Phosphate Industry Research Articles

Characterization of Phosphogypsum Blended Red Mud as Geo-material

Red mud (RM) is a toxic material discarded after extraction of aluminum from the Bauxite and is disposed of in the form of slurry or as low-water content cake as stacking. Either form of disposal is a threat to the environment due to the alkaline nature of RM and also consumes vast tracts of land. Occasional failure of the dyke of the RM pond causes a slurry flooding over a large area, which creates geo-environmental problems. The highly alkaline nature of the RM restricts its bulk utilization, as the high pH value supports the leaching of the heavy metals. On the other hand, phosphogypsum (GYP) is an acidic (pH < 7) material produced from the phosphate industry, blending of which can reduce the alkalinity of the mixture. In the present study, an attempt has been made to use GYP blended RM as a resource geomaterial. The GYP is mixed with RM in 5%, 10%, and 15% on a dry basis to evaluate the chemical, physical, and mechanical properties of the newly developed resource material after 3, 7, and 28 days of curing period. The addition of 5% and 10% GYP lowered the maximum dry unit weight, however, 15% GYP increased the maximum dry unit weight upto 15.47 kN/m3. The 28-days strength of 5%, 10%, and 15% GYP blended RM was found as 433.57 kPa, 592.44 kPa, and 711.53 kPa, respectively, which further increased to 752.11 kPa, 1120.38 kPa, and 1371.80 kPa, respectively, after alkali activation.

Assessment of the mobility of potentially toxic trace elements (PTEs) and radionuclides released in soils stabilized with mixtures of bentonite-lime-phosphogypsum.

Phosphogypsum (PG) is a solid by-product of the phosphate industry, rich in contaminants and produced in large quantities. Raw materials and stabilized specimens, consisting of bentonite-lime-PG mixtures, were characterized by mineralogical, microstructural, chemical, alpha-particle, and gamma-ray spectrometry analysis before hydration and after hardening. Compressive strength and leaching tests were performed on hardened specimens. The physicochemical parameters and chemical composition of leachates from raw materials and hardened specimens were determined. PG contains high concentrations of natural radionuclides, specially from U series. Uranium-238 activities are double in PG than the worldwide average for soil values. The mobility of PTEs from PG is Cd (2.43%), Zn (2.36%), Ni (2.07%), Cu (1.04%), Pb (0.25%), and As (0.21%). Cadmium is the cation most easily released by PG in water with a concentration 0.0316mgkg-1. When PG is added to bentonite-lime mixture, cadmium is no longer released. The radionuclide 238,234U and 210Po predominates in the leachates of PG. However, the activity of 210Po becomes negligible in the leachates of bentonite-lime-PG mixtures. The addition of PG to bentonite-lime mixtures facilitates the trapping of trace elements (PTEs) and radionuclides, providing potential applications for PG as road embankments and fill coatings.

Study on Wastewater Treatment in the Textile Industry by Adsorption of Reactive Red 141 Dye Using a Phosphogypsum/Vanadium Composite Developed from Phosphate Industry Waste

Study on Wastewater Treatment in the Textile Industry by Adsorption of Reactive Red 141 Dye Using a Phosphogypsum/Vanadium Composite Developed from Phosphate Industry Waste

Assessment and Mitigation of Groundwater Contamination from Phosphate Mining in Tunisia: Geochemical and Radiological Analysis

