Natural Gypsum Research Articles

Effect of Phosphogypsum on Soil Physical Properties in Moroccan Salt-Affected Soils

Salinity is one of the most critical challenges for crop production and soil and water management in arid and semi-arid regions, such as a large area of Morocco. These regions are characterized by low rainfall with an erratic distribution, long drought periods, and high evaporation, resulting in salt accumulation in the superficial layer of the soil and soil and water degradation. Therefore, phosphogypsum (PG) could be a promising amendment to reduce the salinity effect and improve soil quality in salt-affected soils. In this context, the present study aimed to evaluate the effect of PG on the physical properties of Luvisols and Cambisols collected from salt-affected soils in four regions in Morocco: Chichaoua, Ras El Ain, Sidi Zouine, and Sed El Masjoune. The treatments consisted of different rates of PG (15, 30, and 45 t/ha), natural Gypsum (G) (15 t/ha), and control. Our findings revealed that PG application improved soil structure by promoting flocculant action provided by calcium. Linear regression indicated that Water Aggregate Stability (WAS) and PG doses were strongly correlated with a high coefficient of determination (R2 = 93.41%, p value < 0.05). Compared to the control, the overall efficiency of 45 t/ha of PG amendment reached 53%, 95%, and 36%, respectively, in Chichaoua, Ras El Ain, and Sed El Masjoune soils. PG application presented a positive effect on other soil physical properties (soil hydraulic properties, total porosity, and bulk density), especially for the soils of Chichaoua and Ras El Ain regions. The total porosity was increased by 8% with 45 t PG/ha in Ras El Ain soil, and in Chichaoua soil, the bulk density was 5% lower in the pot treated with 45 t PG/ha compared to the control. This study supports the use of PG as an amendment for reclaiming salt-affected soils through monitoring agronomic and environmental impacts.

Preservation and modification of the isotopic composition (18O/16O and 2H/1H) of structurally-bound hydration water of gypsum (CaSO4·2H2O) in aqueous solution

Early investigations on stable isotopes (δ18O and δD) of structurally-bound gypsum (CaSO4·2H2O) hydration water (GHW) suggested that soon after gypsum precipitation, its primary isotopic composition could be altered via gypsum re-crystallization or by isotope exchange by diffusion of water into the intact crystals. If this occurs, the use of stable isotopes of GHW as a paleoclimate proxy is compromised. Here we investigated the long-term (up to 6 years) stability of GHW in contact with aqueous solution by conducting isotopic exchange experiments at different temperatures and using varying gypsum grain size. We placed gypsum with known hydration water isotopic composition in 18O/D-enriched and 18O/D-depleted aqueous solutions and monitored any change in the stable isotopes of GHW with time. At low temperature (25 °C) and when the solution is in chemical equilibrium with the mineral, GHW preserves its primary isotopic composition after 2 years. In contrast, when the gypsum-solution system is out of chemical equilibrium, the δ18OGHW and δDGHW values are altered, first via gypsum re-crystallization from the solution and later by isotope exchange via diffusion. Importantly, δ18OGHW and δDGHW stabilized after 2 years to values that represent only an 8 % change relative to the original GHW and remain constant during the subsequent 4 years. Our results suggest that at low temperature the effect of isotope exchange on GHW is limited. At higher temperature (65 °C), chemical equilibrium is not attained after 2 years for fine-grained synthetic gypsum (<250 μm) and its isotopic values continues to change. In contrast, the δ18OGHW and δDGHW in experiments using fine-grained natural gypsum at 45 °C stabilized after 1 year and values changed less than 3 % with respect to initial conditions. Experiments with coarser-grained natural gypsum (1–2 mm) at 45 °C did not show measurable isotopic changes of the GHW, indicating the lack of gypsum dissolution/re-crystallization or diffusion isotopic exchange. We conclude that microcrystalline gypsum crystals (<250 μm) are more readily affected by diagenesis resulting from changes in the gypsum saturation state of the solution, whereas larger gypsum crystals are more likely to preserve their original isotopic compositions. Our results indicate that under certain conditions, GHW can preserve the isotopic composition of its parent fluid and provide valuable information about paleoclimate and paleo-hydrologic conditions.

