Recovery of zinc and extraction of calcium and sulfur from zinc-rich gypsum residue by selective reduction roasting combined with hydrolysis

A novel process that includes selective reduction roasting followed by hydrolysis was proposed in this work to recover zinc, and efficiently extract calcium and sulfur from hazardous zinc-rich gypsum residue (ZGR) waste for high-purity of CaCO₃ and sulfur production. The selective reduction behaviors of ZGR during the reduction roasting were investigated in detail based on thermodynamic analysis and roasting experiments. The effect of roasting temperature, carbon dosage and time on the selective reduction of ZGR was comprehensively investigated, and the results indicated that ZnO and CaSO₄ in the ZGR can be selectively reduced to Zn(g) and CaS, respectively. The volatile Zn(g) was oxidized to ZnO and enriched in the dust, which can be used as a secondary zinc resource. Moreover, the hydrolysis behaviors and leaching kinetic of CaS during hydrolysis were studied intensively. Results depicted that in the H₂S-H₂O system, the CaS in the roasted product can be selectively and efficiently dissolved into the leachate. Furthermore, the kinetic analysis revealed that the hydrolysis of CaS conformed to the internal diffusion reaction control model in the shrinking core model and the apparent activation energy Ea = -12.02 kJ/mol. The obtained hydrolysate with low impurities could be used to capture CO₂ for the production of high-purity sulfur and CaCO₃. Iron and other impurities in the roasted product were concentrated into the leaching slag in the form of metallic iron and akermanite. The whole process realized the recovery of zinc, and the selective and effective extraction of calcium and sulfur, which could provide an alternative process for the large-scale treatment of these hazardous wastes.

Continuous and simultaneous conversion of phosphogypsum waste to sodium sulfate and potassium sulfate using quaternary phase diagram

In this present work, the transformation of the Moroccan phosphogypsum (PG) waste, considered a potential source of sulfate, into potassium sulfate compound could help reduce environmental impact and create a new value chain for the phosphate industry. Generally, solid-liquid equilibria are frequently applied in chemical industries. They are a valuable aid in visualizing the precipitation, separation, and purification of a solid phase and the pathways by which crystallization can occur. This process aims to produce potassium sulfate (K₂SO₄), a high-value fertilizer, from sulfate solutions obtained after dissolving PG in a NaOH medium. The quaternary phase diagram Na⁺, K⁺//Cl^-, SO₄^2--H₂O at 25 °C was especially used to determine the operating conditions and the design of a crystallization process during the PG conversion into K₂SO₄. The Jänecke representation of this system enables the determination of the optimal trajectory in the phase diagram for the double decomposition reaction. X-ray fluorescent (XRF) and X-ray diffraction (XRD) techniques were conducted to identify the crystalline phases formed during our process. In summary, the results of this study could contribute to the development of a sustainable valorization PG. Furthermore, K₂SO₄ represents a good alternative to potassium chloride for chloride-sensitive crops.

A multi-analytical evaluation of the depositional pattern on open-air rock art panels at "Abrigo del Lince" (Badajoz, Spain)

Microscopic observation correlated with chemical-mineralogical characterization was performed on pigment samples from "Abrigo del Lince" rock art site (V-IV millennium BC), in order to provide contributions to the study of prehistoric schematic art on granite in the province of Badajoz (Spain). The research objectives include the understanding of technological and cultural aspects, as well as of conservation and deterioration issues related to the pictographs. The multi-analytical approach encompasses the integration of microscopic observation, SEM-EDS analysis, micro-Raman spectroscopy, and ATR-FTIR and allowed to achieve a multispectral overview of the samples and to describe their varied composition and the alteration pattern which connects them. The main phases overlying the granitic bedrock and involved in this sequence are as follows: hematite, whewellite, and gypsum. While hematite could be stratigraphically considered the most ancient layer and assigned to the use of red ochre as a pigment, whewellite and gypsum are the main constituent of the alteration layer which forms a patina over the pictographs, due to weathering processes. Finally, the role of biofilms in rock art conservation is discussed, suggesting that, especially for what concern thin and homogenous layers of oxalates, their presence should not be necessarily considered an issue.

