Phosphogypsum Waste Research Articles

A multicriteria analysis to assess the pollution in the southern coastal area of Sfax

The coastal marine area of Sfax (Tunisia) is a well-known zone by its high productivity and fisheries. However, it is threatened by a variety of pollution sources contributing to a degradation of the water quality. In this paper, a study involving 20 stations and 23 physico-chemical and biogeochemical parameters is proposed. Due to the multicriteria nature of the problem, De Smet et al.'s method is used to assess the pollution level in this coastal area. The application of this approach leads to three groups of stations with different pollution levels. The results show that PO3–4, BOD5, COD, MN2+, Cl– and SO2–4 are the main factors of the pollution. In addition, they indicate that the SIAPE discharges and the phosphogypsum wastes are the main source of PO3–4, Cl– and SO2–4 which explain the high COD. Thus, an urgent action leading to control the loading of these industrial wastes into the sea is a necessity in order to reduce the pollution and to avoid its propagation.

A practice to mitigate greenhouse gases from a wheat-grown soil by the phosphogypsum waste

A practice to mitigate greenhouse gases from a wheat-grown soil by the phosphogypsum waste

A multicriteria analysis to assess the pollution in the southern coastal area of Sfax

The coastal marine area of Sfax (Tunisia) is a well-known zone by its high productivity and fisheries. However, it is threatened by a variety of pollution sources contributing to a degradation of the water quality. In this paper, a study involving 20 stations and 23 physico-chemical and biogeochemical parameters is proposed. Due to the multicriteria nature of the problem, De Smet et al.'s method is used to assess the pollution level in this coastal area. The application of this approach leads to three groups of stations with different pollution levels. The results show that PO3–4, BOD5, COD, MN2+, Cl– and SO2–4 are the main factors of the pollution. In addition, they indicate that the SIAPE discharges and the phosphogypsum wastes are the main source of PO3–4, Cl– and SO2–4 which explain the high COD. Thus, an urgent action leading to control the loading of these industrial wastes into the sea is a necessity in order to reduce the pollution and to avoid its propagation.

Geotechnical Properties and Microstructure of Lime‐Fly Ash‐Phosphogypsum‐Stabilized Soil

The use of industrial waste as a potential stabilizer of marginal construction materials is cost effective. Phosphogypsum and fly ash are industrial wastes generated in very large quantities and readily available in South Africa. In order to explore the potential stabilization of vastly abundant expansive soil using larger quantity phosphogypsum waste as a potential modifier, composites with a mixture of lime‐fly ash‐phosphogypsum‐basic oxygen furnace slag were developed. However because of the presence of radionuclide, it was necessary to treat the phosphogypsum waste with mild citric acid. The effect of the acid treatment on the geotechnical properties and microstructure of expansive soil stabilized with phosphogypsum‐lime‐fly ash‐basic oxygen furnace slag (PG‐LFA‐BOF) paste was evaluated, in comparison with the untreated phosphogypsum. Expansive soil stabilized with acid‐treated PG‐LFA‐BOF paste exhibited better geotechnical properties; in particular, the high strength mobilized was associated primarily with the formation of various calcium magnesium silicide and coating by calcium silicate hydrate and calcium aluminate hydrate. The soil microstructure was improved due to the formation of hydration products. The stabilized expansive soil met the specification for road subgrades and subbase. Stabilization of expansive soils with phosphogypsum, fly ash, and basic oxygen fly ash does not only improve engineering properties of soil but also provides a solution in relation to disposal and environmental pollution challenges.

Оцінка рівня екологічної безпеки в межах зберігання гірничих відходів фосфогіпсу.

Оцінка рівня екологічної безпеки в межах зберігання гірничих відходів фосфогіпсу.