TESTS OF SELECTED PROPERTIES OF CONSTRUCTION MORTARS MODIFIED WITH WASTE GYPSUM BINDER OBTAINED IN THE FLUE GAS DESULPHURIZATION PROCESS

The article presents the results of tests of selected properties of plastering mortars that are based on natural gypsum binder, as well as on synthetic gypsum binder from the flue gas desulphurization process. The mortars were analyzed with regards to their durability. For the purpose of the publication, the recipe (quantitative) compositions of the plastering mortars, which differed in terms of the type of used setting retarder (PlastRetard PE and tartaric acid A200), were designed. The mortar recipes were determined experimentally, assuming that the beginning of the setting time was 120 min (the average beginning of the setting time for currently available building mortars), and that the content of the binder was 70%. The assumed research program included tests of flexural and compressive strength, surface hardness, and the adhesion to the substrate. The results of the research confirmed the possibility of modifying the recipe compositions of gypsum plastering mortars.

Influence of water on deformation and failure of gypsum rock

While water is known to significantly reduce the strength of rocks, there remains a paucity of data on water-weakening of gypsum. Here, we quantify water-weakening in a natural gypsum facies from Monferrato (Italy) by performing experiments on nominally dry, oil-saturated, and water-saturated samples. Uniaxial and conventional triaxial experiments revealed significant water-weakening in Monferrato gypsum as well as a strong strain-rate dependence of uniaxial compressive strength. Moreover, uniaxial creep tests showed significant time-dependent deformation in samples saturated with sulphate over-saturated water, but not in dry and oil-saturated samples. The creep phenomenology is similar to that observed in other rock types and is consistent with stress-corrosion microcracking, which is supported by our microstructural observations. However, we systematically recorded more inelastic strain in samples deformed at low strain-rates suggesting that additional mechanisms were also active. Comparing our new data on short-term strength with published results for other rock types, we conclude that, when saturated with water in equilibrium with the rock, weakening in gypsum is not notably higher than in other rocks and is partially due to a reduction of fracture toughness in the presence of water.

Effect of soluble phosphate, fluoride, and pH in Brazilian phosphogypsum used as setting retarder on Portland cement hydration

Phosphogypsum (PG) is a residue from the fertilizer industry used by Portland cement companies as a source of calcium sulfate to control the setting time during the hydration (or hardening process). However, certain impurities can alter the cement hydration kinetics. Thus, this paper aims to analyze the soluble phosphate, fluoride, and pH effects of Brazilian phosphogypsum used as a setting retarder on the hydration of Portland cement. Different sources of calcium sulfate were analyzed: natural gypsum (NG), alkaline phosphogypsum (PGA), and acid phosphogypsum (PGB). The materials were characterized physically and chemically, and Portland cement pastes were assessed by isothermal calorimetry, DRX, and TGA to identify the main hydrated products. Complementary compressive strength was evaluated in mortars. Furthermore, chemically soluble fluoride and phosphate contents were added to cement with NG, whose hydration was monitored by isothermal calorimetry. Portland cement with acid PG, soluble phosphates and fluorides presented hydration delays. However, soluble phosphates showed a more significant delay effect on cement than soluble fluorides. Cement setting times were extended with P2O5 soluble from 0.33% to 1.32%. Also, there is no relevant difference between the hydration products and compressive strength of alkaline PG cement and NG cement. Thus, the results suggest that low phosphate – fluoride and alkaline PGs may substitute NG in Portland cement.