Irrigation water quality, gypsum, and city waste compost addition affect P dynamics in saline-sodic soils

The amendments used for sodicity reclamation also profoundly influence P dynamics and leaching losses. This study characterized the effect of irrigation water quality on P dynamics and leaching from saline-sodic soil during reclamation utilizing gypsum alone or in combination with manure and city compost. Changes in properties of unleached and leached soils were fitted with labile P pools using redundancy analysis. The relation between leachate properties and P loss was explained by means of monitoring leachate properties up to ten pore volumes. During incubation, the water-extractable P (P_H2O) concentration was greater than Olsen's P (P_NaHCO3) in all treatments. The P_NaHCO3 decreased in proportion to the amount of gypsum applied. Applying the organics with gypsum increased the P_NaHCO3, P_H2O, and organic P concentration compared to gypsum alone. The labile P pools in soil were positively correlated with HCO₃^- content (r = 0.39-0.77; P < 0.05) of leached and unleached soils. Adding gypsum and compost caused a 10-14% decrease in cumulative P leaching. The cumulative P leaching were greater with rainwater compared to saline water of SAR (sodium adsorption ratio) 5 and 15. The CO₃^2-, HCO₃^-, pH, and SO₄^2-content of the leachate explained about 71% variability in total P leaching (adj. R² = 0.71; P < 0.001). This study concludes that low electrolyte water had a greater risk of P leaching and associated environmental pollution. Leaching of the saline-sodic soil amended with gypsum and city waste compost with low SAR saline water can reduce P leaching compared to good quality rainwater.

A novel and sustainable approach for biotransformation of phosphogypsum to calcium carbonate using urease producing Lysinibacillus sphaericus strain GUMP2

Phosphogypsum (CaSO₄) is produced as a waste by-product during phosphoric acid production in the fertilizer industry. Only 15% of worldwide phosphogypsum production is recycled, while 85% is stored in the vicinity of factories as huge piles resulting in environmental and health hazards. An extensively studied biotransformation of phosphogypsum to calcium carbonate or calcite (CaCO₃) using sulfate reducing bacteria (SRBs) is a prolonged process and results in the formation of extremely hazardous H₂S gas. Here we report for the first time a novel approach for biotransformation of phosphogypsum to CaCO₃ using urease producing Lysinibacillus sphaericus strain GUMP2. The strain could effectively transform phosphogypsum to crystalline, bead-shaped CaCO₃ precipitates. In a batch reactor with the PG loading rate of 60 g/L, 100% biotransformation was observed within seven days. After calcite recovery, the ammonium sulfate formed in the supernatant was recovered by precipitation. Urease-producing L. sphaericus strain GUMP2 could be used to remove the hazardous phosphogypsum from the environment by converting it to the industrially useful CaCO₃ and ammonium sulfate, a valuable agricultural fertilizer. This novel and sustainable approach could be a promising solution for the hazardous phosphogypsum in the phosphoric acid industries.

Identification of mercury species in coal combustion by-products from power plants using thermal desorption-atomic fluorescence spectrometry on-line coupling system

Along with the environmental protection policies becoming strict in China, the air pollution control devices (especially selective catalytic reduction (SCR)) are widely equipped in coal-fired power plants. The installation and run of these devices will inevitably affect mercury (Hg) species distribution in coal fired by-products such like fly ash (FA) and gypsum. In this work, a new on-line coupling system based on atomic fluorescence spectrometry (AFS) with a home-made chromatographic workstation was successfully developed to identify Hg species through thermal programmed desorption (TPD). The influences of matrix, furnace temperature, and carrier gas flow on analytical performance were investigated and the parameters were optimized. The FA and gypsum samples from coal-fired power plants equipped with SCR were collected and the mercury species were analyzed by the developed coupling system. HgCl₂ and HgO were the main species in FA, while Hg₂Cl₂ and HgO were the main species in gypsum. All of Hg species in the studied FA and gypsum samples were released below 400 °C. A sequential extraction procedure was applied to further verify the operational Hg species including mobile and non-mobile fractions in FA and gypsum samples. This study demonstrated that AFS coupled with TPD procedure was an effective method to analyze Hg species in coal combustion by-products from power plants.