Groundwater contamination in the Mediterranean Basin is a severe problem that has a significant impact on environmental ecosystems and human health. The unconventional uranium and the potentially toxic elements (PTEs) of phosphate rocks are the principal contaminants in the phosphate mining industry in Tunisia. Phosphogypsum (PG) results from the valorization of phosphate to fertilizers and phosphoric acid. PG stocks can be used in cement production, brick manufacturing, and soil amendments in desertic land, and can be resolved by using nanomaterial adsorbents. In the flat area of the study area, the increase in radioactivity (40K) is due to abusive fertilizer use. Geochemical and radiological analyses in the northern part of Tunisia and its karst shallow aquifer indicate significant contamination levels. The northern part exhibits moderate contamination, whereas the karst shallow aquifer shows higher contamination levels, particularly with elevated nitrate concentrations. In the phosphate basin, both washing phosphate and phosphogypsum reveal high levels of radioactive elements, with the latter showing especially high concentrations of radium. The shallow aquifer in this region has moderate contamination levels, while the deep geothermal aquifer also shows noticeable contamination but to a lesser degree compared to the shallow aquifer. The shallow groundwater is characterized by a higher value of radioactivity than the groundwater due to the contamination impact from the phosphate industry and the cumulative radioactivity disintegration. Finally, the nanoparticles and the electrostatic adsorption can decrease the PTEs and radionuclides from the contaminated water in the study area. Moreover, other key issues for advancing research on groundwater contamination are proposed in this study. It is time to valorize this PG and the other mines of (Fe, Pb, and Zn) in the socioeconomic sector in Tunisia and to minimize the environmental impact of the industrial sector’s extraction on groundwater and human health in the study area.

Radiological environmental impact assessment for phosphate industry in Korea

NORM is used as a raw material in various industries worldwide. According to the IAEA, radiological effects may occur in the environment due to raw materials and by-products generated from NORM industries. The objective of this study was to assess radiological environmental impact of the phosphate processing industry to identify the radiological effects on the general public. The resident farmer scenario was chosen as the exposure scenario due to the living characteristics of the public around the facility and the conservatism of the assessment. The RESRAD-OFFSITE code was used to evaluate the radiation dose to the public. The maximum radiation dose to the public was 6.13 × 10−3 mSv/y. Main exposure pathways were aquatic food ingestion, radon inhalation, and meat ingestion. The uranium series accounted for about 99 % of the total radiation dose, while the thorium series and K-40 nuclides accounted for less than 1 %. These study results can be used for management of radiological impact to the public around domestic NORM industries.

Sustainable strategy for rehabilitating phosphate mining sites and valorisation of phosphate industry by-products and sludge using pistachio tree (Pistacia atlantica), false pepper (Schinus molle), and eucalyptus (Eucalyptus globulus) trees

The development of anthroposols has been proposed as a new environmentally friendly approach to ensuring the successful revegetation of phosphate mining sites. The phosphate industry's by-products, including phosphogypsum (PG), phosphate sludge (PS), and sewage sludge (SS), can be valuable resources in restoring the ecological balance of mined soil areas. The aim of this study was to safely and sustainably restore the ecological integrity of the phosphate mining site through the evaluation of nutrients and heavy metals dynamics in soil and plant tissues of three tree species and treated by-products containing 65 % PG, 30 % PS, and 5 % SS. The tree species used were Pistacia atlantica, Schinus molle, and Eucalyptus globulus. The experimental layout was a randomised complete block design with six replicates and three treatments. Growth diameter, height, nutrient uptakes and heavy metal dynamic were evaluated from the rhizosphere soils and plant tissues over two years. Hierarchical head maps of correlations between the measured growth parameters, soil and nutrient uptakes of the tree species were analysed using a phylogenetic generalised linear mixed model. S. molle and E. globulus had higher average diameter and height than P. atlantica plants. P. atlantica and S. molle showed greater nitrogen, phosphorus, potassium, calcium, and magnesium concentrations than E. globulus trees. Tree growth parameters were closely linked to soil nutrient bioavailability. The heavy metal accumulation ratio was higher in the E. globulus and S. molle leaves than in stems. Using by-products could be valorised for rehabilitating mine sites together with E. globulus and S. molle species.

