Calcium Sulfate Dehydrate Research Articles

Annual Performance Evaluation of a Novel Industrial-scale Solar Dryer for Phosphogypsum Waste

Introduction: Solar drying is considered one of the most promising technologies for drying the phosphogypsum “Calcium Sulfate Dehydrate” material as a clean source of energy and saving the environment from its negative impact if it is dried in an open landfill. Method: The dried phosphogypsum (PG) may be recycled and utilized in many useful applications. The presented design of the trapezoidal-shaped greenhouse solar dryer is the preferable solution to perform the drying process in the daytime with solar energy. It may be usable at night, during cloudy and rainy periods, using evacuated tube solar collectors via sensible heat solar thermal energy storage. The system can be operated for 24 hours by solar energy. From theoretical calculations, it was found that the drying time decreased as the gypsum layer in the drying trays decreased due to the improvement of the heat transfer mechanism. The designed solar dryer was studied at various loading capacities depending on the gypsum thickness on the dryer trays. Capacities were 8280 kg, 6624 kg, 4968 kg, 3312 kg, and 1656 kg, corresponding to gypsum thickness of 5 cm, 4 cm, 3 cm, 2 cm, and 1 cm, respectively. The daily collected amount of water and the daily moisture content were estimated with different gypsum thicknesses during all months of the year. Result: It was found that the solar dryer with a capacity of 1,656 kg weight was technically and economically feasible. It was also found that the maximum reduction of moisture content occurred during the summer season, while the minimum values were achieved during winter. Conclusion: With a mass of gypsum equal to 1,656 kg weight, the moisture content of gypsum started to decrease from its initial value (35%) until it reached the final value (10%) in 4 scenarios: the first one, 2 days from April to September, 3 days from March to November, more than 3 days in other months while the minimum moisture content, i.e., 20%, was reported in the first day in June.

Recycling thermal modified phosphogypsum in calcium sulfoaluminate cement: Evolution of engineering properties and micro-mechanism

The phosphogypsum (PG) can be used as a substitute for calcium sulphoaluminate cement (CSC) due to its high content of calcium sulfate dehydrate. In this study, the engineering properties including setting time, compressive strength and fluidity index of CSC with addition of thermal modified phosphogysum (MPG) were experimentally investigated. Furthermore, the micro-mechanisms including crystalline phase and microstructure evolutions of CSC incorporating MPG under different thermal treatment temperatures were analyzed via conducting X-ray diffraction (XRD), heat of hydration, thermogravimetry (TG) and scanning electron microscopy (SEM) tests. The results show that the optimum PG content and thermal modification temperature were respectively 10% and 300℃, which achieved the maximum compressive strength of 41.59 MPa. The hydration heat release peak of CSC with 300℃ MPG was advanced, contributing to shorter setting time and poor fluidity of CSC. Whereas after incorporating untreated and 100℃ MPG, the hydration exothermic peak of CSC lagged behind, causing higher retarding effect and better fluidity. The main hydration products of ettringite (AFt) and alumina gel (AH3) in CSC-MPG mixture were respectively produced in the early and later stages, which were similar to that in pure CSC. The amount of AFt was the most under the optimum incorporation of 10% MPG at 300℃, which was mainly responsible for the highest structure density. The key findings in this study can achieve the double benefits of utilizing waste PG and improving the engineering properties of CSC.

Preparation of calcium carbonate nanoparticles from waste carbide slag based on CO2 mineralization

This study proposes a novel method for simultaneously dealing with the waste carbide slag (WCS) and CO2 mitigation. In addition, the ultrafine vaterite CaCO3 with high economic value was produced under mild conditions of 25 °C and 0.1 MPa. Ammonium sulfate ((NH4)2SO4) was employed to efficiently extract calcium from WCS into the solid phase calcium sulfate dehydrate (CaSO4·2H2O). Subsequently, it was subjected to “dropwise carbonation” leading to the formation of a calcium carbonate with controllable particle size between 100 nm–1 μm through multiple crystalline phase transformations. The results showed that nano-sized CaCO3 with nearly 90% purity and whiteness was prepared at 25 °C, CO2-500 mL/min, and NH4+/Ca2+ = 2.4 conditions. Results of TG and FTIR analyses confirmed that CaCO3 polymorphs with vaterite and metastable were formed. Based on the calcium conversion ratio of the entire process, treatment with 1 ton of WSC captured ∼0.5 tons of CO2 and yields about 1.15 tons of nano-sized CaCO3 per each cycle operation. This study provides a valuable method for identifying potential application for scale preparation of vaterite nanoparticles from low cost but abundant calcium resource such as WCS and gypsum.

