Phosphogypsum Samples Research Articles

Chemical performance of phosphogypsum and municipal solid waste incineration bottom ash blends for potential use as road base.

Exploring the biodegradation activity of Priestia aryabhattai 1-3I, a promising chlorpyrifos-degrading strain isolated from a local phosphogypsum landfill.

Heavy metal (HM) and naturally occurring radioactive materials (NORM) pollution is continuously increasing due to anthropogenic activities, and it is one of the global problems that pose a threat to human and environmental health. Phosphogypsum (PG), a by-product of phosphate fertilizer (PF) production, is an industrial solid waste produced in large quantities worldwide, and much of it is stockpiled. PG contains enhanced levels of toxic substances such as HMs and NORMs. The first detailed study on the determination of major-minor oxides, HMs, and NORMs contents of PGs collected from waste stockpiles at phosphate fertilizer factories (PFFs) in Türkiye was carried out using energy-dispersive X-ray fluorescence spectrometry to obtain data for the reuse of these wastes and a better characterization of the waste deposit. The major-minor oxides analyzed in the PG samples were ranked as SO3 (53.22%) > CaO (36.84%) > SiO2 (2.08%) > P2O5 (1.21%) > Al2O3 (0.13%) > Fe2O3 (0.11%) according to their average contents. The average contents (mg/kg) of HMs and NORMs analyzed in the PG samples were listed as follows: Fe (744.2) > Ti (102.1) > Zn (59.2) > Mn (28.9) > Ni (18.4) > Cr (15.2) > Co (14.6) > Cu (13.5) > Zr (10.8) > Pb (8.8) > Cd (8.5) > V (7.4) > U (4.9) > Th (4.2). The results revealed that HMs, except Cd and U, were lower than the Earth’s crust averages and maximum soil contaminant levels recommended in the Turkish Regulation on Control of Soil Pollution.

Phosphogypsum (PG)-based cemented paste backfill (PCPB) is a widely used method for the large-scale disposal of phosphoric acid waste. However, fluoride contaminants in PG pose a significant risk of groundwater pollution. Effective pretreatment methods have been developed to mitigate this issue, but there is limited research on the specific pretreatment standards needed to control fluoride leaching. This study investigates the impact of initial fluoride content (IFC) in PG samples on the strength and leaching behavior of PCPB to establish appropriate pretreatment standards. Pure CaSO4·2H2O and NaF were used to simulate PG samples with varying IFC levels. The findings indicate that lower IFC leads to stronger PCPBs after 28 days of curing. To ensure compliance with Chinese national standards, the initial fluoride concentration must be below 0.0093 wt% to prevent excessive leaching. Microlevel analyses reveal that fluoride influences the hydration reactions of C2S and C3S in cement, affecting the formation of C-S-H and Ca(OH)2. Fluoride is primarily immobilized in PCPB as CaF2, which can either form gypsum crystals within the complex structure or be adsorbed onto hydration products. This research provides crucial insights into the pretreatment standards required for controlling fluoride leaching, offering a foundation for the industrial application of PG.

Tunisia is currently faced with the extremely delicate problem of managing the millions of tons of phosphogypsum (PG) discharges which is already causing considerable environmental damage. The research carried out in this work is part of a geochemical assessment of the level of heavy metal contamination in phosphogypsum waste from the Mdhilla region (Gafsa, southern Tunisia). The assessment of ETM contamination/pollution is based on the relatively simple principles of measuring concentrations, calculating indices, and comparing them with established standards, which vary according to the nature of the element, its toxicity, and the receiving environment. Six PG samples are taken from the storage heaps right next to the chemical group's plant. Our investigations to assess the level of heavy metals contamination focused on: zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni), and cadmium (Cd). These metallic elements are measured by atomic absorption spectrometry. To achieve our objectives, we calculated several indices, such as the geo-accumulation index (Igeo), the contamination factor (FC), the degree of contamination (DC), and the sediment pollution index (IPS). The index approach enables us to predict the extent of heavy metal pollution in these PG discharges from the Mdhilla region. The Mdhilla region's PG heavy metals contents show the following order of abundance: Zn > Ni > Cr > Cd > Cu. Calculation of contamination/pollution indices reveals in principle polymetallic contamination dominated by three elements: cadmium, nickel, and copper.

