/anhydrite outcrop between the Lucola, Sologno and Secchia rivers. Karstification in the Upper Secchia Valley only concerns the gypsum rocks mainly present along the border and in the shallower parts of the sulfate outcrop and does not appear to occur at depth. Data strongly support the hypothesis that the salt content in the spring water derives from active halokinetic movements. For the first time, the fundamental hydrogeological importance of the anhydrite part inside the sulfate rocks is demonstrated. If gypsum prevails over anhydrite the karst drainage network can extend deep into the rocks following a network of fractures and fissures. Instead, if in the deep parts of the aquifer anhydrite prevails over gypsum, the karst evolution cannot take place at depth and the structure of the underground drainage paths only follows near-surface paths in gypsum.
TL;DR: In this article, the authors used the PHREEQC program for Windows to estimate saturation indices for calcite, dolomite, gypsum and epsomite.
TL;DR: In this paper, the authors presented the studies on characterization, beneficiation and utilization of H-acid gypsum, a waste material produced by the neutralization of free sulphuric acid collected during the formation of intermediate dyes.
TL;DR: In this paper, the effect of gypsum on the solubility of 13 nutrients and how amending the soil with organic peat moss may mitigate the impact of the accumulation in gypsiferous soils on nutrients and soil fertility.
Abstract: It is widely accepted that the accumulation of gypsum in gypsiferous soils results in very low fertility, even with application of fertilizers and organic amendments. The objectives were to investigate, in laboratory experiments, the effect of gypsum on the solubility of 13 nutrients and how amending the soil with organic peat moss may mitigate the impact of gypsum on nutrients and soil fertility. A 100-g sample of gypsum-free soil (Sharpsburg Fine, montmorillonitic, mesic Typic Argiudolls) was treated with increasing amounts of gypsum (0, 1, 5, 10, 15, 20, 30, and 50 g), then water was added to the mixtures to reach 50% of the water saturation capacity. Another set of soil/gypsum mixtures received 5-g peat to study the effect of peat application. All mixtures were incubated at 32 degrees C for 15 weeks. After incubation, the concentration of water-soluble nutrients was measured. In general, the addition of gypsum increased the solubility of N, K, Ca, Mg, Mn, Cl, and S, whereas it decreased the solubility of P, Na, Fe, Cu, Zn, and B. The application of peat increased the solubility of all nutrients investigated, except for N and S. Chemical reactions and mechanisms were applied to interpret the effects of both gypsum and peat treatments on nutrient solubility and their relationship to soil fertility and crop production. The application of peat improved the solubility of most nutrients and proved to be useful as an amendment for gypsum-rich soils and increases its productivity.
TL;DR: In this article, the results of a synoptic sampling of inorganic and isotopic geochemistry of surface water and ground-water during base fl ow in Red Canyon Creek watershed (Wyoming, USA) to evaluate how mixing of waters and geochemical processes modify stream-water chemistry are reported.
Abstract: We report the results of a synoptic ("snap- shot") sampling of inorganic and isotopic geochemistry of surface water and ground- water during base fl ow in Red Canyon Creek watershed (Wyoming, USA) to evaluate how mixing of waters and geochemical processes modify stream-water chemistry. Our syn- optic approach of studying the geochem- istry of a stream mimics and has the same strengths of that widely used to characterize geochemical processes in groundwater sys- tems. Gypsum dissolution, carbonate pre- cipitation, and the infl ux of tributary and groundwater all affect Red Canyon Creek stream-water chemistry. Identical ranges of hydrogen and oxygen isotopes show good hydraulic connection between surface water and shallow groundwater. In contrast, δ 34 SSO4 values of groundwater (15.2‰ ± 1.6‰) and surface water (11.1‰ ± 1.6‰) refl ect sulfate mostly contributed by gypsum dissolution. Calcium contributed by gypsum dissolution causes calcite to rapidly precipitate in crusts observed in the streambed. This process oc- curs even though residence time of water in the stream is orders of magnitude less than that found in groundwater systems show- ing the same kind of common ion effect. Al- though microbes oxidize organic matter by sulfate reduction behind beaver dams and in the hyporheic zone, too little of this water reaches the stream to measurably affect the sulfur isotopic signature of its water. The results of this study suggest that calcareous accumulations in the fl uvial sedimentary record , in association with gypsum, may pos- sibly be paleohydrologic proxies for environ- ments where mixtures of surface water with different chemical composition occurred.
TL;DR: This study investigated the distribution of gypsum and organic matter in a sorting process and found that removing this density range after segregating fine particles should reduce the amount of Gypsum sent to landfills.