Interplay between abiotic and microbial biofilm-mediated processes for travertine formation: Insights from a thermal spring (Piscine Carletti, Viterbo, Italy)

Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO₂ degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur-oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S-oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals.

Gypsum scale formation and inhibition kinetics with implications in membrane system

Water desalination using membrane technology is one of the main technologies to resolve water pollution and scarcity issues. In the membrane treatment process, mineral scale deposition and fouling is a severe challenge that can lead to filtration efficiency decrease, permeate quality compromise, and even membrane damage. Multiple methods have been developed to resolve this problem, such as scale inhibitor addition, product recovery ratio adjustment, periodic membrane surface flushing. The performance of these methods largely depends on the ability to accurately predict the kinetics of mineral scale deposition and fouling with or without inhibitors. Gypsum is one of the most common and troublesome inorganic mineral scales in membrane systems, however, no mechanistic model is available to accurately predict the induction time of gypsum crystallization and inhibition. In this study, a new gypsum crystallization and inhibition model based on the classical nucleation theory and a Langmuir type adsorption isotherm has been developed. Through this model, it is believed that gypsum nucleation may gradually transit from homogeneous to heterogeneous nucleation when the gypsum saturation index (SI) decreases. Such transition is represented by a gradual decrease of surface tension at smaller SI values. This model assumes that the adsorption of inhibitors onto the gypsum nucleus can increase the nucleus superficial surface tension and prolong the induction time. Using the new model, this study accurately predicted the gypsum crystallization induction times with or without nine commonly used scale inhibitors over wide ranges of temperature (25-90 °C), SI (0.04-0.96), and background NaCl concentration (0-6 mol/L). The fitted affinity constants between scale inhibitors and gypsum show a good correlation with those between the same inhibitors and barite, indicating a similar inhibition mechanism via adsorption. Furthermore, by incorporating this model with the two-phase mineral deposition model our group developed previously, this study accurately predicts the gypsum deposition time on the membrane material surfaces reported in the literature. We believe that the model developed in this study can not only accurately predict the gypsum crystallization induction time with or without scale inhibitors, elucidate the gypsum crystallization and inhibition mechanisms, but also optimize the mineral scale control in the membrane filtration system.

Flotation purification of waste high-silica phosphogypsum

High-silica phosphogypsum (PG) is a kind of industrial by-product with great utilization potential. However, it is difficult to reuse PG directly due to the related gangue minerals (e.g., SiO₂), and thus efficient purification is required to allow its further applications. Herein, a typical high-silica phosphogypsum waste was purified by a new "reverse-direct flotation" method. The organic matters and fine slimes were removed by reverse flotation, and then, the silica impurity was removed by direct flotation. Via the closed-circuit flotation process, the whiteness of the PG concentrate is improved from 33.23 to 63.42, and the purity of gypsum in the PG concentrate increases from 83.90% to 96.70%, with a gypsum recovery of 85%. Additionally, the content of SiO₂ is significantly reduced from 11.11% to 0.07%. In-depth investigations suggest that the difference in the floatability of gypsum and quartz is prominently intensified by flotation reagents at pH = 2-2.5, and thus leads to good desilication performance. Further characteristics of the PG concentrate prove that impurities have been well removed, and the PG concentrate meets the requirement of related standards for gypsum building materials. The flotation method reported here paves the way for the purification of high-silica phosphogypsum, which can be extended to the purification and value-added reutilization of other industrial solid wastes.

Concentrations, Speciation, and Potential Release of Hazardous Heavy Metals from the Solid Combustion Residues of Coal-Fired Power Plants

Hazardous heavy metal-laden coal combustion byproducts exposed to precipitation or surface/groundwater are of environmental concern. This study analyzed fly ash (FA) and desulfurization gypsum (FGD gypsum) samples obtained from 16 coal-fired power plants in Guizhou Province, China. A combination of field and laboratory studies was used to investigate the binding forms of lead (Pb), cadmium (Cd), and chromium (Cr) and their leaching characteristics under natural storage conditions. The results showed that there were significant proportions of residual states of these elements in FA (84-99% for Pb, 83-91% for Cd, and 73-97% for Cr), indicating a lack of migration to other environmental media. FGD gypsum contained high proportions of metals in migratable states, but the environmental risks were low due to their very low concentrations. The release of Pb, Cd, and Cr from FA and FGD gypsum into extracts varied according to pH. This is related to the form of each element in the solid and the series of reactions that occurs during the leaching process. However, aside from Cr in FA, all heavy metals in FA and FGD gypsum samples were present in concentrations below the relevant standards for landfill leachate, indicating very low release rates. The Cr levels (206-273 μg/L) in some of the FA extracts were higher than the limits for water pollution from domestic landfill, indicating that Cr in FA poses a leaching risk. The results of field leachate sampling and indoor simulated rainfall experiments further validated these findings, indicating that the release of Cr from stockpiled coal FA is a cause for concern.