Development of the integrated model of ecologically safe utilization of phosphogypsum in environmental protection technologies

This paper focused on the development of scientific and theoretical foundations for conducting research on the environmentally safe disposal of phosphogypsum in environmental protection technologies. The biochemical direction of technological solutions for the phosphogypsum treatment as a mineral raw material to stimulate the development of the necessary ecological trophic groups of microorganisms is developed. The methodological approach was formalized in the ecological-synergetic concept of phosphogypsum wastes using. At the same time, paper focused on the interconnection in related spheres of the use of mineral carriers based on phosphogypsum with the integration of individual technological solutions in the system of protection of aquatic ecosystems, atmospheric air and the processes of restoring contaminated soils. The biochemical conversion will be able to provide efficient purification of environmental components using phosphogypsum and products of its processing as supply medium in biotechnological environmental protection systems. In the process of phosphogypsum conversion, a mineral carrier is obtained for the immobilization of microorganisms in the technologies of aquatic ecosystems protection, biochemical gas purification from sulfur compounds, in remediation processes of contaminated soils. The scheme for the determination of ecologo-microbiological parameters was developed for estimation of the effectiveness of using phosphogypsum as a mineral substrate by different groups of microorganisms in environmental protection technologies.

Rare Earth Elements Recovery and Sulphate Removal from Phosphogypsum Waste Waters with Sulphate Reducing Bacteria

Phosphogypsum waste, originating from phosphoric acid production from apatite ores, is well known for its high production rate and possible release of sulphate-rich seepage waters. In addition to negative environmental impacts, phosphogypsum waste heaps are also remarkable secondary sources of Rare Earth Elements (REE); in the phosphoric acid production process a majority of REE, occurring in apatite, are precipitated to the phosphogypsum waste. Therefore, a method treating both sulphate-rich waters and recovering REE from phosphogypsum heaps and seepage waters would offer both economic and environmental benefits. In this ongoing study, seepage waters from a phosphogypsum heap are treated with Sulphate Reducing Bacteria (SRB) and ethanol as a substrate. Sulphate is first reduced to hydrogen sulphide, which then precipitates REE as sulphides. The main challenge, low concentration of REE in seepage waters (e.g. 2.87 μg/l La, 5.13 μg/l Ce, 0.67 μg/l Y and 3.32 μg/l Nd), is overcome by utilizing continuous mode, semi-passive and cost effective column apparatus, requiring no agitation and performing both sulphate reduction and REE recovery in a single reactor. The SRB method results in a sulphate reduction rate of 40-80 % (from app. 1400 mg/l to 276-844 mg/l sulphate in the effluent) and efficient REE recovery from seepage water. The concentrate obtained from the column consists of a mixture of anaerobic sludge and precipitated REE, with respective REE concentrations of 202 mg/kg La, 477 mg/kg Ce, 49 mg/kg Y and 295 mg/kg Nd.

Investigation of the Fusion Characteristics of Ash in the Reduction of Pyrite and Phosphogypsum

The full utilization of solid waste—phosphogypsum (PG)—by reacting it with pyrite can not only produce acid but can also solve the serious issues associated with PG waste. However, this approach is limited because of crusting which blocks the rotary kiln and makes the acid production unsustainable. Hence, it is imperative to design a strategy to increase the eutectic temperature so as to prevent the generation of eutectic compounds, which always lead to crust formation, kiln-ringing, and blockage. In this study, the fusion characteristics of pyrite reduction were investigated via the determination of ash fusion points under various atmospheres as well as using different additives. The structural changes and fusion characteristics, in particular macromorphology, were observed by scanning electron microscopy. Furthermore, the optimal conditions to increase the softening temperatures were determined by means of single-factor and orthogonal experiment methods.

Study of Granulated Gypsum Hardness Coming from the Granulation Process in Rotating Disk

The granulation process is a unit operation with broad application in the fertilizer industry. The granular fertilizer has a better physical appearance, facility of agricultural application and elimination of fugitive dust in the production and bagging units. Phosphogypsum is a residue from the production of phosphate fertilizers. It known that for every 1 t of phosphate fertilizer produced, about 4 t of phosphogypsum are obtained, causing problems in storage and risks to the environment. Such problems may be minimized by granulating the waste phosphogypsum and using it in agriculture. This work aims at the construction of a laboratory-scale rotating disk granulator with a pre-established combination of reagents to promote granulation of the waste from phosphate fertilizer production. For construction of the equipment a theoretical study was performed in order to establish the principal variables influencing the granulation technique and the dimensions required for building the granulator. The equipment attained the expected results and the disc speed (22 to 250 rpm) and disc inclination (0 to 90 degrees) can be manipulated. In this paper three binders used were: Manioc starch, carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA), each at three different concentrations. The tests were conducted using a rotating disk granulator and hardness tests on a universal mechanical testing machine. The figures of merit used in this study were percentage particle size, hardness and sphericity of the granules obtained. With the analysis of the data, it can be concluded that the granulation process was adequate, considering the settings employed.