Patent•
16 Jun 2010
TL;DR: In this paper, a method for preparing calcium sulfate crystal whiskers (CaSO4) by using impurity-containing gypsum as a raw material was proposed, which can be used as reinforcing, heat insulating or flame retardant materials in industries of plastics, rubbers, coatings, papermaking, building materials and the like.
Abstract: The invention relates to a method for preparing calcium sulfate crystal whiskers (CaSO4) by using impurity-containing gypsum as a raw material The method comprises the following steps of: removing main impurities in the raw material which is the low-priced impurity-containing gypsum resource in a mode of roasting, acid-complex leaching and alkaline leaching and simultaneously thinning crystal grains to obtain a superfine dihydrate calcium sulfate precursor which is high in purity and dispersibility; and preparing the anhydrous calcium sulfate crystal whiskers with a length of 20 to 2,000mu m, a diameter of 05 to 20 mu m, a length-diameter ratio of 40 to 1,000 and a weight percent content of over 95 percent in a mode of hydrothermal conversion-roasting of a fluxing agent The method has the advantages of low-priced and easily bought raw materials, simple process, wide application range, and high added value The calcium sulfate crystal whiskers prepared by the method have a big length-diameter ratio and regular shape, and can be used as reinforcing, heat insulating or flame retardant materials in industries of plastics, rubbers, coatings, papermaking, building materials and the like
Patent•
16 Jun 2010
TL;DR: In this paper, the authors proposed a method for preparing alpha semi-hydrated gypsum by utilizing desulfurized gypsuma, comprising the technological steps of purification, crystal transforming reaction, oriented crystallization, washing and separation, and drying and pulverization.
Abstract: The invention provides a method for preparing alpha semi-hydrated gypsum by utilizing desulfurized gypsum, comprising the technological steps of purification, crystal transforming reaction, oriented crystallization, washing and separation, and drying and pulverization. The method concretely comprises the following steps of: enhancing the taste of calcium sulfate dlhy in the desulfurized gypsum to be greater than 95% through a purification treatment; dissolving and recrystallizing the desulfurized gypsum at 70 to 98 DEG C under the normal pressure through adding prepared habit modifiers, transforming into the alpha semi-hydrated gypsum and then carrying out oriented crystallization on the alpha semi-hydrated gypsum to form a short column-shaped alpha semi-hydrated gypsum crystal under the function of an oriented crystal type stabilizer, wherein the length-diameter ratio of the short column-shaped alpha semi-hydrated gypsum crystal is less than 1:3, the 2h breaking strength is greater than 6.5 MPa, the compression strength is greater than 23 MPa, the dry breaking strength is greater than 25 MPa, and the dry compression strength is greater than 53 MPa. The method can be widely used in the fields of ceramics, automobiles, precise casting, heterogenic casting and the like.
TL;DR: In this article, the geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field examples, and electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain.
Abstract: Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations, laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field examples. A geoelectrical classification of gypsum rocks defining three types of gypsum rocks has been elaborated: (a) Pure Gypsum Rocks (>75% of gypsum content), (b) Transitional Gypsum Rocks (75–55%), and (c) Lutites and Gypsum-rich Lutites ( 800 ohm.m, can be exploited as industrial rocks. The methodology used could be applied in other geoelectrical rock studies, given that this relationship between the resistive particles embedded within a conductive matrix depends on the connectivity of the matrix particles.
TL;DR: In this paper, the authors investigated the possibility of Ca2+ release from calcite and Na+ leaching from cowpea and hyacinth beans in calcareous salt affected soils.
Abstract: Increasing levels of CO2 and H+ proton in the rhizosphere from some legumes may play an important role in calcite dissolution of calcareous salt affected soils. Soils planted with white and brown varieties of cowpea (Vigna unguiculata L.) and hyacinth bean (Dolichos lablab L.) relying on either fertilizer N (KNO3) or N-fixation were compared against soils to which gypsum was applied and a control without plants and gypsum application to study the possibility of Ca2+ release from calcite and Na+ leaching. As compared to plants relying on inorganic N, leachates from all pore volumes (0·5, 1·0, 1·5, 2·0 pore volume) in lysimeters planted with N-fixing hyacinth bean contained significantly higher concentrations of HCO with lower concentrations from lysimeters planted with white cowpea relying on N-fixation. However, the lowest concentrations of HCO were recorded in the gypsum and control treatments. In initial leaching, lysimeters planted with N-fixing plants maintained similar leachate Ca2+ and Na+ concentrations compared to gypsum amended soils. However, gypsum amended soils were found to have a prolonged positive effect on Na+ removal. It might be concluded that some legumes that are known to fix N in calcareous salt affected soils may be an alternative ameliorant to the extremely expensive gypsum through calcite solubilization and a consequent release of Ca2+.
