Gypsum Calcination in order to Clear Impurities and to Use Phosphogypsum at its Entire Cycle Microbial Bioremediation

Due to the fast improvement of modern industry and agriculture in the twenty-first century, the phosphorus chemical industry has developed at an uncommon rate, creating colossal sums of PG. In expansion to phosphorus, fluorine, natural matter, and other pollutions, dehydrate gypsum (CaSO₄·2H₂O) makes up a noteworthy parcel of its composition. Previous studies have state that for each ton of phosphoric corrosive item created, 4-5 tons of PG are created (Elhaissoufi et al., 2022; Bounaga et al., 2024; Guan et al., 2024). Figure 1 delineates the current surmised yearly generation of PG in diverse nations around the world (Guan et al., 2024). As it were 15% of worldwide generation, PG develops at a rate of almost 1.7 × 108 tons every year. The twenty-first-century quick development of advanced industry and agriculture has brought about in a phenomenal rate of extension for the phosphorus chemical industry, which is presently creating enormous sums of PG. Its composition incorporates dehydrate gypsum (CaSO₄·2H₂O) in noteworthy sums along with phosphorus, fluorine, natural matter, and other pollutions. Four to five tons of PG are delivered for each ton of phosphoric corrosive item delivered, concurring to (Elhaissoufi et al., 2022; Bounaga et al., 2024; Guan et al., 2024). Figure 1 appears the inexact yearly generation of PG in different countries over the world as of right presently (Guan   et al., 2024). PG develops at a rate of roughly 1.7 × 108 tons every year, bookkeeping for as it were 15% of worldwide generation. As a result, PG stack administration and the conceivable natural impacts of their leachates have taken on fundamental significance. Water combined with remaining handled water can create water powered weight, fair like in PG dry stacking, which can cause PG to ended up solvent and cause acidic leakage waters (leachates) to spill into encompassing water bodies and aquifer frameworks (Bilal et al., 2023; Zhou et al., 2023; Salih et al., 2020). Sulfate, extra P, and metals are display in the delivered leachates in expansion to corrosiveness (Salo et al., 2018; Zhou et al., 2023). It was already accepted that sulfates, which make up the larger part of PG (around 50%) along with P, were moderately idle. Be that as it may, inquire about has appeared that they can have negative impacts on sea-going ecosystems (Xie et al., 2022; Zhou et al., 2023). Numerous changes, such as eutrophication that causes an algal sprout. Water quality is affected by oxygen hardship caused by these blossoms (Xie et al., 2022; Zhou et al., 2023; et al., 2025). Besides, the presence of metals (such as zinc, arsenic, and copper) may posture a risk to human wellbeing and the environment (Zhou et al., 2023). Furthermore, a number of metals, counting Cd, As, and Zn, may posture wellbeing and natural dangers (Zhou et al., 2023). Besides, one common issue that needs to be tended to is the nearness of chemical oxygen request (COD) leachate in PG. According to (Bounaga et al., 2023; Ren et al., 2021) the natural compounds connected to PG and microbial action are the source of COD, which builds up in the leachate. For this reason, adequate administration hones are fundamental to address any potential dangers related to PG leachate. The execution of control frameworks by various P businesses has come about in tall corrosiveness and pollution concentrations in the leachate. This has required the advancement of procedures to treat the leachates some time recently transfer or reuse (Pérez-Moreno et al., 2023; Xie et al., 2022; Zhou et al., 2023). According to a few investigate, metals from the PG leachate seem be disposed of along with sharpness, P, and fluoride by including calcium hydroxide (Ca (OH)₂) and spreading antacid substrate (Millán-Becerro et al., 2019). Calcium oxide (CaO) and Barium hydroxide (Ba (OH) ₂) may be utilized to evacuate P, Al, and other pollutes from the PG leachate, concurring to previous study by (Zhou et al., 2023). But more chemical substances may result in distinctive byproducts and raise the by and large taken a toll of the prepare (Salo et al., 2018). On the other hand, viable bioremediation at a moo fetched and with small natural affect can ordinarily be accomplished through the utilize of biotechnological approaches based on the utilize of microbes from adjusted biotopes (Mohammed et al., 2020; Verma and Kuila, 2019). One conspicuous occasion involves utilizing sulfate-decreasing microscopic organisms (SRB), which are recognized for their effectiveness in managing condensed sulfate arrangements, such as a number of wastewaters from mechanical mining (Chai et al., 2023; Ke et al., 2023; Xia et al., 2023). In arrange to accomplish both sulfate decrease and the recuperation of uncommon soil components (REEs), PG leachate has been connected as a sulfate source for sulfate-reducing bacteria (SRB) (Mauk, 2021)