Relevance. The need to develop a technology for the disposal of solid and liquid industrial waste to obtain organic-inorganic fertilizer. The growth of industrial production is accompanied by an increase in waste. In modern society, considerable attention is paid to the problem of processing man-made waste to obtain demanded products. Phosphogypsum is the main by-product of the production of fertilizers and phosphoric acid, it is a multi-tonnage waste, its storage leads to the withdrawal of vast territories from circulation. Liquid waste from pig farms also needs to be processed into organic fertilizers. Aim. To study the process of heat treatment of phosphogypsum in the presence of a reducing agent to obtain an alkalizing reagent. This will make it possible to further organize processing liquid and solid agricultural and industrial waste and produce domestic organic fertilizers Methods. Heat treatment of phosphogypsum in the presence of a reducing agent, followed by the preparation of an aqueous suspension to obtain an agent that reduces the acidity of livestock effluents. The samples of heat-treated phosphogypsum obtained during the study were characterized by X-ray phase analysis, electron microscopy. Suspensions with different pH values were obtained on their basis. Results and conclusions. The authors have studied heat treatment of large-tonnage inorganic waste of the chemical industry – phosphogypsum. It was found that the suspension of phosphogypsum heat-treated in the presence of a reducing agent has increased values of the hydrogen index, which can be used to obtain an alkalizing reagent for treating agricultural waste. The authors revealed the optimal technological modes of obtaining a reagent having the maximum pH value of the suspension: the amount of the introduced reducing agent is 0.16 mol/mol CaSO4, the heat treatment temperature is 1000 °C.

In the present experiment, two types of water-reducing agents, naphthalene (FDN) and polycarboxylic acid (PCE), were selected, and their effects on the mechanical properties of foamed phosphogypsum were evaluated. It was shown that when the water-reducing agent contents were increased, the strength of the foamed phosphogypsum first increased and then gradually decreased, and that the dry density of the foamed phosphogypsum first decreased and then gradually increased. The FDN samples had better mechanical properties and a lower dry density than the PCE samples. The effect of the water-reducing agent dose on the apparent viscosity and shear stress of the phosphogypsum slurries was in the order of 0% > 0.4% > 0.3% > 0.5% > 0.2% > 0.1%. The apparent viscosity and shear stress of the gypsum slurry mixed with 0.4% FDN or PCE were the highest. FDN and PCE both enlarged the pore size distribution range, increased the size and proportion of large pores, and decreased the total pore content of foamed phosphogypsum; however, the effect of PCE was more significant. The foamed phosphogypsum slurry mixed with 0.4% FDN had the highest total pore content. Among the samples, the total pore content of foamed phosphogypsum A was able to reach 91% and the total pore content of foamed phosphogypsum B reached 77%; the lowest proportion of large pores for foamed phosphogypsum A and B separately reached 17% and 7%, respectively. The water-reducing agents mainly reduced the water consumption of the phosphogypsum slurries; improved the viscosity and shear stress of the slurries; affected the stability of the foam in the gypsum slurries; influenced the pore size and distribution in the foamed phosphogypsum samples; and caused a difference in the strength and dry density of the foamed phosphogypsum samples. The viscosity of the gypsum slurry doped with 0.4% FDN better matched that of the foam; therefore, it had the highest macro-strength and the lowest dry density.

Leaching behavior and release mechanism of pollutants from different depths in a phosphogypsum stockpile

Large phosphogypsum (PG) stacks risk dam failure, with an insufficient consensus on the shear strength parameters for stability analysis. To this end, a combination of scanning electron microscopy and triaxial tests was undertaken to investigate the underlying mechanism between crystal structure and shear strength of in situ and remoulded PG samples. The shear strength and deformation of PG were significantly affected by dissolution and recrystallisation. Dissolution weakened the cementation between particles, leading to a stabilisation of approximate 11 kPa under different confining pressures in the initial shear stage. The hardening phenomenon was related to the formation of cluster crystals under saturated conditions. An increase from 1·57 to 1·73 in the critical state stress ratio on remoulded samples occurred as the K0 consolidation time increased from 4 to 28 days. The compressive deformation of PG is accompanied by chemical consolidation, which is mainly impacted by the consolidation conditions (saturation) rather than the consolidation time. In the engineering design of the PG stacks, ϕ′ could be taken to a higher value at saturation and c′ could be higher when the dry density is higher than 1·2.