New sustainable strategy for rehabilitating phosphate mining sites using phosphate industry by-products and sludge integrating Argan, Carob, and Olive trees

In semi-arid context, the development of anthroposol from phosphate industry by-products and sewage sludge could be a new approach for sustainable phosphate mining soils. The objective of this 2 years field study carried out at Benguerir phosphate mine, was to evaluate nutrients and heavy metals dynamics in the soil-plant system of three species planted on anthroposol consisting of a mixture of 65% phosphogypsum (PG), 30% phosphate sludge (PS), and 5% sewage sludge (SS). The experimental layout was a randomized complete block design with six replicates and three species: argan, olive, and carob. No fertilizer was applied to the different plots. Heights and diameters of the different species were measured. Species were pruned, and leaves and stems were separated. The nutrients (N, P, K, Ca, and Mg) and heavy metals (Cd, Cu, Cr, Pb, Ni and Zn) contents in both soil and plant part were determined. The results of the Pearson correlation showed significant correlations between height and diameter of the different species. The strongest correlation was observed for the argan tree. Furthermore, nutrient contents in the rhizosphere of species were significantly reduced, excepted Ca. Also, nutrient contents in leaves were significantly higher than those in the stems. In addition, the concentration of heavy metals in argan, olive and carob leaves, were below international standards. In semi-arid contexts, argan tree could be the best candidate for revegetating mining sites and this anthroposol (65% PG – 30% PS – 5% SS) could be a new approach to rehabilitate mining site on large scale.

Discussion on “Design of acid-geopolymers based on clays by-products for methylene blue removal from wastewater” [Applied Clay Science 245 (2023) 107126]

The subject paper deals with the sorption of dyes (mainly methylene blue) on originally prepared geopolymers based on clay-rich wastes from the phosphate industry. However, the results of sorption experiments are marred by errors of interpretation that limit their validity. In particular, it is well known that linearization of the equations used to model sorption kinetics (pseudo-first and pseudo-second order) and isotherms (Langmuir and Freundlich) should be avoided, as this may bias the calculated values. In addition, other selected models use incorrect equations, as in the case of the intra-particular diffusion kinetic model and the Temkin isotherm. Some additional results are inaccurate or illogical, such as the study of the influence of pH. We hope that our comments and suggestions will serve to correct the discussed paper and avoid repetition of these errors in future scientific literature.

Design and Implementation of Sampling Wells in Phosphate Mine Waste Rock Piles: Towards an Enhanced Composition Understanding and Sustainable Reclamation

Establishing a circular economy in mining begins with a dedicated sampling strategy as its fundamental phase. This specific approach is crucial for enhancing resource retrieval and isolating essential minerals from mining residues. By carefully examining and defining the makeup of waste materials, mining activities can discover overlooked possibilities, promoting sustainability. A thoughtfully planned sampling strategy not only reduces environmental harm but also sets the stage for the effective use of resources. In doing so, the mining industry can shift towards a circular model, adhering to the principles of waste reduction, material reuse, and ultimately promoting a more environmentally conscious and economically viable industry. In the phosphate industry and during the pre-concentration process of phosphate ore through screening, significant amounts of mining waste, consisting of various lithologies including indurated and fine phosphate, coarse-grained silicified phosphate, limestone, and marls, are deposited in waste rock stockpiles. Collecting representative samples from these heterogeneous materials presents challenges in accurately characterizing the entire stockpile. To overcome this issue, circular mining wells were implemented as a novel sampling method in waste rock stockpiles, enabling the collection of intact representative samples. This paper shares a successful experience in constructing three concrete-lined wells within a phosphate mine waste rock stockpile measuring 662 m in length, 240 m in width, and ranging in height from 0 to 65 m. The wells were dug at various depths, ranging from 20 m to 55 m, with a circular section and a diameter of 1.5 m. An integrated method utilizing analytical techniques in conjunction with numerical modeling via Robot Structural Analysis software (version of 2020) was utilized to assess the stress on the well supports and confirm their stability. This methodology serves as a valuable tool for evaluating the stability of similar wells, ensuring the safety of operators. The structural model yielded a stress level of 1 MPa, which aligned with the values obtained from the analytical model. Sensitivity analysis was performed on various parameters (friction angle, Poisson Ratio, and gravity), and the safety factor consistently remained above 1.5 for all scenarios investigated up to a depth of 60 m. Consequently, this study demonstrates that concrete-lined wells can be utilized safely for intact sampling in waste rock stockpiles. This sampling operation will allow the pursuit of optimizing resource utilization and enhancing environmental sustainability, by studying phosphate distribution in the Phosphate Mine Waste Rock (PMWR) for better recovery.