New method for carbon dioxide mineralization based on phosphogypsum and aluminium-rich industrial wastes resulting in valuable carbonated by-products

A new carbon mineralization method was designed based on a sequestration agent synthesised exclusively from industrial wastes. Phosphogypsum waste from the fertiliser industry was dissolved into caustic aqueous waste from the aluminium anodising industry. The resulting precipitate consisted of katoite (Ca3Al2(OH)12, a Si-free hydrogrossular solid solution end-member of the Al-containing hydrogarnet) and thenardite (Na2SO4); the latter easily removed by rinsing with water. The carbonation performance of this katoite-rich sequestration agent was evaluated using two different methods, by bubbling in aqueous media and by weathering. Both procedures yielded high carbonation efficiencies (80% and 100%, respectively), and resulted in a solid precipitate composed primarily of calcite (CaCO3) and aluminium hydroxide (Al(OH)3). Priority attention was given to the transfer of trace elements and radionuclides of the uranium series typically present in the phosphogypsum. Results confirmed that the traces were transferred to resulting final solid carbonate at concentrations similar to those present in the raw phosphogypsum. In conclusion, these carbonated minerals would trap substantial amounts of CO2 and produce final materials with similar civil engineering uses to those proposed for current phosphogypsum wastes. This work offers new methods for jointly managing specific industrial wastes oriented to more sustainable industrial processes and controlling CO2 emissions.

First insight into microbial community composition in a phosphogypsum waste heap soil.

The aim of this study was to investigate the soil microbial communities of a phosphogypsum waste heap. The soil microbial community structures can differ over time, as they are affected by the changing environmental conditions caused by a long-term exposure to different kinds of pollutions, like is the case of soil in the post-production waste area in Wiślinka (in the northern part of Poland) currently undergoing restoration. Our analyses indicated that the most abundant phyla were Proteobacteria, Acidobacteria, and Actinobacteria, and generally such an abundance is common for most of the studied soils. The most dominant class were Alphaproteobacteria, with their participation in 33.46% of the total reads. Among this class, the most numbered order was Sphingomonadales, whereas among this order the Sphingomonadaceae family was the most abundant one. The Sphingomonadaceae family is currently in the center of interest of many researchers, due to the ability of some of its members to utilize a wide range of naturally occurring organic compounds and many types of environmental contaminants. This kind of knowledge about microbial populations can support efforts in bioremediation and can improve monitoring changes in the contaminated environments.

Optimization of the phosphogypsum granulation for bio-desulfurization systems

The paper focused on describes a laboratory model of granulation phosphogypsum. Phosphogypsum is a kind of gypsum that occurs as a by-product and was obtained from phosphate rock during the production of phosphoric acid in fertilizer plants. The most optimal conditions for the granulation process were determined. The optimal average grain size of phosphogypsum granules of mineral download for the development of biofilms was determined. The features of the development of matrix of sulfur-oxidizing bacteria under dehydrate phosphogypsum granules was studied. The parameters of granulation process were estimated such as granulation time and humidity of phosphogypsum at process. The optimum humidity range with addition of hydrated lime was observed during the process of dihydrate phosphogypsum granulation. The regression equations for approximated of the impact of these factors for process optimization granulation was developed. The biofilm of biomass was found in the surface of the granules after Micro X-ray analysis. Bacterial matrix penetrates deep into the pores of the thin pellet. The mineral components of granulated material were subjected to enzymatic transformation by cells, forming an internal "bioactive layer". The clusters of amorphous sulfur deposits were formed on the surface of the phosphogypsum granular load, which indicates the active metabolism of Thiobacillus. Using the bio-activity properties under optimum conditions for treatment of the phosphogypsum waste leads to obtain a product that can be safely used in many biotechnological applications.

