Showing papers on "Gypsum published in 2017"

An Important Tool With No Instruction Manual: A Review of Gypsum Use in Agriculture

Abstract: Land application of gypsum has been studied and utilized in agriculture and environmental remediation for many years. Most of the published literature has focused on gypsum application impacts on soil properties rather than crop yields. This literature review was conducted to (i) gather results from gypsum application studies relevant to crop grain yield, soil physical–chemical properties, and environmental impact; (ii) report different methods for determining gypsum application rates; (iii) suggest recommendations for future studies on land application of gypsum. Improvement in plant nitrogen use efficiency was rarely discussed as a potential mechanism for improving yield. Free Al activity has been demonstrated to be more correlated with plant yield responses to gypsum application than exchangeable Al or Al saturation. However, few authors reported Al speciation and Al activity. While gypsum is reported to improve soil chemical properties in most cases, these changes do not necessarily translate to increases in yield. Improvements in physical properties for nonsodic soils are not consistent. It is difficult to exactly determine the positive effects from gypsum application that are responsible for yield increases, since there are often many simultaneous physical and chemical changes occurring in the soil. Improvement in crop yield may be a result of an additive or synergistic effect of each of these potential changes. In addition, these potential changes, as varied as they are, appear to also vary with crop, soil type, and rainfall regime. Therefore, meta-analysis of gypsum experiments is highly recommended in order to improve gypsum recommendations across diverse environments.

Thermal and mechanical properties of gypsum plaster mixed with expanded polystyrene and tragacanth

Abstract: In this paper, the employability of waste Expanded Polystyrene Foam (EPS) as filling material in the plaster with resin added gypsum by means of revaluation has been examined. After waste EPS is collected as packaging material and disintegration according to 0–3 mm particle diameters and mixed with the gypsum of percentages; 20%, 40%, 60% and 80%. Tragacanth is added to each of this binder at 0.5%, 1% and 1.5% of the weight of the mixture in order to create artificial pores on gypsum block. The samples of 16 different combinations are produces. They are subjected to some tests to find out their properties. It is found that; the thermal conductivity, the compression and tensile strength decreases with increasing amount of EPS and tragacanth in the mixture. Produced samples must not be used in external plaster which is subjected to water against the danger of freezing as the water absorption rate was found higher than 30%. With this study, it is recommended that the samples should be used as internal plaster, insulation plaster and decoration material due to their canal opening and paint sustention features. If this plaster and decoration material is used, (i) the waste EPS will be evaluated and environmental pollution will be prevented, (ii) building heating and cooling energy will be saved.

Technical feasibility for use of FGD gypsum as an additive setting time retarder for Portland cement

Abstract: Flue gas desulfurization (FGD) gypsum was evaluated as a setting time retarder to replace the natural gypsum in the production of Portland cement (CP II E-32). The results of physical-chemistry and morphological characterization of both products showed a material of high purity, calcium sulfate dehydrate for natural gypsum, and higher percentages of bassanite (CaSO 4 ·0.6H 2 O) and hannebachite (CaSO 3 ·0.5H 2 O) with low concentrations of impurities for FGD gypsum. Based on the results, the FGD gypsum is a suitable alternative to replace natural gypsum. The setting time with FGD gypsum showed about 1 h delay compared with natural gypsum and its effect on compressive strength depend on composition of the mixtures, reaching a maximum value for the mixture of 1.4 wt% natural gypsum and 2.1 wt% FGD gypsum. According to the results of leaching and solubilization tests FGD gypsum residue was classified as a non-hazardous and non-inert.

Optimization of Enzyme-Mediated Calcite Precipitation as a Soil-Improvement Technique: The Effect of Aragonite and Gypsum on the Mechanical Properties of Treated Sand

Abstract: The effectiveness of magnesium as a substitute material in enzyme-mediated calcite precipitation was evaluated. Magnesium sulfate was added to the injecting solution composed of urea, urease, and calcium chloride. The effect of the substitution on the amount of precipitated materials was evaluated through precipitation tests. X-ray powder diffraction and scanning electron microscopy analyses were conducted to examine the mineralogical morphology of the precipitated minerals and to determine the effect of magnesium on the composition of the precipitated materials. In addition to calcite, aragonite and gypsum were formed as the precipitated materials. The effect of the presence of aragonite and gypsum, in addition to calcite, as a soil-improvement technique was evaluated through unconfined compressive strength tests. Soil specimens were prepared in polyvinyl chloride cylinders and treated with concentration-controlled solutions, which produced calcite, aragonite, and gypsum. The mineralogical analysis revealed that the low and high concentrations of magnesium sulfate effectively promoted the formation of aragonite and gypsum, respectively. The injecting solutions which produced aragonite and calcite brought about a significant improvement in soil strength. The presence of the precipitated materials, comprising 10% of the soil mass within a treated sand, generated a strength of 0.6 MPa.