A new injectable quick hardening anti-collapse bone cement allows for improving biodegradation and bone repair

The development of injectable cement-like biomaterials via a minimally invasive approach has always attracted considerable clinical interest for modern bone regeneration and repair. Although α-tricalcium phosphate (α-TCP) powders may readily react with water to form hydraulic calcium-deficient hydroxyapatite (CDHA) cement, its long setting time, poor anti-collapse properties, and low biodegradability are suboptimal for a variety of clinical applications. This study aimed to develop new injectable α-TCP-based bone cements via strontium doping, α-calcium sulfate hemihydrate (CSH) addition and liquid phase optimization. A combination of citric acid and chitosan was identified to facilitate the injectable and anti-washout properties, enabling higher resistance to structure collapse. Furthermore, CSH addition (5 %-15 %) was favorable for shortening the setting time (5-20 min) and maintaining the compressive strength (10-14 MPa) during incubation in an aqueous buffer medium. These α-TCP-based composites could also accelerate the biodegradation rate and new bone regeneration in rabbit lateral femoral bone defect models in vivo. Our studies demonstrate that foreign ion doping, secondary phase addition and liquid medium optimization could synergistically improve the physicochemical properties and biological performance of α-TCP-based bone cements, which will be promising biomaterials for repairing bone defects in situations of trauma and diseased bone.

Hypercalcaemia caused by calcium sulfate beads

Hypercalcaemia is a relatively common metabolic disturbance seen in hospitalised patients; however, given the complicated systems of calcium regulation, it can take a significant amount of time and testing to pinpoint the aetiology. This case discusses a patient who developed acute hypercalcaemia from calcium sulfate-containing antibiotic beads placed during an orthopaedic procedure. These beads are used in surgical procedures to fill gaps/voids in bony structures and for local delivery of antibiotics. The case highlights the importance of careful review of a patient's hospital course, including the administration of medical products that may not be clearly documented on a patient's medicine administration record when working up an unexplained finding.

Characteristic pollutant purification analysis of modified phosphogypsum comprehensive utilization

The waste product phosphogypsum (PG) is produced in phosphoric acid production processes. Its storage requires large amounts of land resources and poses serious environmental risks. In this work, detailed experimental research was carried out to investigate the potential reuse of PG after calcination modification as a novel building material for cast-in-place concrete products. The calcination modification mechanism was studied, and the environmental risk assessment of modified PG was presented. The results showed that the calcination modification includes crystal phase transformation, removal of impurities, and modifying the pH value. The calcination was carried out at 280 °C for 5 h, where the resulting product was a pH value of 7.1, and the soluble fluorine and phosphorus removal rates reached up to 69.2% and 71.2%, respectively. These removal rates met the requirements of the China national standard Phosphogypsum (GB/T 23456-2018). To ensure the environmental safety, ecological risk assessment methods for determining the leaching toxicity of the modified PG were employed. The toxicity of Ba and P elements in the modified PG products was assessed, as well as the leaching toxicity concentrations of all particular heavy metals, which were found well below the limits set by the national standards. All the results presented strongly suggest that the 280 °C modified PG presented here has excellent application potential as a raw component in building materials.