Influence of Impurities on the Process of Obtaining Calcium Carbonate during the Processing of Phosphogypsum.

The article is devoted to the study of the influence of residual sulfuric and phosphoric acids on the process of processing large-tonnage phosphogypsum (PG) waste into calcium carbonate. In the Russian Federation, about 10 percent of existing phosphogypsum waste is processed into construction materials. Acidic impurities (phosphoric and sulfuric acids) in their composition are an obstacle to the use of phosphogypsum for the production of binders. This study finds that impurities also reduce the chemical activity of phosphogypsum. At the same time, the paper focuses on the potential of phosphogypsum for the production of calcium carbonate. This article investigated the amount of impurities in phosphogypsum. The results show that during automatic washing of phosphogypsum, losses are approximately 30–35 wt. %. It was also found that phosphogypsum by 22% consists of impurities of phosphoric and sulfuric acid. These acids are characteristic waste products of extraction phosphoric acid (EPA) production. By ASTM C471M-20ae1, the content of calcium sulfate dehydrate and hemihydrate before and after washing was determined. A thermodynamic calculation of the proposed interaction of phosphogypsum with carbonates showed that the characteristic reaction is possible. The conversion process of phosphogypsum to get the corresponding calcium carbonate was carried out at 70 °C. Data on the chemical composition of the reaction products, obtained by X-ray fluorescence analysis on a Shimadzu EDX-7000 spectrometer, showed that some reactions proceed incompletely and need the selection of optimal conditions. The potential commercial benefits of processing phosphogypsum by carbonization were defined for products such as calcium carbonate or its derivatives.

Phase Transformation of FGD By-Product into Plaster Mould via Heat Treatment Process

Flue Gas Desulfurization (FGD) is a waste incineration process commonly used to eliminate sulfur dioxide (SO2) from flue gas power plants. FGD by-product recorded a rich gypsum content, also known as calcium sulfate dehydrate (CaSO4•2H2O), which has promising practical applications in plaster mould production. Plaster of Paris (POP) with a chemical composition of calcium sulfate hemihydrate (CaSO4•0.5H2O) is widely used in plaster mould production because of its quick setting and hardening upon moistened. Naturally, gypsum with 2 molecules of crystalline water can change to 1.5 molecules via the dehydration process. Various dehydration methods were conducted to transform FGD gypsum to hemihydrate. After undergoing different autoclave processes, the phase transition of FGD by-products was identified by X-ray diffraction (XRD) mode and compared with commercial POP. Chemical composition of FGD sludge contains a high amount of calcium oxide (CaO), sulfur trioxide (SO3) and boron trioxide (B2O3), as well as other impurities such as fluorine (F), chlorine (Cl), and magnesium oxide (MgO). Based on phase analysis, sample H1 to H5 show the percentage of hemihdyrate is 1.5%, 19.7%, 2.8%, 1.2%, and 46.1%, respectively, after different dehydration methods.

Application of Micro–Nano Bubbles to Improve the Performance of Reverse-Osmosis Membrane against the Gypsum Scaling

AbstractThe present study investigated the effects of air micro–nanobubbles (AMNBs) on calcium sulfate dehydrate (gypsum) scaling over a reverse-osmosis (RO) membrane in a lab-scale plate-and-frame...