TL;DR: In this paper, the authors present the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX.
Abstract: This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed.
TL;DR: In this article, Ramaman micro-spectrometry was used for the nondestructive detection of urea in artificially prepared mineral matrices, including calcite and gypsum powders.
Abstract: Raman microspectrometry was used for the nondestructive detection of urea in artificially prepared mineral matrices. Various concentrations of urea, a possible biomarker, mixed with calcite and gypsum powders were analyzed using the 514.5-nm line of an argon laser. Two types of measurements were carried out: direct measurements of powders and analysis of the same mixtures through natural, transparent crystals of calcite and gypsum. The detection limit for urea in artificial powder mixtures was 1 wt% for both calcite and gypsum. In the case of measurements through the monocrystals, the detection limit was between 1 and 5 wt% for calcite and slightly above 5 wt% in the case of gypsum. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the SALSOLCHEMIS code for chemical equilibrium assessment was parameterized with published analytical data for aqueous synthetic calcite and gypsum-saturated solutions.
Abstract: Calcite and gypsum are salts of major ions characterized by poor solubility compared with other salts that may precipitate in soils. Knowledge of calcite and gypsum solubility products in water-saturated soil samples substantially contributes to a better assessment of processes involved in soil salinity. The new SALSOLCHEMIS code for chemical equilibrium assessment was parameterized with published analytical data for aqueous synthetic calcite and gypsum-saturated solutions. Once parameterized, SALSOLCHEMIS was applied to calculations of the ionic activity products of calcium carbonate and calcium sulphate in 133 water-saturated soil samples from an irrigated salt-affected agricultural area in a semi-arid Mediterranean climate. During parameterization, sufficiently constant values for the ionic activity products of calcium carbonate and calcium sulphate were obtained only when the following were used in SALSOLCHEMIS: (i) the equations of Sposito & Traina for the free ion activity coefficient calculation, (ii) the assumption of the non-existence of the Ca(HCO 3 ) + and CaCO 3 o ion pairs and (iii) a paradigm of total ion activity coefficients. The value of 4.62 can be assumed to be a reliable gypsum solubility product (pKs) in simple aqueous and soil solutions, while a value of 8.43 can only be assumed as a reliable calcite solubility product (pKs) in simple aqueous solutions. The saturated pastes and saturation extracts were found to be calcite over-saturated, with the former significantly being less so (pIAP = 8.29) than the latter (pIAP = 8.22). The calcite over-saturation of saturated pastes increased with the soil organic matter content. Nevertheless, the inhibition of calcite precipitation is caused by the soluble organic matter from a dissolved organic carbon threshold value that lies between 7 and 12 mM. The hypothesis of thermodynamic equilibrium is more adequate for the saturated pastes than for the saturation extracts.
Patent•
17 Feb 2010
TL;DR: In this paper, a method for preparing gypsum-based self-leveling material for use in building material industry is presented, which consists of calcining the desulfurization of desulfurized girders in a calcining kiln and mixing calcined gypsuma powder to obtain high strength, high flowability, small contraction deformation and low cost.
Abstract: The invention discloses a method for preparing gypsum-based self-leveling material for use in building material industry. The main material of the gypsum-based self-leveling material is desulfurized gypsum which is a desulfurization product from power plants. The method comprises: firstly, calcining the desulfurized gypsum in a calcining kiln; and secondly, mixing calcined gypsum powder accountingfor 50 to 78 percent of the total weight of the material, a water reducer accounting for 0.1 to 1 percent of the total weight of the material, a retarder accounting for 0.01 to 0.5 percent of the total weight of the material, a water-retaining agent accounting for 0.02 to 5 percent of the total weight of the material, a reinforcing agent accounting for 0 to 10 percent of the total weight of the material, re-dispersible emulsion powder accounting for 0.2 to 1.5 percent of the total weight of the material, a defoamer accounting for 0.05 to 0.2 percent of the total weight of the material, riversand accounting for 25 to 45 percent of total weight of the material and a filler accounting for 0 to 20 percent of the total weight of the material to obtain a the high-performance gypsum-based product. The invention provides a new method for producing high-quality gypsum-based self-leveling material characterized by high strength, high flowability, small contraction deformation and low cost by using the desulfurized gypsum, which provides a new way of comprehensively using desulfurized gypsum that is a solid waste and fills the blank that the preparation of gypsum-based self-leveling materials from desulfurized gypsum lacks in China.