Ammonium sulfate preparation from phosphogypsum waste

The Egyptian phosphogypsum waste is treated using sulfuric acid prior the ammonium sulfate production. The relevant factors that would affect the removal efficiencies of some impurities are studied. The optimum conditions of the treatment are 8 M sulfuric acid solution and 1/4 solid/liquid ratio for 30 min contact time at 80 °C. Moreover, the optimum conditions of the ammonium sulfate preparation are 10 g of the suspended impure or purified phosphogypsum in 40 ml of 3% ammonium sulfate solution (as initiator), 1/4 solid/liquid ratio at pH7 at an addition of an excess ammonium carbonate, and 150 rpm stirring speed for 4.0 h contact time at 55 °C as well as the 5 mg of barium chloride is added to remove the radium in the ammonium sulfate product. Finally, the ammonium sulfate is crystallized and the chemical analysis of the product shows 20% nitrogen and 23.6% sulfur. Therefore, the purity of the obtained ammonium sulfate is 95% from the purified phosphogypsum.

Phosphogypsum Waste Used as Reinforcing Fillers in Polypropylene Based Composites: Structural, Mechanical and Thermal Properties

The industrial production of wet phosphoric acid in Morocco led to controversial stockpiling of waste phosphogypsum by-products resulting in the release of significant amounts of toxic impurities in salt marshes. In the framework of fighting against global climate change and efforts to reduce toxic industrial wastes (phosphate industry), this work presents a new polymer composite based on phosphogypsum (PhG) and polypropylene (PP).The compounds were produced by twin-screw extrusion and injection molding. The morphological results show that good affinity between PhG and PP led to good particle dispersion/distribution in the polymer matrix. Thermal characterizations showed that PhG particles improved the thermal stability of PP with a 50 °C increase at 40 wt%. The optimum tensile modulus was also obtained at 40 wt% with a 74 % increase over neat PP. Dynamical mechanical analysis showed that PhG addition can improve the viscoelastic properties of PP for potential applications under dynamic stress. Overall, it can be concluded that PhG is potential reinforcing filler for the production of PP composites and represents a promising avenue for the valorization of this waste as a new raw material while resolving some environmental issues.

CO2 sequestration through mineral carbonation of waste phosphogypsum using the technique of membrane electrolysis

Mineral carbonation is considered to be a promising method for sequestering atmospheric CO2. This paper studied the technical feasibility of mineral carbonation of waste phosphogypsum assessed by investigating the details of the electrochemical reaction in an electrolytic cell. In a series of experiments, phosphogypsum was shown to exhibit high carbonation reactivity at conditions of room temperature and atmospheric pressure. Results show that preparation of a catholyte solution with an optimal alkalinity of pH 11 will enable production of large quantities of calcium carbonate of purity greater than 90 % at a carbonation rate of 95 %. In comparison with the traditional electrolysis process, membrane electrolysis can significantly reduce the necessary cell voltage required for the reaction to take place, while avoiding the production of chlorine gas. Injection of CO2 in the cathode chamber of the electrochemical cell decreases the pH of the catholyte, thereby depolarizing the cathode and reducing the energy consumption of the entire electrolytic process. This renders the method to be economically feasible.

Location and stability of europium in calcium sulfate and its relevance to rare earth recovery from phosphogypsum waste

Rare earth elements (REE) are technology drivers, essential for applications ranging from clean energy technologies to biomedical imaging. Thus they are “critical elements” and it is desirable to find additional RE domestic sources and explore green extraction technologies to overcome their supply risk. Phosphogypsum, a major byproduct of the phosphate fertilizer industry, incorporates a significant amount of RE from the apatite source rock and thus is a potential alternate source of RE. To know the accessibility and extractability of RE from phosphogypsum, it is important to understand the location and nature of RE binding. Here, we report the synthesis of analogs of RE-doped phosphogypsum, with europium (Eu) as a model RE. Using several characterization tools we conclude that the majority of Eu is on the surface of the calcium sulfate crystal as a separate secondary phase, namely a metastable amorphous/nanocrystalline precipitate in which Eu is associated with phosphate and sulfate as counterbalancing ions. The rapid precipitation at low temperature could be responsible for this behavior, which may not represent equilibrium, and our experiments are comparable in the timescale with the fast phosphogypsum precipitation in the industrial process. These results suggest that the Eu is not entrapped by ionic substitutions in the calcium sulfate lattice. Thus RE should be extracted relatively easily from phosphogypsum using methods that extract the RE from its surface.