Potential uses of phosphogypsum: A review

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industry that is produced during the phosphoric acid production process. Annual global PG production ranges between 100 to 300 Mt, with only 15% of that utilized while the rest is usually placed on large dumps with potential serious human and environmental impacts. The aim of this study is to give an overview and to evaluate the existing and potential uses of PG that extend from soil stabilization to cement and chemical industry and for agricultural to geotechnical, human impacts, and environmental applications. More specifically, PG can be used as a substitute in the cement industry, in building materials and in road construction, as a fertilizer for soil improvement, as a raw material for the production of some chemicals, and as a backfilling material for the rehabilitation of abandoned mines and quarries, while the recovery of gypsum and the extraction of rare earth elements signifies the potential importance of PG to cyclic economy. The paper offers an extensive overview of existing and potential uses of PG, discusses their adequacy, and reveals that PG can be widely used under certain conditions, rather than disposed as waste in stockpiles.

Utilization path of bulk industrial solid waste: A review on the multi-directional resource utilization path of phosphogypsum

Phosphogypsum is one of the hottest issues in the field of environmental solid waste treatment, with complex and changeable composition. Meanwhile, phosphogypsum contains a large number of impurities, thus leading to the low resource utilization rate, and it can only be stockpiled in large quantities. Phosphogypsum occupies a lot of land and poses a serious pollution threat to the ecological environment. This paper mainly summarizes the existing pretreatment and resource utilization technology of phosphogypsum. The pretreatment mainly includes dry method and wet method. The resource utilization technology mainly includes building materials, chemical raw materials, agriculture, environmental functional materials, filling materials, carbon sequestration and rare and precious extraction. Although there are many aspects of resource utilization of phosphogypsum, the existing technology is far from being able to consume a large amount of accumulated and generated phosphogypsum. Through the analysis, the comparison and mechanism analysis of the existing multifaceted and multi-level resource treatment technologies of phosphogypsum, the four promising resource utilization directions of phosphogypsum are put forward, mainly including prefabricated building materials, eco-friendly materials and soil materials, and new green functional materials and chemical fillers. Moreover, this paper summarizes the research basis of multi field and all-round treatment and disposal of phosphogypsum, which reduces repeated researches and development, as well as the treatment cost of phosphogypsum. This paper could provide a feasible research direction for the resource treatment technology of phosphogypsum in the future, so as to improve the consumption of phosphogypsum and reduce environmental risks.

Management of solid waste marble powder: improving quality of sodium chloride obtained from sulphate-rich lake/subsoil brines with simultaneous recovery of high-purity gypsum and magnesium carbonate hydrate

Marble industry worldwide produces large amount of non-degradable marble dust powder (MDP) waste during mining and processing stages. MDP mainly comprises of CaCO₃ with small amounts of Mg, Fe or Si in various forms. In India, mainly in Rajasthan state, marble is quarried in huge amounts and MDP thus produced is collected improperly and dumped at any abandoned land or identified disposal sites. On the other hand, the composition of sub soil/lake brines of Rajasthan is typical in nature as it does not have much Ca²⁺ and Mg²⁺ impurities but contains higher levels of SO₄^2-. Therefore, the common salt (NaCl) produced from such brines is contaminated with Na₂SO₄ (8-30 wt%) depending upon SO₄^2- concentration in the brine. Such a salt produced is suitable neither for edible purpose nor for industrial usage. Herein, we have reacted MDP with HCl, and the resulting solution (CaCl₂ and MgCl₂ slurry) is used in stoichiometric ratio of Ca²⁺ to SO₄^2- in brines to produce high-purity NaCl and gypsum (CaSO₄·2H₂O) via fractional crystallization. Remaining magnesium-containing solution was reacted with Na₂CO₃ to prepare high purity magnesium carbonate hydrate. Purity of crystallized NaCl, CaSO₄·2H₂O and MgCO₃·6H₂O has been ascertained through analytical and spectral methods (TGA, FTIR, P-XRD). Field emission scanning electron microscopy was used to elucidate morphology of crystals. The method reported for improving purity of NaCl along with CaSO₄·2H₂O and MgCO₃·6H₂O production from sulphate-rich brines is simple and economic, and allows management of MDP generated in huge amounts, which poses problems of disposal.