The paper discusses the problem of disposal and processing of phosphogypsum dumps as an element of environmentally safe energy- and resource-conserving technologies. The process of impact and possibility of phosphogypsum pre-treatment with weak electric fields to improve its physical and mechanical properties was studied. Two samples of different origin phosphogypsum, which are located in dumps on the territory of the Kamianske City (Ukraine), were used as research material. The research was conducted on samples of the following fractions: 1.0–2.0, 0.4–1.0, 0.1–0.4 mm. Further, balls were formed from the treated phosphogypsum and raw materials to study their compressive strength. The experiment was performed on a pellet strength meter, which operates in the range of 0–2.5 kgf/grain. Phosphogypsum balls, treated with electric current, did not collapse with the maximum values of the device. According to the research results, it was established that preliminary treatment with a low electric current leads to a decrease in the dehydration temperature of phosphogypsum, and the subsequent hydration allows to obtain a material with higher compressive strength properties. This substantiates the potential possibility of involving research results to obtain a cheaper product and will allow to liquidate multi-ton deposits of phosphogypsum.

Environmental assessment of phosphogypsum: A comprehensive geochemical modeling and leaching behavior study

Enhancing the chemical performance of phosphogypsum as a road base material by blending with common aggregates

Two steps leaching process for recovery of rare earths from moroccan phosphogypsum

Optimization of sulfate leaching from Phosphogypsum for efficient bioreduction in a batch bioreactor using a sulfate-reducing microbial consortium

A variety of co-existing impurities in phosphogypsum limit its large-scale and high-value utilization. This paper summarizes the common contents of major impurity components (silicon and phosphorus) and trace impurity components (fluorine, iron, aluminum, and carbon) in phosphogypsum and discusses the harm of impurity components to the comprehensive utilization of harmless phosphogypsum chemical resources. The occurrence status of impurity components in phosphogypsum and the research progress of various impurity removal technologies are summarized, and the effects of these impurity removal technologies on different contents of impurity components are evaluated. On this basis, the goal of improving the whiteness of phosphogypsum samples and the development of technology for further removal of impurities in phosphogypsum to improve the purity of the main content of calcium sulfate are speculated.

Every year, the production of industrial phosphoric acid generates more than 100 Tg of phosphogypsum (PG), leading to significant environmental damage and the occupation of a vast amount of land space. The urgent need to explore applications for PG has become increasingly apparent. However, impurities such as organic substances, slime, phosphorite, and SiO2 reduce the whiteness of PG, making it difficult to utilize for high-value applications. To address this issue, this study employed a two-stage flotation process to remove the majority of impurities, including SiO2, organic substances, and fine slime adhered to the surface of PG particles. The raw PG sample was first sieved to remove some SiO2 particles. After flotation, sulfuric acid and tributyl phosphate were introduced to decompose the PG particles and remove the impurities wrapped inside. Following this flotation combined extraction process, the whiteness of the PG sample improved from 54.1% to 92.9%, meeting the requirements for building walls and filters.

In this article, processes of washing phosphogypsum with water, that formed during obtaining extractive phosphoric acid, by clinker method, from ordinary phosphorite powder (OPP) that is a raw material of Central Kyzylkum were studied. The phosphogypsum formed by washing a sample of phosphogypsum formed in 103% concentration of sulfuric acid without mixing with water, that obtained in the ratio OPP:H2O=1,0:2,5 was found to contain 2,55% P2O5, 29,90% CaO and 42,45% SO3. The acceptable sizes of washing the same phosphogypsum sample have been determined, mixing in different amounts of hot water. Phosphogypsum obtained in acceptable sizes contains 0,75% P2O5, 30,51% CaO and 43,58% SO3. When washing phosphogypsum samples with water, it saves 2.5 times the amount of water and causes to reduce the amount of P2O5 in its composition by at least 3 times. The amount of CaSO4 in the received phosphogypsum sample is increased from 79 to 86%. The samples of phosphogypsum formed without mixing with water and mixing with water were analyzed by X-ray phase analysis and their mutual salt contents were compared.