Determination of natural radioactivity levels and radiation hazards for natural gypsum in Abay gorge, Dejen district, Ethiopia

ABSTRACT Natural gypsum has been studied as a building material, and it has been discovered that it is one of the potential sources of indoor radioactivity due to naturally occurring radioactive elements in it. The levels of radioactive elements obtained in natural gypsum available in Abay gorge Dejen district were accomplished by a well shielded and calibrated gamma spectrometry with high purity Ge detector to evaluate the radiation hazard to workers in Dejen gypsum factories and dwellers in buildings decorated with gypsum products. The results of this study revealed that radioactive elements 238U, 232Th, and 40K are found in raw gypsum samples, with specific activity ranging from 1.47 ± 0.26 to 2.42 ± 0.37 Bqkg−1, 1.10 ± 0.26 to 2.60 ± 0.48 Bqkg−1, and 4.27 ± 1.92 to 44.53 ± 2.84 Bqkg−1, respectively. The mean specific activities are 1.90 ± 0.33 Bqkg−1 for 238U, 1.99 ± 0.39 Bqkg−1 for 232Th, and 28.16 ± 2.57 Bqkg−1 for 40K, which are significantly lower than the intercontinental approved values. All of the calculated radioactive risk indices were significantly lower than the global recommended values for building materials. The values of various radioactive indices indicate that the use of gypsum powder obtained from studied samples in the construction of residences is considered safe.

RESISTANCE OF BASALT FIBRE IN THE ALKALINE ENVIRONMENT OF HYDRATING CEMENT SYSTEMS

The paper presents studies aimed at substantiating the possibility of using basalt fiber as dispersed reinforcement in cement systems based on expanding binders with high energy of expansion (stressing cements). Alkalinity resistance of basalt fiber by the accelerated method by a four-hour exposure in a saturated solution of Ca(OH)2 at temperature t=95°С, which allows simulating the operation process within 10 years in the environment of the cement stone, has been investigated. Tensile strength of cement samples with basalt fiber treated by the accelerated method has been proposed as one of the criteria for estimating the quality of alkali-resistant fiber. The application of NC on a Portland cement base and expanding additive consisting of a mixture of highly reactive metakaolin and natural gypsum allowing a decrease in pH of the medium from values ≈12.13 to ≈11.25 is an alternative way of reducing the alkalinity of hydrating medium as the most favorable for basalt fiber location. A number of experimental studies have been conducted to determine the strength properties and self-strains of basalt fiber-reinforced selfs-tressing cement. Experimental and theoretical studies have revealed that basalt fiber has high alkali resistance. The introduction of basalt fiber in an amount of 5% of the binder mass makes it possible to increase compressive strength of the SSC by 35%, tensile strength at bending by 68%, with self-strain corresponding to 0.22% of free expansion and 2.74 MPa of self-stressing, respectively.

Effect of Varying Levels of Sulphur and Sources on Sulphur Fractions in an Acid Alfisol of Himachal Pradesh

An investigation was conducted on cauliflower ( L. var. Palam Uphar) at CSK Himachal Pradesh KrishiBrassica oleracea Vishvavidyalaya, Palampur to study the effect of varying levels of sulphur and its Sources on various sulphur fractions in an Acid Alfisol of Himachal Pradesh. The experiment consisted of three levels (12.5, 25, 37.5 kg S ha ) and four sources (Sartaj natural gypsum, locally -1 available gypsum, elemental sulphur and single super phosphate) of sulphur. Available, water soluble, organic form of sulphur and total sulphur increased significantly with increased levels of sulphur. Whereas, in sources Sartaj gypsum recorded maximum available sulphur (12.4 mg kg ) and water soluble (9.8 mg kg ) followed by single super phosphate, locally available gypsum and elemental sulphur. Different -1 -1 sources of sulphur did not show any significant effect on heat soluble sulphur, organic sulphur and total sulphur. All sulphur fractions were significantly and positively correlated with available form of sulphur. However, highest correlation was observed with water soluble sulphur.

Recent Advances in Production of Ecofriendly Polylactide (PLA)-Calcium Sulfate (Anhydrite II) Composites: From the Evidence of Filler Stability to the Effects of PLA Matrix and Filling on Key Properties.