Electron Paramagnetic Resonance and Synchrotron X-ray Absorption Spectroscopy for Highly Sensitive Characterization of Calcium Arsenates

Calcium arsenates such as pharmacolite (CaHAsO₄·2H₂O), haidingerite (CaHAsO₄·H₂O), and weilite (CaHAsO₄) are important sinks for arsenic in mine tailings as well as other natural and contaminated sites and are useful for reducing the mobility and bioavailability of this toxic metalloid in the environment. However, calcium arsenates usually occur in trace amounts dominated by other phases, making their detection, identification, and quantification challenging. In this contribution, pharmacolite, haidingerite, and weilite are shown to exhibit subtle but distinct postedge differences in As K-edge X-ray absorption near-edge structure (XANES) spectra and feature characteristic [AsO₃]^2-, [AsO₄]^2-, and [AsO₄]^4- radicals, all derived from the diamagnetic [HAsO₄]^2- precursor during γ-ray irradiation, in electron paramagnetic resonance (EPR) spectra. In particular, the ⁷⁵As (nuclear spin I = 3/2 and natural isotope abundance = 100%) hyperfine coupling constants of the [AsO₃]^2- radicals in pharmacolite and haidingerite as well as other minerals (e.g., calcite and gypsum) are clearly distinct, allowing the unambiguous identification of calcium arsenates by the EPR technique readily at ∼0.1 wt %. Similarly, linear combination fittings of As K-edge XANES spectra demonstrate that pharmacolite and haidingerite at ∼0.1 wt % each in gypsum-rich mixtures can be detected and quantified as well. Therefore, a combination of the EPR and XANES techniques is a powerful approach for the highly sensitive characterization of calcium arsenates in the quest for the safe management and remediation of arsenic contamination. This work demonstrates the highly sensitive characterization of calcium arsenates by integrated electron paramagnetic resonance and synchrotron X-ray absorption spectroscopy.

Transformation from calcium sulfate to calcium phosphate in biological environment

The formation of a nano-apatite surface layer is frequently considered a measure of bioactivity, especially for non-phosphate bioceramics. In the present study, strontium-doped calcium sulfate, (Ca,Sr)SO₄, was used to verify the feasibility of this measure. The (Ca,Sr)SO₄ specimen was prepared by mixing 10% SrSO₄ by weight with 90% CaSO₄·½H₂O powder by weight. A solid solution of (Ca,7.6%Sr)SO₄ was then produced by heating the powder mixture at 1100 °C for 1 h. The resulting (Ca,Sr)SO₄ specimen was readily degradable in phosphate solution. A newly formed surface layer in the form of flakes was formed within one day of specimen immersion in phosphate solution. Structural and microstructure-compositional analyses indicated that the flakes were composed of octacalcium phosphate (OCP) crystals. An amorphous interface containing OCP nanocrystals was found between the newly formed surface layer and the remaining (Ca,Sr)SO₄ specimen. The specimen was also implanted into a rat distal femur bone defect. In addition to new bone, fibrous tissue and inflammatory cells were found to interlace the (Ca,Sr)SO₄ specimen. The present study indicated that a more comprehensive evaluation is needed to assess the bioactivity of non-phosphate bioceramics. The newly formed surface layer on the (Ca,Sr)SO₄ specimen after soaking in phosphate solution for 28 days.

Long-term in vitro degradation and in vivo evaluation of resorbable bioceramics

An essential criterion for the selection of resorbable bioceramics is their ability to degrade inside human body within a reasonable time frame. Furthermore, if the bioceramic can release beneficial ions, such as strontium, as it degrades, recovery time might be shortened. The present study demonstrates that strontium-containing calcium sulfate (Sr,Ca)SO₄ can fulfill these criteria. A long-term in vitro degradation analysis for 12 weeks using sintered (Sr,Ca)SO₄ discs in phosphate buffered solution (PBS) was conducted. The sintered (Sr,Ca)SO₄ disc was then implanted into defects in the distal femur of rats. The degradation rate of (Sr,Ca)SO₄ discs showed a strong dependence on the Sr content. Similar results were observed between the long-term in vitro degradation analysis and the in vivo evaluation. The sintered (3.8%Sr,Ca)SO₄ disc lost more than 80% of its initial weight after soaking in PBS with shaking at 37 °C for 12 weeks. After 12 weeks in vivo, the remaining volume of the (3.8%Sr,Ca)SO₄ disc within the bone defect was ~25%. Over the same time period, new bone was formed at a relative volume of 40%. This study demonstrates the potential of (Sr,Ca)SO₄ bioceramic, and the benefits of using a long-term degradation test during the evaluation of resorbable bioceramics.