Removal characteristics of sulfuric acid aerosols from coal-fired power plants

Abstract: With increasing attention on sulfuric acid emission, investigations on the removal characteristics of sulfuric acid aerosols by the limestone gypsum wet flue gas desulfurization (WFGD) system and the wet electrostatic precipitator (WESP) were carried out in two coal-fired power plants, and the effects of the WFGD scrubber type and the flue gas characteristics were discussed. The results showed that it was necessary to install the WESP device after desulfurization, as the WFGD system was inefficient to remove sulfuric acid aerosols from the flue gas. The removal efficiency of sulfuric acid aerosols in the WFGD system with double scrubbers ranged from 50% to 65%, which was higher than that with a single scrubber, ranging from 30% to 40%. Furthermore, the removal efficiency of WESP on the sulfuric acid aerosols was from 47.9% to 52.4%. With increased concentrations of SO3 and particles in the flue gas, the removal efficiencies of the WFGD and the WESP on the sulfuric acid aerosols were increased.Impl...

Gypsum solubility in water at 25°C

Abstract: The analysis of published data and our experimental results showed that the existing estimates of gypsum solubility in water (C m ↑) at 25°C range from 0.0147 to 0.0182 M. Such a scatter (more than 20%) is the result of a combined influence of experimental conditions and ability of gypsum to form supersaturated solutions. This influence appears most noticeable during gypsum dissolution in a dispersed state. Under such conditions, equilibrium is determined with a precision of no better than ±4.5%; if a flat surface similar to natural one is dissolved, the (C m ↑) value is characterized by the minimum scatter (±1%). According to experimental data (25°C), the solubility of gypsum particles in water is inversely proportional to their size at r < 1 μm and is r-invariant for larger grains. The invariance of (C m ↑) at r > 1–5 μm is supported by the data of analytical calculations using the approximate Ostwald–Freundlich equation. It is supposed that the difference of the concentrations of dissolved gypsum at the boundaries of the field of metastable state of gypsum-saturated groundwater can be 1–5%. The results of our study can be used for the description of gypsum dissolution in the models of mass transfer between gypsum-bearing rocks and groundwater.

Synthesis of α-CaSO4·0.5H2O from flue gas desulfurization gypsum regulated by C4H4O4Na2·6H2O and NaCl in glycerol-water solution

Abstract: A brand new method to transform flue gas desulfurization gypsum (FGD gypsum) into α-calcium sulfate hemihydrate (α-HH) with short hexagonal prisms mediated by succinic acid disodium salt hexahydrate (C4H4O4Na2·6H2O) and NaCl in glycerol-water solution is studied, in which the appropriate reaction temperature is 90 °C. The addition of NaCl facilitates the dissolution of calcium sulfate dihydrate (DH) and creates much higher supersaturation which is a greater driving force for the phase transformation from DH to α-HH. C4H4O4Na2·6H2O as the crystal modifier effectively suppresses the α-HH crystal growth along the c axis, and the products generally change from needle-like particles to fat and short hexagonal prisms, which is attributed to the preferential adsorption of C4H4O42− on the top facets of the crystals by chelating Ca2+.

Dolomitization, gypsum calcitization and silicification in carbonate–evaporite shallow lacustrine deposits

Abstract: This paper describes and interprets the mineral and facies assemblages that occur in carbonate–evaporite shallow lacustrine deposits, considering the importance of the processes pathway (i.e. dolomitizacion, gypsum calcitization and silicification). The Palaeogene deposits of the Deza Formation (Almazan Basin, central-northern Spain) are selected as a case study to determine the variety of physico-chemical processes taking place in carbonate–evaporite shallow lakes and their resulting diagenetic features. Dolostones are the predominant lithology and are composed mainly of dolomite with variable amounts of secondary calcite (5 to 50%), which mainly mimic lenticular gypsum (pseudomorphs). Five morphological types of dolomite crystal were identified: dolomite tubes, dolomite cylinders, rhombohedral dolomite, spheroidal and quasi-rhombohedral dolomite and cocoon-shaped dolomite. The dolomite cylinders and tubes are interpreted as the dolomitized cells of a widespread microbial community. The sequence of diagenetic processes started with growth of microlenticular interstitial gypsum in a calcareous mud deposited on the playa margin mudflats, and that sometimes included microbial sediments. Immediately following growth of gypsum, dolomite replaced the original calcite (aragonite?) muds, the microbial community and the gypsum. Partial or total replacement of gypsum by dolomite was related mainly to the biomineralization of endolithic microbial communities on gypsum crystals. Later calcitization took place under vadose, subaerial exposure conditions. The development of calcrete in distal alluvial settings favoured the release of silica and subsequent silicification on the playa margin mudflats. Stable isotope compositions of calcite range range from -9.02 to -5.83‰ δ13CPDB and -7.10 to 1.22‰ δ18OPDB; for the dolomite these values vary from -8.93 to -3.96‰ δ13CPDB and -5.53 to 2.4‰ δ18OPDB. Quartz from the cherts has δ18OSMOW values ranging from 27.1 to 31.1‰. Wide variation and relatively high δ18OSMOW values for dolomite indicate evaporitic and closed hydrological conditions; increased influx of meteoric waters reigned during the formation of secondary calcite spar. This article is protected by copyright. All rights reserved.