The melt–mixing of polylactide (PLA) with micro- and/or nanofillers is a key method used to obtain specific end-use characteristics and improvements of properties. So-called “insoluble” CaSO4 (CS) β-anhydrite II (AII) is a mineral filler recently considered for the industry of polymer composites. First, the study proves that AII made from natural gypsum by a specifically thermal treatment is highly stable compared to other CS forms. Then, PLAs of different isomer purity and molecular weights (for injection molding (IM) and extrusion), have been used to produce “green” composites filled with 20–40 wt.% AII. The composites show good thermal and mechanical properties, accounting for the excellent filler dispersion and stability. The stiffness of composites increases with the amount of filler, whereas their tensile strength is found to be dependent on PLA molecular weights. Interestingly, the impact resistance is improved by adding 20% AII into all investigated PLAs. Due to advanced kinetics of crystallization ascribed to the effects of AII and use of a PLA grade of high L-lactic acid isomer purity, the composites show after IM an impressive degree of crystallinity (DC), i.e., as high as 50%, while their Vicat softening temperature is remarkably increased to 160 °C, which are thermal properties of great interest for applications requiring elevated rigidity and heat resistance.

Mineral Paragenesis Precipitating in Salt Flat Pools of Continental Environments Replicated in Microbial Mat Microcosms without Evaporation

Mineral precipitation can be observed in natural environments, such as lagoons, rivers, springs, and soils. The primary precipitation process has long been believed to be abiotic due to evaporation, leading to phase supersaturation. However, biotic interactions of microbial metabolism, organic compounds, and dissolved ions leading to mineral precipitation has been shown in laboratory studies using single-organism culture. The increase in pH inducing calcium carbonate precipitation due to oxygenic photosynthesis by Cyanobacteria and the release of ions due to organic matter decomposition by Firmicutes-inducing magnesium carbonate precipitation are recognized examples. As microbes do not live as pure cultures in natural environments but form complex communities, such pure culture lab studies do not reflect natural conditions. In this study, we grew natural complex microbial communities in microcosm conditions using filtered brine as water column and two types of natural gypsum substrates, and we replenished incubations to avoid evaporation. We monitored microbial communities through optical microscopy and analyzed mineral paragenesis in association with and without microbes, using different analytical techniques, such X-ray diffraction, and optical and field emission scanning electron microscopies. To detect changes throughout the experiment, small amounts of water column brine were extracted for physicochemial determinations. We were able to detect mineral paragenesis, avoiding evaporation, including major phases of chemical sedimentary rocks, such as gypsum, calcium carbonate, and some silicates in association to microbes. In addition, we evidenced that the use of natural substrates positively impacts growth of microbial communities, promoting the development of more biomass. This study can be seen as the first attempt and proof of concept of differentiating biotic and abiotic participation in evaporitic deposits, as they can form mineral paragenesis without evaporation. Future studies with microcosm experiments using microbial mats will be needed to establish mineral precipitation induced by micro-organisms and their extracellular polymeric substances (EPS), specifically to replicate mineral paragenesis sedimented from natural brines.

Heavy metal pollution risk of desulfurized steel slag as a soil amendment in cycling use of solid wastes

The by-product of wet flue gas desulfurization, desulfurized steel slag (DS), had chemical characteristics like natural gypsum that can be used to improve saline-sodic soil. However, contamination risk of heavy metals for cycling utilization of DS in agriculture was concerned mostly. Both pot and field experiments were conducted for evaluating the potential pollution risk of DS as the amendment of saline-sodic soil. Results showed that application of DS decreased the contents of Cd, Cu, Zn, and Pb, while significantly increasing chromium (Cr) content in DS-amended soils. The field experiment demonstrated that the migration of heavy metals (Cd, Zn, Cu, and Pb) in the soil profile was negligible. The application of DS at the dosage of 22.5–225 tons/ha significantly increased the Cr content in alfalfa (Medicago sativa L.) but lower than the national standard for feed in China (GB 13078-2017). DS altered the chemical fraction of heavy metals (Zn, Cu, and Pb), transferred exchangeable, reducible into oxidizable and residual forms in DS-amended soil. Application of DS combined with fulvic acid (FA) could effectively reduce the movement of heavy metals in soil and the accumulation of Cr in alfalfa. Based on our results, DS was a safe and feasible material for agricultural use and presented relatively little pollution risk of heavy metals. However, the results also showed that DS to a certain extent had a potential environmental risk of Cr if larger dosages of DS were used.