Evaluation of bioabsorbable calcium sulfate hemihydrate beads for local delivery of carboplatin

The objectives of this study were to evaluate a novel kit of resorbable calcium sulfate beads marketed specifically for use in veterinary medicine and generally used for local delivery of antimicrobials as carboplatin-delivery system. The study characterized the elution of carboplatin in vitro, and investigated whether the initial dose and formulation of carboplatin, or the bead size significantly influences carboplatin elution in vitro. Calcium sulfate hemihydrate beads of 3- and 5-mm diameter were prepared. Five doses and two formulations of carboplatin (20, 50, 100, and 500 mg carboplatin per kit in powder formulation; 20 mg in liquid formulation) were tested in triplicates for each diameter beads. Beads were placed in 37°C phosphate buffered saline for 72 hours. Carboplatin concentrations in the eluent were measured by high-performance liquid chromatography at 11 time points with a modified United States Pharmacopeia assay. Concentrations of carboplatin in the eluent proportionally increased with the initial dose and peaked between 13 and 52 hours, ranging from 42.1% to 79.3% of the incorporated load. Higher peak concentrations, percentages released, and elution rates were observed with the liquid formulation and with higher carboplatin doses. There was no significant difference in maximum carboplatin concentrations between 3- and 5-mm diameter beads, but 5-mm diameter beads had slower elution rates. The novel kit can be used for preparation of carboplatin-impregnated resorbable calcium sulfate beads at variable doses, sizes and formulations. Further study is warranted to define the in vivo requirements and effective carboplatin dose, spatial diffusion and desired duration of elution.

The effects of oyster shell/alpha-calcium sulfate hemihydrate/platelet-rich plasma/bone mesenchymal stem cells bioengineering scaffold on rat critical-sized calvarial defects

Engineering scaffolds combining natural biomineral and artificially synthesized material hold promising potential for bone tissue regeneration. We fabricated a bioengineering scaffold, oyster shell (OS) and alpha-calcium sulfate hemihydrate (α-CSH) as scaffold, platelet-rich plasma (PRP) as provider of growth factors and bone mesenchymal stem cells (BMSCs) as seed cells, and determined it could be applied as a new type of bone graft substitutes by rat calvarial defects repairing experiment in vitro and in vivo. SEM showed that the mean diameter of the pores was about 150 μm with a range of 50-200 μm, and scaffold's porosity was ~27.4% by Archimedes' Principle. In vitro, Scaffold + BMSCs + PRP group presented a higher ALP activity compared with other groups by ELISA (P < 0.05). But the expression of OC was not detectable on day 4 or 8. The MTT assay showed that the relative cell number of BMSCs+PRP group increased significantly (P < 0.05). In vivo, the smallest defect area of skull and highest volume of regenerated new bone were observed in Scaffold + PRP + BMSCs group by X-ray and Micro-CT analysis (P < 0.05). And the similar results also were observed in HE and Masson staining. The immunohistochemistry staining for osteogenic marker proteins ALP and OC showed that the most obvious positive staining was observed in Scaffold + PRP + BMSCs group (P < 0.05). The expression of inflammatory markers IL-6 and TNF-α was the lowest in control group (P < 0.05). In conclusion, a bioengineering scaffold based on OS, created by simply combining α-CSH and PRP and implanting with BMSCs, could be clinically useful and has marked advantages as a targeted, off-the-shelf, cell-loaded treatment option for the bone healing of critical-size calvarial defects.

Nanominerals assemblages and hazardous elements assessment in phosphogypsum from an abandoned phosphate fertilizer industry

The present work investigates hazardous elements and nanomineralogical assemblages of phosphogypsum waste from an abandoned phosphate fertilizer industry located in Santa Catarina state (Brazil). Correlations between the chemical composition, nanominerals, and ultrafine particles are discussed. Multifaceted physical-geochemical study provided a careful understanding of the nanomineralogical assemblage of the phosphogypsum waste. The electron beam investigation revealed the presence of many hazardous elements in the ultrafine particles. Cr, Pb, Mn, Se, Sr, and Zr, among others, were found in individual ultrafine particles and nanominerals in all studied samples. Besides that, rare earth elements were found in different concentration ranges, being Ce, La, and Nd, the rare earth elements, found in the higher concentrations, above 900 mg kg^-1. The data supplied by this article are important to characterize the phosphogypsum waste, assessing the potential hazard to the environment and human health, and also, provides information to enable the designing of alternatives to manage this waste.