Capture and storage of CO2 into waste phosphogypsum: the modified Merseburg process

We evaluated the chemical sequestration of carbon dioxide into the phosphogypsum from the Lowveld region of South Africa. The phosphogypsum was converted to saleable ammonium sulphate and precipitated calcium carbonate in a modified Merseburg process. The heat from the ammonium carbonate formation exothermicity increased the temperature in the gypsum conversion reactor contents by 35 K, significantly reducing the heating requirements to achieve the reaction temperature of 343 K. The modified process will lower capital layout but no fundamental energy superiority or inferiority to the original Merseburg process. The gypsum conversion efficiency of 95 % was achieved. The purity of the ammonium sulphate produced is comparable to the chemical grade, commercially available in South Africa. The calcium carbonate precipitated as calcitic scalenohedral polymorphs with a mean size of 3.4 μm in diameter. The economic feasibility study must be done to determine the cost implication of the omission of the carbon dioxide scrubbing towers in the modified Merseburg process.

STABILIZATION OF SOIL SWELLING FOR CONSTRUCTION PURPOSES, USING PHOSPHOGYPSUMAND SODIUM CHLORID

This paper deals with the improvement of soil swelling for purposes of constructions by adding industrial waste Phosphogypsum (PG), in addition to the chemical additive sodium chloride (NaCl) to reduce its expansiveness and improve its characteristics for many earth work construction, the test results showed significant decrease in the swelling properties and pronounced reduction in the liquid limit, plastic limit and plasticity index of the clay by increasing the ratios of PG and NaCl. Also the results from x-ray diffraction (XRD) analyses of bentonit only and the mixture (1.2% PG+3% NaCl+95.8% Bent.) showed that, large amounts of Montmoronite clay mineral were approximately transformed to other phases during the reaction. Reaction products are non-swelling clay mineral commonly Kaolinite this is because, the mineralogy of both clay minerals reflects that, Montmoronite is an immature clay mineral while Kaolinite is a mature clay mineral. This maturity state may be attained through the chemical reaction with these additives. So, the PG industrial waste helps to improve the physical characteristics of soil swelling and the results present a very important factor for constructions purposes.

Rare earths concentration from phosphogypsum waste by two-step leaching method

In the present work, Tunisian phosphogypsum was considered as a source of rare earths. After examining the particle size distribution of the raw sample and its rare earths repartition by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), a double sulfuric leaching of the sample led to rare earths dissolution, then, the evaporation of the acid liquor allowed to recover a rare earths-rich solid. During the process, all the obtained solids were identified by infrared spectroscopy and X-ray powder diffraction, and rare earths content was also measured after each step by ICP-MS. Analytical results showed that the first acid leaching allowed essentially to impurities dissolution (such as fluorides and phosphates) and so rare earths enrichment in the residue (about 52%), whereas the second leaching led to the dissolution of such elements in the sulfuric acid liquor (about 50%). The crystallized solid obtained after the evaporation stage corresponds to a mixture of anhydrite-monetit phases with a total rare earths enrichment of about 86%. The method showed also its efficiency for purifying the phosphogypsum which can be used safely in industrial applications. Photoluminescence measurements carried on the phosphogypsum sample and the crystallized solid allowed the observation of some rare earths emissions (cerium, europium and samarium) and confirmed as well their enrichment in the final solid at the end of the process.

Preparation of Nd2O3 through the extraction separation of rare-earth concentrate recovered from phosphogypsum

We present a study of the extraction separation of a rare-earth group concentrate (GC) recovered from phosphogypsum waste from OAO Voskresensk Mineral Fertilizers using different extractants, followed by the preparation of neodymium oxide suitable for the fabrication of magnets. The proposed process has been tested using a pilot GC separation apparatus which includes three sequential automatic cascades of EC-10FA centrifugal extractors (Skaigrad Group).