Experimental Study and Mechanism Analysis of Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum with Dynamic Method.

Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum and crystal modifiers was approximately 18%, and the pH value was approximately 6.0. The mixture did not need to be pressed into bricks or made into slurry, and it was directly sent into the autoclave reactor for reaction. It was successfully applied to the practical production and application of FGD gypsum, citric acid gypsum and phosphogypsum. In this work, the compositions and morphology of the product at different stages of the reaction were examined and compared. In particular, single-crystal diffraction was used to produce the crystal structure of CaSO4·0.5H2O, and the results were as follows: a = 13.550(3); b = 13.855(3); c = 12.658(3); β = 117.79(3)°; space group C2. The preferential growth along the c-axis and the interaction mechanism between the carboxylate groups and the crystal were discussed throughout the analysis of the crystal structure.

Modification of phosphogypsum using circulating fluidized bed fly ash and carbide slag for use as cement retarder

Cement retarder preparation is one of the main avenues for the resource utilization of phosphogypsum, and appropriate modification technology is the key for ensuring that the phosphogypsum is adjusted for achieving the desired setting time. This study uses carbide slag, circulating fluidized bed (CFB) fly ash, and other solid wastes to comprehensively modify phosphogypsum required for preparing the cement retarder; in addition, it discusses the influence of material ratio and aging time on the modification effect of phosphogypsum. The effects of modified phosphogypsum, undisturbed phosphogypsum, and natural gypsum on the properties of Portland cement were comparatively studied. The modification mechanism of carbide slag and CFB fly ash on phosphogypsum and the mechanism of influence of the modified phosphogypsum on the hydration characteristics of Portland cement were revealed by XRD, SEM, and hydration heat analyses. The results show that adding 6% carbide slag and 4% CFB fly ash can effectively reduce the content of soluble phosphorus and soluble fluorine in phosphogypsum, increase the pH value, enhance the strength of modified phosphogypsum, and enable its use as a cement retarder after aging for 7 d. Compared with the undisturbed phosphogypsum, the setting time of Portland cement made from modified phosphogypsum is significantly shorter; the early-strength is higher, and the compatibility with water reducing agent is better. The microscopic test results showed that the CFB fly ash has good self-hardening properties. The CFB fly ash also showed better hydration hardening performance and curing effect on soluble phosphorus and soluble fluorine under the synergistic excitation of alkali-sulfur by carbide slag and phosphogypsum, which is beneficial for the modification of phosphogypsum and improves the retardation effect of Portland cement.

Closing the upcoming EU gypsum gap with phosphogypsum

Phosphogypsum (PG) is a residue from the fertilizer industry used by Portland cement companies as a source of calcium sulfate to control the setting time during the hydration (or hardening process). However, certain impurities can alter the cement hydration kinetics. Thus, this paper aims to analyze the soluble phosphate, fluoride, and pH effects of Brazilian phosphogypsum used as a setting retarder on the hydration of Portland cement. Different sources of calcium sulfate were analyzed: natural gypsum (NG), alkaline phosphogypsum (PGA), and acid phosphogypsum (PGB). The materials were characterized physically and chemically, and Portland cement pastes were assessed by isothermal calorimetry, DRX, and TGA to identify the main hydrated products. Complementary compressive strength was evaluated in mortars. Furthermore, chemically soluble fluoride and phosphate contents were added to cement with NG, whose hydration was monitored by isothermal calorimetry. Portland cement with acid PG, soluble phosphates and fluorides presented hydration delays. However, soluble phosphates showed a more significant delay effect on cement than soluble fluorides. Cement setting times were extended with P2O5 soluble from 0.33% to 1.32%. Also, there is no relevant difference between the hydration products and compressive strength of alkaline PG cement and NG cement. Thus, the results suggest that low phosphate – fluoride and alkaline PGs may substitute NG in Portland cement.