Influence of time, temperature and humidity on the accuracy of alginate impressions

BACKGROUND

The goal of the current in vitro study was to assess the dimensional accuracy of dental impressions when stored at different times, temperature and humidity.

METHODS

Impressions were poured to an aluminium triangular die and three teeth placed at the three corners of the die. A total of 130 impressions were made, in which 10 were poured immediately following manufacturers' instructions and the remaining 120 specimens were divided into two groups on the basis of relative humidity during storage. Group-1: 100%, Group-2: 50% relative humidity. Impression was poured with type IV gypsum. The below points were chosen to determine the length between in each of the specimens using the traveling microscope with 10x magnifications after 24 hours of model recovery for calculating the effect of changes in storage conditions- relative humidity, temperature and delay in pouring the impressions, on dimensional accuracy.

RESULTS

Analysis of the results revealed that the casts achieved by pouring alginate impressions without delay were most accurate than the delay pouring. With the increase in temperature and time, the distance between the points increased and the casts obtained were bigger.

CONCLUSION

Irreversible hydrocolloids should be poured immediately for optimum dimensional stability.

Effects of increasing concentrations of unamended and gypsum modified bauxite residues on soil microbial community functions and structure - A mesocosm study

Bauxite residues (BR), commonly named red muds, are the saline-sodic waste produced during the extraction of alumina from bauxite. In this study, four kinds of BR were mixed at increasing concentrations with two soils in a mesososm experiment. Unamended BR from Provence (PRO) and Guinea (GUI) bauxite were selected, and Modified Bauxite Residues from PRO and GUI (MBR-PRO and MBR-GUI) were obtained by gypsum application and repeated leaching, in order to reduce their pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP). Several indicators of microbial community functions and structure (growth of culturable bacteria; enzymatic activities; C-sourced substrates degradation (Biolog®); bacteria and fungi PCR-RFLP fingerprints) were measured after 35 days of incubation. Results showed that PRO residue had stronger negative effects than GUI on all the tested indicators. Residues modified by gypsum addition (MBR-PRO, MBR-GUI) were equally or sometimes less harmful compared to unamended residues. Microbial activities (bacterial growth and enzyme activities) were more inhibited than the diversity of microbial functions (Biolog®), and the structure of bacterial and fungal communities was not affected by increasing concentrations of bauxite residues. EC and ESP were the main factors explaining the inhibition of microbial activities, although the origin of bauxite residue is of great importance too.

Distribution behavior of arsenate into α-calcium sulfate hemihydrate transformed from gypsum in solution

Transforming gypsum into α-calcium sulfate hemihydrate (α-HH) provides a promising utilization pathway for the abundant amount of chemical gypsum. The transformation follows the route of "dissolution-recrystallization", during which the arsenic pollutant in gypsum is released into the solution, and hence raises the possibility of being distributed into the product of α-HH, a potential harm that has always been neglected. Investigation of the transformation process at neutral pH revealed that the arsenate ions in solution were distributed into α-HH and generated an enrichment of arsenic by 4-6 times. Arsenate ions distributed into α-HH by substitution for lattice sulfate, adsorption on α-HH facets and occupation for surface sulfate sites. While at higher concentrations, calcium arsenate coprecipitated with α-HH or even crystallized independently. Increasing temperature accelerated the phase transformation and restrained arsenate migration into α-HH due to the lag of distribution balance. The pH of solution modulated the dominant arsenate species and decreasing pH weakened arsenate substitution capacity for sulfate in α-HH. This work uncovers arsenate distribution mechanism during the transformation of gypsum into α-HH and provides a feasible method to restrain arsenate distribution into product, which helps to understand arsenate behavior in hydrothermal solution with high concentration of sulfate minerals and provides a guidance for controlling pollutants distribution into product.