Characterisation Of FGD Sludge From One of Glass Industrial in Malaysia and Their Potential as Ceramic Mould

Flue Gas Desulfurization (FGD) is a waste incineration process used to eliminate sulfur dioxide (SO2) from flue gas power plants. Limestone/gypsum was injected into the plant to trap sulfur dioxide and change their chemical composition from calcium carbonate to calcium sulfate dehydrate, known as FGD sludge wet scrubber. Nowadays, it is necessary to overcome the environmental pollution caused by the massive production of FGD sludge waste through recycling. In this research, FGD sludge was characterised to reveal its chemical composition, crystalline phase, and FTIR spectra characteristics. FGD sludge recorded a moderate alkaline with a pH of 8.24. Based on the XRD result, FGD sludge was mainly composed of gypsum (CaSO4•2H2O) and anhydrite (CaSO4). XRF analysis also shows that FGD sludge was mainly composed of calcium oxide, sulfur trioxide, silica, and potassium oxide.

Behaviour of Aquaporin Forward Osmosis Flat Sheet Membranes during the Concentration of Calcium-Containing Liquids.

This study aims to examine the scaling and performance of flat sheet aquaporin FO membranes in the presence of calcium salts. Experiments showed that the application of calcium sulphate (CaSO4) resulted in an 8–78% decline in the water flux. An increase in the cross-flow velocity from 3 to 12 cm/s reduced the decline in the flux by 16%. The deposition of salt crystals on the membrane surface led to the alteration in the membrane’s intrinsic properties. Microscopy, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and X-Ray fluorescence (XRF) analyses confirmed measurements of the zeta potential and contact angle. The use of a three-salt mixture yielded severe scaling as compared with the application of calcium sulphate dehydrate (CaSO4 × 2H2O), i.e., a result of two different crystallisation mechanisms. We found that the amount of sodium chloride (NaCl), saturation index, cross-flow velocity, and flow regime all play an important role in the scaling of aquaporin FO flat sheet membranes.

Effect of treatment time on development of gypsum carbonated apatite biphasic granules at different salt solution concentration

Abstract Sintering is the common method for heat treatment of bio ceramic implant. However this procedure is reported not appropriate for fabrication carbonated apatite due to carbonate ions are easily decomposed at above 600°C A carbonated apatite (CO3AP) ceramics was discovered to have a closer chemical composition which is similar to the bone mineral. These materials have high potential to be a good artificial bone substitute due good resorption and bioactivity properties. This study was to evaluate the effect of treatment time on phase transformation of gypsum-carbonated apatite biphasic granules which was prepared with salt solution at different concentration. Gypsum or also known as calcium sulphate dehydrate (CSD) granules were immersed into two different concentration of carbonated and phosphate mixture salt solution which is 0.5 molar and 2.0 molar respectively and undergo hydrothermal reaction at 50 °C at different treatment times. Characterization of the biphasic granules obtained were determined by multiple analytical methods such X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infra-red (FTIR), and CHN analysis. The experiment result has shown that the treated CSD was successfully transformed into carbonated apatite layer to form biphasic granules. The content of carbonated (CO32-) ion in biphasic granules prepared using salt solution at high concentration is higher than at low concentration. Thickness of carbonated apatite layer and the content of carbonated (CO32-) in biphasic granules were indicated to increase slowly by increasing hydrothermal heating time. Briefly, the concentration of salt solution and treatment time could influence the development of transformation phase of gypsum into gypsum-carbonated apatite biphasic granule.

Rheological and Mechanical Properties of Thermoresponsive Methylcellulose/Calcium Phosphate-Based Injectable Bone Substitutes.

In this study, a novel injectable bone substitute (IBS) was prepared by incorporating a bioceramic powder in a polymeric solution comprising of methylcellulose (MC), gelatin and citric acid. Methylcellulose was utilized as the polymeric matrix due to its thermoresponsive properties and biocompatibility. 2.5 wt % gelatin and 3 wt % citric acid were added to the MC to adjust the rheological properties of the prepared IBS. Then, 0, 20, 30 and 50 wt % of the bioceramic component comprising tetracalcium phosphate/hydroxyapatite (TTCP/HA), dicalcium phosphate dehydrate (DCPD) and calcium sulfate dehydrate (CSD) were added into the prepared polymeric component. The prepared IBS samples had a chewing gum-like consistency. IBS samples were investigated in terms of their chemical structure, rheological characteristics, and mechanical properties. After that, in vitro degradation studies were carried out by measurement of pH and % remaining weight. Viscoelastic characteristics of the samples indicated that all of the prepared IBS were injectable and they hardened at approximately 37 °C. Moreover, with increasing wt % of the bioceramic component, the degradation rate of the samples significantly reduced and the mechanical properties were improved. Therefore, the experimental results indicated that the P50 mix may be a promising candidates to fill bone defects and assist bone recovery for non-load bearing applications.