As a result, SRB can moreover be utilized in the organic sulfate expulsion movement (BSRA) of PG leachate bioremediation to expel P, COD, and metals. According to Salo et al., (2018), sulfate-reducing bioreactors may be utilized to expel P and sulfate from leachates PG whereas reducing their acidic nature. The key to protecting the adequacy and solidness of this kind of bioremediation procedure, in any case, is the vague microbial community elements connected to BSRA in PG leachate (Li et al., 2023; Yang et al., 2015; Zhou et al., 2023). As studied before almost the relationship that exists between the expulsion of pollutions and sulfate at the same time, the biochemical composition of the leachate that comes about, and the elements that rise inside the microbial community (Li et al., 2023; Yang et al., 2015; Xie et al., 2022).  This comprises a ponder of their combined impacts on the viability and solidness of the handle of bioremediation, deciding how PG: water proportions affect the filtering handle is the to begin with objective of this work, which points to get it PG's water filtering. To what degree BSRA can be connected to moderate the natural issues caused by the acidic PG leachate is the moment objective (Li et al., 2023; Yang et al., 2015). Utilizing a group sulfate diminishing bioreactor will subsequently optimize the leachate's bioremediation. This will illustrate the relationship between the natural treatment and the expulsion of debasements, as well as the changes in the microbial community structure, pH, broken up oxygen (DO), and Redox potential (ORP) in the leachate, to comprehend the different parts, one can moreover think about the elements of the microbial community. The number of individuals on soil is anticipated to reach 9 billion by 2050, an increment of 0.7% yearly, along with a 70% rise in nourishment request (Roser and Rodés-Guirao, 2013; Elhaissoufi et al., 2022). Giving plants the supplements they require to surrender an adequate edit in a feasible way has long been the point of fertilizer application. Soil nutrients, particularly phosphorus (P) nitrogen (N) and potassium (K) play crucial roles in the growth and development of plants (Vance et al., 2003; Xiong et al., 2018; Sarkar et al., 2018; Scholz and Geissler, 2018; Elhaissoufi et al., 2022). Phosphorus is a significant macronutrient that straightforwardly influences nucleic acids, cell division, and development. These forms all direct protein amalgamation and vitality transmission (Roser and Rodés-Guirao, 2013). This supplement is essential for a wide run of natural forms, such as photosynthesis, vitality generation, redox-homeostasis, signaling, and carbohydrate digestion system (Siedliska et al., 2021; Meyer et al., 2018). Phosphorus is fundamental for root advancement, root characteristic anatomical changes, and root hair thickness (Elhaissoufi, et al., 2020). It may be troublesome for plants to develop ordinarily if there is deficiently phosphorus in the soil or fertilizers. P lack can subsequently lead to critical edit surrender diminishments of up to 15%, claim (Shenoy and Kalagudi, 2005). For this reason, P application remains a crucial rural procedure for assembly plant necessities. Of course, applying water-soluble P fertilizers makes strides the soil's mineral richness and makes more P accessible for plant take-up. According to Meyer (2018), this raises plant surrender and efficiency. P fertilizers are essential for agrarian development and efficiency, but their trim utilize effectiveness may be exceptionally moo since P fixes to soil cations. (Mohammed et al 2023; Shen et al., 2011). P fertilizers, for illustration, can respond rapidly with divalent cations in soil, such as calcium (Ca), iron (Fe), and aluminum (Al), shaping insoluble P mineral shapes in the soil. In this way, moving forward the proficiency of P fertilizer application in connection to trim efficiency and supplement take-up is still exceptionally imperative. RP fertilizers may be a beneficial P shape for trim generation (Elhaissoufi et al., 2022; Millán-Becerro et al., 2019).