Influence of yellow gypsum on nutrient uptake and yield of groundnut in different acid soils of Southern India

Yellow gypsum (YG), a synthetic product from Linz-Donawitz slag containing high iron (Fe) (5.41%), zinc (Zn) (0.37%) and silicon (Si) (3.41%) can be used as a source of these nutrients along with calcium (Ca) and sulphur (S) for groundnut production. Three field experiments were conducted to know the effect of different rates (500 and 625 kg YG ha−1) and time of application (basal alone and basal + split) of YG on growth, yield and economic returns of groundnut, and micronutrient and Si availability and their uptake in comparison with basal application of 500 kg natural gypsum (NG) ha−1. Basal alone and basal + split application of YG significantly increased the growth, yield and economic returns of groundnut. Further, it increased the soil pH, availability of micronutrients, Si and their uptake by haulm and kernel of groundnut over NG. Irrespective of the location, YG application recorded higher plant available nutrient (PAN) coefficient of micronutrients, while NG application recorded higher PAN recovery coefficient of Si. Basal + split application of YG resulted in better growth and yield of groundnut than basal application of YG. In conclusion, YG can be a potential alternative for NG as a source of Fe, Zn and Si along with Ca and S for groundnut production.

Improvement mechanism of water resistance and volume stability of magnesium oxychloride cement: A comparison study on the influences of various gypsum

The development of magnesium oxychloride cement can effectively utilize the waste of potash industry and reduce its harm to the environment. Although magnesium oxychloride cement paste (MOCP) has excellent performance in dry environment, its performance is greatly deteriorated in water or humid environment, which severely limits its practical application. In order to improve the water resistance of MOCP, MOCP was modified by various gypsum in this study, and the intrinsic mechanism was explored. Results showed that replacing MgO with gypsum delayed the setting time of MOCP and effectively improved its volume stability. Although the incorporation of gypsum reduced the 14-d air-cured compressive strength of MOCP, waste gypsum was able to significantly improve the water resistance of MOCP compared to natural gypsum. When 80% flue gas desulfurization gypsum and phosphogypsum (weight of magnesium oxide) were incorporated into MOCP, the 14-d air-cured compressive strength of MOCP was only decreased by 14.49% and 15.94% compared with the control group, but its 28-d water immersion strength retention coefficient (SRC) could still reach 61.02% and 46.55%, respectively. However, for the control group and MOCP with 80% natural gypsum, the 28-d SRC were only 28.99% and 8.41%. The incorporation of high-volume waste gypsum to MOCP not only reduced the relative content of MgO, but also improved the stability of the 5-phase in water, which was beneficial to improve the water resistance of MOCP. In addition, high-volume waste gypsum-modified MOCP had lower cost and carbon emissions, and exhibited superior water resistance and sustainability compared to existing MOCP compositions.

Impacts of MgO waste:GGBS formulations on the performance of a stabilised natural high sulphate bearing soil

Industrial and urban wastes have been generated over time due to urban development with severe environmental and health implications. This paper reports the valorisation of waste and industrial by-product (magnesium oxide waste – MG1 and Ground Granulated Blast furnace Slag – GGBS) to develop an alternative cementitious binder for suppressing swelling in high sulphate bearing soils due to the formation of a highly expansive crystalline hydrate (ettringite) upon treatment with Portland Cement – PC or lime. Cylinder test specimens were developed using three MG1:GGBS proportions by weight (10:90, 20:80 and 30:70) to stabilise a natural Gypsum marl soil (GM) containing high levels of sulphate at varying stabiliser dosages (6, 8 and 10 wt%), with PC as the control binder. UCS, Linear Expansion and SEM investigations were employed to assess the engineering suitability of the MG1:GGBS stabilised GM cylinder test specimen. Results suggest the viability of producing an alternative cementitious binder using up to 30 wt% MgO-waste to successfully activate GGBS at stabiliser dosages of 6–10 wt%. From a mechanical perspective, the MG1:GGBS stabilised GM soil was 1.5–3 times more than the control at 28 days moist curing age, while the resistance to linear expansion produced near-zero swellings (0.13%–0.2%) after 56 days, in comparison with the control of 3.2%. SEM micrographs showed a more compact structure with lesser voids and no morphology of ettringite. This new technology is expected to mitigate the environmental concerns of using PC and promote sustainable techniques of reusing industrial by-product materials for stabilising sulphate soils.