Utilization of flue gas desulfurization gypsum for producing calcium sulfoaluminate cement

With the rapid development of industries, flue gas desulfurization (FGD) gypsum has become one of the bulk industrial solid wastes which trigger many local environmental problems in China. Due to the high purity of calcium sulfate dehydrate, FGD gypsum has a high potential for eco-friendly calcium sulfoaluminate (CSA) cement manufacture. This would reduce nature resource and energy consumption in cement industry, and bring economic and ecological benefits for waste management. Given the high sensitivity of hydrates to the temperature, the hydration features of FGD gypsum blended CSA cement under usual climate temperature (0, 10, 20 and 40 °C) were identified by using calorimetry, XRD and DSC-TGA analysis in this work. Meanwhile, the compressive strengths and dimensional stability of prepared pastes were measured in an effort to correlate the overall performance with microstructure development. Results demonstrate that the hydration of CSA cement is highly dependent on the variations of FGD gypsum dosage and curing temperature. The addition of FGD gypsum contributes to more ettringite and alumina hydroxide generated under all curing regimes, and restrains the formation of monosulfate and strätlingite at 40 °C. Therefore, it favors the strengths development of those pastes cured at 40 °C. Additionally, moderate dosage of FGD gypsum leads to the lowest shrinkage. As a by-product generated from industry, utilizing the FGD gypsum in CSA cement production is a promising and value-added way for waste management, especially when the products applied under high temperature climate region.

Analysis of Airborne Dust as a Result of Plaster Cast Sawing.

Plaster splints are used daily in surgical and orthopedic fields in order to immobilize injured children and adults. The aim of this study was to measure the aerodynamic diameter and concentration of dust particles in the air caused by sawing plaster splints (calcium sulfate dehy-drate). We performed fractional measurements of airborne dust particles. The measured particles, which can potentially be inhaled, may have a specific negative effect on human health. Measurements were conducted in laboratory research facilities that simulated hospital conditions within a casting room and the associated waiting room. Measurements within the casting room were made using two particle collector devices and one laser photometer. The measurement for the simulated waiting room was performed using the same principles and devices. The collected plaster dust particles differed in aerodynamic diameter and concentration according to the various locations observed. The highest concentration of particles of all sizes was recorded at the site of cast sawing. There was direct correlation between distance from the source and concentration of airborne particles; this concentration was lowest in the waiting room. The concentrations of plaster dust recorded were lower than the recommended minimal limit values for total and respiratory fractions in Croatia. Accordingly, it can be assumed that sawing of plaster splints has no harmful health effects on the exposed patients and health personnel.

Optimizing the characteristics of calcium sulfate dihydrate in the flue gas desulfurization process: Investigation of the impurities in slurry-Cl-, Fe3+, Mn2+

The effects of limestone, Cl-, Fe3+ and Mn2+ in slurry on the characteristics of calcium sulfate dehydrate (DH) in flue gas desulfurization (FGD) process were investigated. The moisture content, particle size distribution, and crystal morphology were considered as end use characteristics of DH. As a result, the number of needle-like DH crystals was increased with increasing total contents of MgCO3, Al2O3 and Fe2O3 in limestone. Cl ions were reported to distort the crystal structure and change the crystals from orthorhombic to irregular. Mn2+ can increase the desulfurization efficiency by catalyzing the oxidation of SO2. Finally, Fe3+ will inhibit crystal growth of all faces, except {011} and {111}.