Removal of sulfate by fluidized bed crystallization process

Abstract: This study investigated the behavior of sulfate removal and gypsum crystallization in an FBR with varying seed dosage, initial sulfate concentration and calcium to sulfate concentration ratio. The effect of recycling and use of silica carriers were also evaluated. A bench-scale glass fluidized-bed reactor (FBR) with gypsum seed crystals was used. Results showed that sulfate removal and gypsum crystallization increased with the tested parameters. Sulfate conversion increased from 70.29% to 77.69% and sulfate removal from 52.34% to 65.87% when seed dosage was increased from 4.0 g/L to 11.0 g/L. Similar trend was observed when the initial sulfate concentration was increased from 80 mM to 160 mM, sulfate conversion also increased from 75.05% to 85.40% and removal from 55.29% to 77.88%. When calcium to sulfate concentration ratio was increased from 1.0 to 2.0, sulfate conversion increased from 70.40% to 79.19% and removal increased from 49.45% to 65.08%. Product crystals and silica sand carriers were found to be as effective as fresh gypsum seed crystals, hence, the potential for economic recovery of sulfate.

Physicochemical and Additive Controls on the Multistep Precipitation Pathway of Gypsum

Abstract: Synchrotron-based small- and wide-angle X-ray scattering (SAXS/WAXS) was used to examine in situ the precipitation of gypsum (CaSO4·2H2O) from solution. We determined the role of (I) supersaturation, (II) temperature and (III) additives (Mg2+ and citric acid) on the precipitation mechanism and rate of gypsum. Detailed analysis of the SAXS data showed that for all tested supersaturations and temperatures the same nucleation pathway was maintained, i.e., formation of primary particles that aggregate and transform/re-organize into gypsum. In the presence of Mg2+ more primary particle are formed compared to the pure experiment, but the onset of their transformation/reorganization was slowed down. Citrate reduces the formation of primary particles resulting in a longer induction time of gypsum formation. Based on the WAXS data we determined that the precipitation rate of gypsum increased 5-fold from 4 to 40 °C, which results in an effective activation energy of ~30 kJ·mol−1. Mg2+ reduces the precipitation rate of gypsum by more than half, most likely by blocking the attachment sites of the growth units, while citric acid only weakly hampers the growth of gypsum by lowering the effective supersaturation. In short, our results show that the nucleation mechanism is independent of the solution conditions and that Mg2+ and citric acid influence differently the nucleation pathway and growth kinetics of gypsum. These insights are key for further improving our ability to control the crystallization process of calcium sulphate.

The influence of variable gypsum and water content on the strength and hydration of a belite-calcium sulphoaluminate cement

Abstract: The relative impact and interaction of two components, gypsum and water, in high ye’elimite containing calcium sulphoaluminate-belite cement pastes at an age of 7 days was studied to find the optimum conditions for compressive strength. Using statistical analysis of 149 compressive strength results having a range of water and gypsum contents, the statistical significance of the variables was investigated. X-ray diffraction analysis demonstrated the different hydration processes occurring within samples based on water and gypsum contents, while mercury intrusion porosimetry comparison confirmed the importance of pore structure towards determining ultimate paste strength. Thermodynamic modelling was also used to contribute to the understanding of the microstructural development. The compressive strengths of cement pastes with varying gypsum and water content were shown to be influenced by both factors, with a non-linear dependence on gypsum content observed.

Carbonation of gypsum from wet flue gas desulfurization process: experiments and modeling.

Abstract: In this paper, waste gypsum from wet flue gas desulfurization (WFGD) mixed with NH3·H2O was applied for CO2 absorption in the solid-liquid-gas phase system. The effects of operation temperature, CO2 flow rates, and ammonia-to-gypsum ratio on carbonation process were discussed. Meanwhile, a model for CO2 absorption in the suspension of WFGD gypsum and ammonia was established. The results indicate that higher temperature favors the reaction, and WFGD gypsum conversion can be achieved above 90% even at lower ammonia-to-gypsum ratio, while CO2 conversion reaches 90% and ammonia utilization is up to 83.69%. The model fits well with the experimental results at various CO2 flow rates and predicts the concentration distribution of the main species, including CO2 absorbed, NH2COO-, and HCO3-.