Anaerobic bioremediation of acid phosphogypsum stacks leachates: Assessment of leachate’s biochemical changes and microbial community dynamics

Phosphogypsum (PG) is the largest by-product of the phosphate industry. Nearly 300 M tons of PG are annually discarded, of which 58% is dry stacked. The exposure of PG stacks to rainwater and processed waters moisture creates hydraulic pressure, generating acidic PG leachates into nearby aquifer systems. Because of its elevated levels of sulfates, phosphorus (P) and metals, the PG water leachate can negatively affect the surrounding environments. This work investigates the effect of water activity on the PG leaching, by studying the effect of different PG:Water ratios on the leaching process, followed by the anaerobic bioremediation of PG leachate through biological sulfate removal activity (BSRA). This later involves using sulfate-reducing bacteria consortium within an anaerobic bioreactor, allowing a simultaneous monitoring of the leachate’s biochemical changes, impurities removal, and microbial community dynamics. The results determined the highest sulfates and impurities leaching from PG with a PG:Water ratio of 1:200 (w:v). Subsequently, the biological treatment of the leachate exhibited an efficient removal of sulfates (79%), P (99%) and chemical oxygen demand (93%), with a substantial decline in metal concentrations (Cd, As and Al by 99%, and Zn by 70%) from the leachate. Moreover, the acidity of the leachate was also neutralized through the BSRA process by increasing the pH from 4 to 7.52. Furthermore, the microbial community dynamics unveiled a significant correlation between the leachate’s biochemical changes and co-existence of specific sulfate-reducing bacteria within various bacterial phyla, including Desulfobacterota, Firmicutes, and Proteobacteria, allowing efficient and eco-friendly bioremediation process of PG leachate.

Direct synthesis of multiple heteroatoms functionalized mesoporous silica adsorbents from phosphate industry mining byproducts. Decontaminating water from Pb(ii) ions as an application case

Sustainable synthesis of heteroatom-enriched mesoporous silica from phosphate mining waste for selective Pb(ii) adsorption, bridging waste valorization with environmental remediation.

Why and when do reserves estimates in mining change and innovations take place?

This commentary is a practice expert essay based on review of scientific papers on phosphorus scarcity that provides a resumé of arguments relating to adequacy of phosphate rock (PR) resources to supply future requirements and an explanation as to why, although we cannot know how much will be available in future, we can say that the static lifetime is much more likely to be of the order of hundreds or even thousands of years rather than decades. Once the knowable facts are established, a case can be made for moving towards increased phosphate recycling and loss-reduction, based on the current inefficient use and the consequential harm done to the environment. Whilst these concerns are understandable, given that phosphate resources are finite and unsubstitutable, it is important to derive a true perspective in order that the most efficient use of financial and human resources can be deployed by governments. An assertion in 2010 that phosphorus mining would begin to be resource-constrained within decades proved false, but continues to be referred to by those advocating resource governance. Such assertions, when proved not to be accurate, run the risk of validating a ‘cornucopian’ view of mineral resource adequacy and diminish the tenets of ecological economics which, among other things, prescribe a move towards a circular economy, by cutting losses in the supply chain and increasing recycling. The phosphate supply industry has generally been less concerned about potential resource constrains than the academic community. It is true that, apart from a few larger state-owned producers, this lack of concern partly results from the industry's shorter-term economically-driven perspective which tends towards the cornucopian view. This short-term perspective of the commercial industry is at odds with the long-term mitigation of the impacts of mining that is a feature of ecological economics. In the phosphate industry mining and chemical processing has certainly led to major negative environmental legacies and impacts being deferred to future generations.