 
 
 The problem of recycling and storage of phosphogypsum is relevant for many coun- tries of the world, as it is associated with environmental problems such as pollution of water bodies, soil and atmosphere. This study analyzes the possibility of using phosphogypsum for the construction of roads. The objective was a geoecological analysis of the danger of phos-phogypsum stockpiles and a study of the possibility of using phosphogypsum in road construction to solve the problem of its accumulation in the environment. The chemical composition of phosphogypsum samples of the Sumyhimprom and Rivneazot companies was studied using the method of X-ray diffractometry. The content of heavy metals (HM) was analyzed using atomic absorption spectros-copy. An extremely high level of chromium was determined, accounting for more than 20-33 Maximum Concentration Values (MCV). The content of cuprum in the phosphogypsum samples of Rivneazot was 2 MCVs. The contents of other heavy metals did not exceed the MCVs, the synergistic effect should be taken into account. Migration of heavy metals is one of the main problems associated with phosphogypsum stockpiles. The increased acidity of phosphogypsum promotes the formation of soluble HM compounds. Depending on the solubility of toxicants, they accumulate in the ecosystem or migrate, dissolve, and enter plants. The traditional methods of storing phosphogypsum, both from an environmental and economic points of view, are less acceptable than the methods of its recycling and reuse in various sectors of the national economy. The paper theoretically substantiates that the reuse of accumulated phosphogypsum and the implementation of new technological solutions in road construction would reduce the level of technogenic loading that phos- phogypsum imposes on the environment. Based on the analysis of the content of heavy metals and the development of concentration logarithmic diagrams, mobile forms of metals were studied and the harmful effect of metals leaching from phosphogypsum was considered. We determined the positions of toxic substances in the engineering road construction – environment. We recommended dividing hydroxides and hydroxocomplexes of heavy and toxic metals into three groups according to their solubility, having the ability to migrate in acidic, neutral and alkaline environments, respectively. Strict regulations are needed to protect soil cover in areas with acidic soils. We grouped soils on which it is not recommended to use engineered road structures with phosphohypsum due to increased migration of HMs into the ecosystem: sandy; soils rich in humus components, acidic soils (sod-podzolic) or in case of existing proba- bility of an increase in soil acidity (unorganized ingress of industrial waste, acid rain, etc.); acidic soils salinized with chlorides; soils containing ammonia; soils containing sulfates.
 
 

Phosphoric acid manufacturing generates large amounts of phosphogypsum (PG); a by-product generally disposed in the surface or evacuated in the seawater without any pretreatment. Phosphogypsum may host non-negligible amounts of valuable elements such as rare earth elements (REEs), which are critical elements on the global market. Surface disposal of PG may be a sustainable option to allow further processing in order to recover valuable elements. However, surface disposal exposes PG to atmospheric conditions (e.g., water, oxygen) which may increase their reactivity and accelerate the release rate of chemical species. This study aims to evaluate the trace element release rate from PG at atmospheric conditions. The studied PG samples were collected from a Moroccan phosphate treatment plant. The samples were characterized for their (i) chemical composition using inductively coupled plasma optical emission spectrometry (ICP-OES) for major elements and inductively coupled plasma mass spectrometry (ICP-MS) for trace elements; (ii) mineralogical composition by X-ray diffraction (XRD), scanning electron microscope equipped with energy-dispersive spectrometer (SEM-EDS), laser-induced breakdown spectroscopy (LIBS), and the mineral chemical composition was analyzed by electron probe microanalyzer (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS); and (iii) chemical species release rate using leaching tests over 24h at 25 and 60°C. Chemically, the PG samples were mainly composed of Ca (23.03-23.35 wt.%), S (17.65-17.71 wt.%), and Si (0.75-0.82 wt.%), and non-negligible amounts of trace elements: REE (344-349ppm), Cd (3.5-7.4ppm), U (9.3-27.4ppm). Mineralogically, the PGs are mainly formed by gypsum (94.2-95.9 wt.%) and quartz (1.67-1.76 wt.%). In terms of chemical species release, the PGs showed a higher reactivity at 60°C compared to room temperature with a higher release rate at the beginning of the leaching tests. Quantitatively, the PG samples released 3.57-4.11µg/L/day of REE, 3.18-17.29µg/L/day of U, and 1.67-5.49µg/L/day of Cd. Based on the leaching results, we concluded that the trace elements (e.g., U, Cd, REE) are incorporated in PG crystal lattice, which may explain their low concentrations in the leachates. Consequently, total digestion of PG matrix is required to solubilize REE.

Recovery and recycling core of phosphogypsum: Characteristic hazardous elements risk assessment and analysis