Use of Deep Peat-Processing Products for Hydrophobic Modification of Gypsum Binder

The article deals with the issue of gypsum binder quality reduction during its storage and transportation. The study provides the main methods to protect gypsum from unauthorized exposure to moisture and water vapor. The author proposes hydrophobic modification as a perspective method for the preservation of gypsum activity and its water absorption reduction. The substantiation of cement hydrophobization with the bitumen released during peat thermolysis is provided. The author proposes to use this method in the technology of gypsum binder production. The basic idea is to combine the hydrophobization process with the calcination of calcium sulfate dehydrate. This is facilitated by temperature ranges used for dehydration of natural gypsum and the initial stage of thermal decomposition of the organic matter of peat. The author defined experimentally an optimal concentration of the organic component in gypsum binder. After adding 0.5-1% of the peat additive, the gypsum plaster preserved its grade strength and increased its storage time without caking and hydration, also under adverse conditions. The proposed method is adapted to the technological processes presently used in the production and doesn’t require changing any equipment. The price of mineral raw materials and semi-finished products of peat are approximately equal which reduces the probability of increasing of the cost of hydrophobically modified gypsum binder.

THE DIFFERENCE ON COMPRESSIVE STRENGTH AND DIMENSIONAL CHANGE OF COMMERCIALLY TYPE III GYPSUM COMPARED TO RECYCLE GYPSUM TYPE III TO PRODUCE WORKING CAST

Gypsum is derived from pure calcium sulfate dehydrate which is a common material that is commonly used in denture manufacturing process. This study aimed to know the difference on compressive strength and dimensional change of commercially type III gypsum compared to recycle type III gypsum to produce working cast. The type of research is laboratory experiment. A total of 40 samples for each test is divided into five groups which consists of commercial type III gypsum, pure recycled type III gypsum, pure recycled type III gypsum with 10%, 20%, 30% type III commercial gypsum. The difference on compressive strength and dimensional change between the groups was analyzed using one way ANOVA and is them tested with LSD test. The result showed that there was a significant difference (p<0,05) between compressive strength and dimensional change of commercial type III gypsum compared to pure recycled type III gypsum and pure recycled type III gypsum with 10%, 20% and 30% type III commercial gypsum. In conclusion, addition of 30% commercial gypsum in recycled gypsum the compressive strength was higher than other recycled gypsum types.

A study on the impact of SO2 on CO2 injectivity for CO2 storage in a Canadian saline aquifer

Potential effects of SO2 as an impurity on CO2 injectivity for CO2 storage in a targeted sandstone saline aquifer in western Canada were investigated. Batch experiments using rock and brine samples in contact with supercritical CO2 and CO2 mixtures with SO2 were conducted in high-pressure reactors for 45days. The results suggest that SO2 increased precipitation of sodium chloride and calcium sulfate dehydrate, and also increased the dissolution of quartz. Moreover, the precipitation of sodium chloride appeared to be concurrent with the dissolution of quartz, the predominant constituent of the rock. The concurrent precipitation of sodium chloride and dissolution of quartz could be attributed to taking up of water by H4SiO4 that reduces the number of water molecules in the hydration shells of Na+ and Cl− ions in highly concentrated brine. According to this view, the dissolution of quartz, which would be much slower than the reassociation of dissolved sodium chloride ions, is limiting the rate of sodium chloride precipitation. The rate of quartz dissolution was estimated based on the present experimental data, which could be used to assess salt precipitation and determine suitable operation conditions for CO2 injection. The findings of this work should also be applicable to acid gas injection in oil and gas industry.

Double-Hydrophilic Block Copolymer as an Environmentally Friendly Inhibitor for Calcium Sulfate Dehydrate (Gypsum) Scale in Cooling Water Systems

Abstract In this study, a novel environmentally friendly copolymer acrylic acid-itaconic acid-allylpolyethoxy maleic carboxylate was synthesized and used for inhibiting the calcium sulfate dehydrate (gypsum) scale. The properties of the synthesized copolymer were characterized by Fourier-transform infrared, nuclear magnetic resonance spectroscopy and thermal gravity analysis. Also, the structure and morphology changes of scale crystals were studied by scanning electronic microscopy, transmission electron microscopy and X-ray powder diffraction analysis. The copolymer inhibition ability was evaluated by means of static scale inhibition experiments. Results show that the copolymer was effective in inhibiting the scales by changing the size and morphology of the crystals. The maximum inhibition efficiency was 99.8% at a concentration of 2 mg · L– 1, far more efficient than most commercial inhibitors.