Acidification and alkali precipitation for phosphorus recovery from municipal digested sludge

AbstractMunicipal digested sludge (MDS) has considerable phosphorus content that is between 1% and 15% in dry matter and it is a potential source for phosphorus recovery. A high amount of MDS is generated from sewage treatment plants in large cities and has many environmental concerns with its organic and inorganic constituents. In this study, phosphorus was recovered by precipitation with Ca(OH)2 and NaOH. Acid pretreatment was applied to MDS with H2SO4 and 58.7% of phosphorus was extracted from the solid phase to the liquid phase at pH 2. Up to 99% of dissolved phosphorus in the liquid phase was recovered with Ca(OH)2 and NaOH. Almost similar phosphorus precipitation rates were achieved with both bases but higher phosphorus contents (17% as P2O5) in precipitates were obtained by NaOH. The product obtained in this study can serve as a high‐quality raw material substitute for the low‐grade phosphate rocks (<15% P2O5) commonly utilized in the phosphate industry. Furthermore, this research presents a practical, environmentally friendly and cost‐effective approach for sustainable sludge management and phosphorus production.

Typology of planktonic food webs and associated emerging properties as indicators of the ecological status of a permanently disturbed Gulf of Gabès

This study highlights the importance of coupling the typology of planktonic food webs and their emerging properties to better describe the ecological status of an ecosystem under permanent disturbance mainly caused by phosphate industry. Linear inverse models were built to describe four stations under various levels of nutrient pressure, using the Markov Chain Monte Carlo method to estimate known and unknown carbon flows, later used to calculate food web typology ratios. Ecological network analysis (ENA) was used to describe the structural and functional properties of each food web. Based on the food web typology ratios, three planktonic trophic pathways (PTP) with different functional indices were distinguished according to nutrient stress. The microbial food web dominated in the least nutrient-rich environment. It mainly relied on phytoplankton production (picophytoplankton <2 μm) that was mainly transferred by the high microbivory of protozooplankton. In contrast, the herbivorous food web developed in the most nutrient-rich environment, where biogenic carbon was mainly produced by large phytoplankton (microphytoplankton >10 μm) and channeled to higher trophic levels by herbivorous protozooplankton and metazooplankton. In the other two stations – moderately nutrient-rich systems – the PTP acted as a multivorous food web. Phytoplankton (small and large size fractions) and non-living components (detritus and dissolved organic carbon) played a significant role in carbon production, and competed with protozooplankton and metazooplankton for its transport. ENA indices revealed that the herbivorous food web, with the highest total system throughput and lowest relative Ascendency and cycling, was the most active but the least organized and stable system. In contrast, the microbial food web, with the lowest total system flux and highest Ascendency, was least active but more organized than the herbivorous food web. The multivorous food web displayed the most recycling and most organized system, with high values of the detritivory-to-herbivory ratio, cycling and Ascendency. In addition to ENA indices, which are considered effective tools for studying the structural and functional properties of food webs, marine ecosystem management efforts heavily focus on using the “marine food web” as a descriptor of the system's ecological status. However, we suggest that the combination of food web typology and ecological indices could be used as an effective tool for the management and assessment of ecosystem health wherever possible, as well as for the study of anthropogenic pressures.

Lecithin as an ecofriendly amphoteric collector foaming agent for the reverse flotation of phosphate ore

The development of more widely available, effective, economical, and environmentally friendly reagents is one of the major prospects of the phosphate industry. In this work, an eco-friendly reagent based on lecithin was successfully elaborated and adopted as a new amphoteric collector and frother, both for the flotation of phosphate ore. The proposed reagent was evaluated regarding its physicochemical properties (critical micelle concentration CMC, acidity index, composition) by conductivity, and ultra-high performance liquid chromatography (UHPLC). The performance of the collector in phosphate ore flotation was investigated by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectrophotometry. Furthermore, the results of FTIR, SEM, and XRD analyses show that the lecithin collector has a good ability to collet calcite, dolomite and quartz. It has also been observed that francolite and quartz can be successfully separated at a pH of 5 and a lecithin concentration of 40 mg/L. Similarly, an effective separation of francolite and carbonate gangue (dolomite and calcite) can be achieved at pH 8.5 and 40 mg/L lecithin concentration. In addition, flotation tests and X-ray fluorescence show that the required quality of phosphate concentrate was obtained at 31.05% P2O5 with a recovery of 98.21% at pH 5. Similarly, 32.39% P2O5 grade was obtained with 96% recovery at pH 8.5. Thus, the results obtained suggest that lecithin has significant potential as an efficient and environmentally friendly collector for the development of selective flotation in phosphate concentration circuits.