Flotation separation of quartz from gypsum using benzyl quaternary ammonium salt as collector

Phosphogypsum is a kind of industrial by-product, which could be used as building materials instead of natural gypsum after removing impurities. Flotation is an effective method to remove the silicon-containing impurity quartz in the phosphogypsum. In this work, a surfactant tetradecyl dimethyl benzyl ammonium chloride (TDBAC) was first used as the collector of quartz to be separated from gypsum. The flotation behaviors of quartz and gypsum were investigated by micro-flotation experiments. The flotation mechanisms were analyzed through Zeta potential testing, Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Micro-flotation results show that TDBAC exhibited outstanding collecting capacity and selectivity for quartz over the wide pH range of 2.5–9.5. FTIR results declared that TDBAC could be successfully adsorbed on the surface quartz. The analysis results of zeta potential and XPS indicate that the interaction mechanisms of TDBAC with quartz were involved electrostatic attraction and hydrogen-bond interaction, whereas the adsorption onto gypsum surface was only by the weak electrostatic attraction and hydrogen-bond interaction. The results of this work showed that TDBAC is expected to be an effective collector of quartz for removing silicon impurity from the industrial phosphogypsum.

Faience Waste for the Production of Wall Products.

Increasing the efficiency of using gypsum binders can be carried out by using not natural gypsum raw materials, but calcium sulfate-containing waste from various industries (phosphogypsum, borogypsum, citrogypsum, etc.). As the main source material in the work, we used gypsum-containing waste from a faience factory in the form of waste molds for casting dishes, souvenirs and plumbing fixtures. It has been established that the optimal binding system is formed by mixing powders of dihydrate technogenic gypsum from a coarse and fine earthenware factory with average particle diameters of 3.473 microns and 3.065 microns in a percentage ratio of 30:70, respectively. Using a computer software developed by the authors, which makes it possible to simulate the microstructure of a raw mixture taking into account the contact interaction of particles and calculate the average coordination number, models of binary packing of particles were constructed at various ratios of their diameters. Studies of the strength of composites obtained on the basis of bidisperse systems have shown the presence of an extremum in the region of mixtures containing 30% coarse powder. With optimal packing, a large number of phase contacts are formed due to the regulation of the grain composition of the bidisperse system. It was revealed that a brick based on the waste of two-water gypsum from earthenware production has 2.5–5 times better characteristics of compressive strength than traditional building wall products based on natural gypsum. At the same time, the strength immediately after molding is more than 3 times higher than that of traditional gypsum products. Even higher indicators are achieved when adding microcalcite in addition to the waste of earthenware production, in this case, the compressive strength is 3–6 times higher, and the strength immediately after molding is almost 3 times higher than that of traditional gypsum products.

Transformation of flue gas desulfurization (FGD) gypsum to β-CaSO4·0.5H2O whiskers using facile water treatment

A novel way for transformation of flue gas desulfurization (FGD) gypsum, an industrial by-product to β-CaSO4·0.5H2O whiskers is investigated for calcium sulfate rich alternative construction material. As the consumption of gypsum products is increasing in construction industry and limited amount of natural gypsum is available, herein facile water treatment is used to generate fine tubular particles by recrystallization and growth of β-CaSO4·0.5H2O without any chemical for the first time. Remarkable properties of FGD gypsum are characterized with mean particle size of 42.875–48.759 µm, bulk density of 1.08–1.21 g/cm3 and specific gravity of 3.06–3.35. XRD, FTIR, WD-XRF, FESEM-EDS and HR-TEM analysis confirm the composition and morphology of the synthesized material. XRD pattern of treated FGD gypsum confirms the presence of highly crystalline β-CaSO4·0.5H2O. FESEM micrographs confirm the micro-needle type morphology with very high aspect ratio of 25:1.Results showed that magnetic stirring improves the removal efficacy of impurities. This study will open the perspective for development of FGD gypsum whiskers with very high aspect ratio and will pave the way for future investigation for a green alternate of natural gypsum for construction applications.