Synthesis of calcium sulfate hemihydrate whiskers using oyster shells

Herein, the feasibility of preparing long and homogeneous hemihydrate (HH) whiskers using waste oyster shell was investigated. The whiskers formed from the sintered raw material had higher aspect ratios and more uniform morphology than non-sintered. The effect of reaction temperature, reaction time, and concentration were investigated. It was found that the optimum reaction temperature, reaction time, and concentration for stable and well-grown whiskers were 140 °C, 5 h, and 4 wt%, respectively. Direct transition from calcium sulfate dehydrate (DH) to HH was detected by X-ray diffraction (XRD) patterns, and the result showed DH completely transformed to HH after 5 h. The preferred direction of growth along the c-axis was confirmed by XRD pattern, selected area diffraction pattern, and high-resolution transmission electron microscopy (HRTEM).

Spectral Analysis of Trace Fluorine Phase in Phosphogypsum

Phosphogypsum, which contains more than 90% of the calcium sulfate dehydrate (CaSO4 · 2H2O), is a kind of important renewable gypsum resources. Unlike the natural gypsum, however, phosphorus, fluorine, organic matter and other harmful impurities in phosphogypsum limit its practical use. To ascertain the existence form, content and phase distribution of trace fluoride in phosphogypsum has important theoretical values in removing trace fluoride effectively. In this present paper, the main existence form and phase distribution of trace fluoride in phosphogypsum was investigated by the combination of X-ray photoelectron spectroscopy (XPS) and Electron microprobe analysis (EMPA). The results show that trace fluoride phase mainly includes NaF, KF, CaF2, K2SiF6, Na2SiF6, Na3AlF6, K3AlF6, AlF3 · 3H2O, AlF2.3(OH)0.7 · H2O, Ca5(PO4)3F, Ca10(PO4)6F2. Among them, 4.83% of fluorine exists in the form of fluoride (NaF, KF, CaF2); Accordingly, 8.43% in the form of fluoride phosphate (Ca5(PO4)3F, Ca10(PO4)6F2); 12.21% in the form of fluorine aluminate (Na3AlF6, K3AlF6); 41.52% in the form of fluorosilicate (K2SiF6, Na2SiF6); 33.02% in the form of aluminum fluoride with crystal water (AlF3 · 3H2O, AlF2.3(OH)0.7 · H2O). In the analysis of phase constitution for trace elements in solid samples, the method of combining XPS and EMPA has more advantages. This study also provides theoretical basis for the removal of trace fluorine impurity and the effective recovery of fluorine resources.

Analysis of Physical and Chemical Features of Sintering Dust and Study of Recycling Treatment

Several physical and chemical detection methods were used to study the basic properties of sintering dust collected from Baogang Steel Corporation. The result shows that the major constituents of the electrostatic precipitator dust (ESP dust) were KCl, NaCl, Fe2O3 and Fe3O4. Water leaching experiment on the sintering dust had shown that the KCl in the ESP dust could be separated and recovered by water leaching and fractional crystallization. Component analysis of leaching solution showed that the massive calcium sulfate in the leaching solution should be removed first in order to obtain the pure potassium salt. In order to provide theoretical guidance to inhibit the dissolution of calcium ions from the sintering dust, the water leaching experiment of ESP dust and the dissolution behavior of CaSO4 in the potassium chloride, sodium chloride, potassium sulfate and their mixed salt solution were studied. Result showed that, a lower liquid-solid ratio should be chosen in the leaching process to inhibit the dissolution of calcium sulfate dehydrate. Using sodium carbonate solution as a precipitating agent, the influences of the concentration of sodium carbonate solution, reaction temperature, stirring speed on the preparation of the spherical calcium carbonate were studied. Spherical calcium carbonate with good dispersing performance and grain size distribution in nanometer range of less than 10μm was obtained. The production technology of potassium sulfate by double decomposition was sutdied, the results showed that over 80% and 12.76% of the recovery rate of potassium sulfate and potassium chloride ammonium compound fertilizer could be obtained. Furthermore, a potassium recovery process with joint production of spherical calcium carbonate and potassium sulfate was designed. This process is technically viable and considerable in economic benefit.