ECOLOGICAL RISK ASSESSMENT OF HEAVY METALS ACCUMULATION IN SOIL AND ZYGOPHYLLUM ALBUM ALBUM: A CASE STUDY OF INDUSTRIAL PHOSPHATE VICINITY, TUNISIA

Contents and spatial distribution of heavy metals (Zn, Cu, Cd, Ni, As, Pb, Al and Ba) in the fine fraction of surface sediments and in Zygophyllum album shrub of zones influenced by phosphate industry in the region of Gabès, as well as in a control site (Sidi Ejjehmi) were determined. For the assessment of the level of sediment pollution, several parameters were calculated, including enrichment factor (EF), contamination factor (CF), Pollutant Load Index (PLI), Risk factor (Er), potential ecological Risk Index (Ri), Geoaccumulation Index (Igeo), Electrical Conductivity (Ec), Organic Matter (OM) and pH.Whereas, Bio-Concentration Factors (BCF) and Translocation Factors (TF) are calculated for the evaluation of pollution degree in Zygophyllum album. The soils of Gabès are characterized by a high average relative concentration of As, Ba, Cd, Cu, Ni, Pb, Al and Zn in all the study sites, indicating contributions from anthropogenic sources. The Igeo and the PLI of heavy metals show that all study sites are heavily polluted. All the EF values of all trace metals from Gabes sites (above 10), indicate a very significant enrichment in soils. The PCA, AC and correlation matrix suggest that soils are mainly polluted by As, Ba, Cd, Cu, Ni, Pb, Al and Zn. For all studied metals, the values of TF in Z. album from Gabes sites are greater than 1 except for Al at S2. All metals studied, except Cd, are more accumulated in shoots than in roots. Values of BAF are greater than 1, as well as TF values are greater than 1, so Z. album of Gabes can be considered as phytoremediator in the case of those studied metals. For Cd, TF is greater than 1 and BCF is less than 1, Z. album can be considered as a phytostabiliser for this metal.

Waste to wealth: Synthesis of hydrocalumite from Moroccan phosphogypsum and aluminum wastes

Each year, the phosphate industries in Morocco discard over 20 million tons of phosphogypsum into the Atlantic Ocean, posing a significant threat to aquatic life and causing potential long-term damage to ecosystems due to the accumulation of harmful substances. Hence, developing eco-friendly and cost-effective strategies to valorize phosphogypsum is vital to protect ecosystems and human health. This study aims to provide a concrete and efficient strategy for exploiting phosphogypsum and aluminum wastes in the preparation of hydrocalumite using the co-precipitation method. The synthesis strategy's effectiveness was assessed through a comprehensive analysis of the phosphogypsum-based hydrocalumite using various techniques, including FT-IR spectroscopy, X-ray powder diffraction, scanning electron microscopy (SEM), Energy-Dispersive X-Ray (EDX) analysis, X-ray fluorescence (XRF), and inductively coupled plasma optical emission spectrometry (ICP-OES). In addition, the structure was refined to discuss the arrangement of the polyhedrons occupied by the different ions in the hydrocalumite framework. It was found that the phosphogypsum-based hydrocalumite exhibited chemical and structural properties comparable to those of conventionally synthesized hydrocalumite, suggesting its potential applicability in diverse fields, including catalysis, cement and concrete production, polymer additives, medicine, and environmental remediation. Overall, in this work, the Moroccan phosphogypsum and aluminum wastes proved to be effective precursors of hydrocalumite, with structural and chemical properties presumably close to the conventional hydrocalumite.

Effect of alkaline leaching of phosphogypsum on sulfate reduction activity and bacterial community composition using different sources of anaerobic microbial inoculum

Phosphogypsum (PG), a by-product of the phosphate industry, is high in sulfate, (SO42−), which makes it an excellent substrate for sulfate-reducing bacteria (SRB) to produce hydrogen sulfide. This work aimed to optimize SO42− leaching from PG to achieve a high biological reduction of SO42− and generate high sulfide concentrations for subsequent use in the biological recovery of elemental sulfur. Five SRB consortia were isolated and enriched from: IS (Industrial sludges), MS (Marine sediments), WC (Winogradsky column), SNV (petroleum industry sediments) and PG (stored Phosphogypsum). The five consortia showed reduction activity when using PG leachate (with water) as source of SO42− and lactate, acetate, or glucose as the electron donor. The highest reduction rate (81.5 %) was registered using lactate and the IS consortium (81.5 %) followed by MS (79 %) and PG (71 %). To enhance the concentration of leached SO42− from PG for future utilization with the isolated consortia, PG was treated with NaOH solutions (2 % and 5 %). SO42− release of 97 % was achieved with a 5 % concentration and the resulting leachate was further diluted to target a SO42− concentration of 12.4 g·L−1 for utilization with the isolated consortia. Compared to water leachate, a significantly higher reduction rate was registered (2 g·L−1 of SO42) using the IS consortium, demonstrating limited inhibition effect of sulfide− concentration on SRB functionalities. Moreover, metagenomic analysis of the consortia revealed that using PG as a source of SO42− increased the abundance of Deltaproteobacteria, including known SRB like Desulfovibrio, Desulfomicrobium, and Desulfosporosinus, as well as novel SRB genera (Cupidesulfovibrio, Desulfocurvus, Desulfococcus) that showed, for the first time, significant potential as novel sulfate-reducers using PG as a SO42− source.

Process of preparing chloride-free KNS compound fertilizers from phosphogypsum waste using a quaternary phase diagram

Phosphogypsum (PG), commonly known as calcium sulfate, is a waste by-product generated during the production of phosphoric acid by the wet phosphoric acid process (WPA). It is well known that every year the phosphate industries produce a large quantity of PG around the world (i.e., Currently, global production of this waste is estimated at 300 Mt/ year), but the valorization processes of this waste are limited and low valuable. In this study, we investigated the recycling of PG by-product, which can be considered very promising sources of sulfate ions (SO42-) for the manufacturing of chloride-free KNS compound fertilizer based on potassium-ammonium sulfate ([K1−x(NH4)x]2SO4). The primary objective of this study was to develop a methodology for [K1−x(NH4)x]2SO4 synthesis and its separation process using the quaternary phase diagram K+, NH4+ / Cl-, SO42- - H2O at 25 °C. The experiment results show that it is possible to recover relatively pure (NH4)2SO4 from PG to re‐synthesize in presence of KCl the [K1−x(NH4)x]2SO4 phase, whose high quality and purity were confirmed by the combined use of several analytical and characterization techniques such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and gamma spectrometry analysis. The thermal decomposition was supplemented by Thermo-Gravimetric Analysis (TGA) coupled with Differential Thermal Analysis (DTA). The main findings of this study may assist in developing methods for valorizing PG waste by converting it into valuable fertilizer products, which are particularly suitable for cultivating chloride-sensitive crops. Thus, total or partial substitution of non-renewable resources by PG not only helps to solve the environmental pollution caused by this waste, but also reduces production costs and improves farm economics.

Treaties for "offshoring" hospital treatment of Asian patients from Christmas Island, 1963-1985: a racist chapter in the history of Australian medical care.

Treaties for "offshoring" hospital treatment of Asian patients from Christmas Island, 1963-1985: a racist chapter in the history of Australian medical care.