Research has appeared that RP dissolvability is the essential figure affecting the positive impacts of coordinate application of RP on soil properties and plant development (Elhaissoufi, W. et al., 2022; Yaqub et al., 2024). In any case, in arrange to meet plant P request in the ions share of agrarian soils, the rate of RP disintegration must be quickened. A promising biotechnological method that has pulled in universal consideration in later decades to boost RP agronomic effectiveness is P-cycling, which employments ergonomically advantageous microorganisms, which have a place to the PGPM bunch and are more commonly known as P solubilizers (PSM) due to their capacity to advance plant development (Elhaissoufi et al., 2022; Abdulrahman et al., 2025; Fatah et al., 2025; Salih et al., 2025; Rahman et al., 2021). It has been illustrated that applying PSB and RP together can increment the agronomic viability of RP since they are both common assets with the intrinsic capacity to solubilize P in soils (Elhaissoufi et al., 2022; Manzoor et al., 2017). It is basic to take advantage of microbial useful characteristics related with P solubilization in arrange to propose microbial-based procedures empowering RP utilize effectiveness, particularly in tall P-retention agrarian soils. Phosphate-based biofertilizers that are both cheap and fitting for both acidic and antacid soils can be delivered by combining PSB and RP, as different test examinations have appeared. Agreeing to (Elhaissoufi et al., 2022; López et al.,2013). The Plant P nourishment for both cereal and vegetable crops was altogether moved forward by the application of RP and PSB, such as Azotobacter, Azosporillum, Rhizobium, and Klebsiella, in combination. To increment RP disintegration and accomplish tall surrender, a Phosphate-solubilizing bacteria (PSB) enhance plant growth by supplying both mineral phosphorus (P) and natural growth-promoting substances. This integrated P biofertilization approach focuses on the combined use of rock phosphate (RP) and PSB for improved agronomic productivity. Previous studies have highlight the importance of co-applying PSB with mineral and organic P to boost agroecosystem production (Elhaissoufi et al., 2022; López et al., 2013; Yaqub et al., 2025). Effective PSB formulations are crucial for P solubilization and bacterial survival. The development of functional and logical PSB screening methods at various levels is essential for creating effective bacterial consortia, thereby enhancing soil amendment and crop inoculation outcomes (Li et al., 2023; Mohammed et al., 2020).

As shown in Figure 1and 2, confirming that P cycling processes in the systems of soil, plants, and microorganisms are shown schematically. Organically bound P found in microbial biomass and plant residues is known as "organic P," while P fixed with soil particles (ions, humus, and primary P minerals) is referred to as "insoluble P." To increase the availability of P, microorganisms and roots use biochemical processes known as extracellular enzymatic hydrolysis and organic acid production (Elhaissoufi et al., 2022).

Figure 1: Interactions of Phosphorus Availability: Sources and Effects on Plant Growth (Guang et al., 2024).

Figure 2: Production in the countries around the world (Guang et al., 2024).

The details of Figure 3, show the changes in BSRA in the center of the project, the sulfate clearing started, demonstrating how long it takes for SRB to adjust to test conditions. The SRB has recently completed a full circle change rate after going through a wide slack organize a few times, which explains the messy delay in BSRA ( Bouargane et al., 2023; Salih et al., 2018). From the thirteenth day onward, there was a slight decrease in the execution between the thirteenth and the twenty-fifth day, with the execution on the twenty-fifth day recovering to a higher level a few days later. The study's findings show that the sulfate reductions reach 78.66%, while the depletion of 1.3 g/L of SO42. Apart from the noted alterations, the sulfate condensation inside the bioreactor generally showed a decreasing trend along the entire thought process. Such alterations are common in bioremediation forms checking SRB and are essentially related to the common elements focusing on the reduction of harmful pollutants. Using the same system, similar plans were successful in an earlier study additionally (Salo et al., 2018; Barrow 2017; Salih et al., 2019) disclosures, which show a BSRA from PG leachates between 60% and 70% and the selection of ambiguous plans in sulfate diminishment flow, demonstrate the unwavering sulfate clearing efficiency in this work. (Salo et al., 2018; Bilal, et al., 2023).

2.1. Impurities Phosphogypsum

Physical techniques such as washing are used in phosphogypsum (PG) purification methods. Although washing effectively removes surface impurities, it produces a lot of wastewater and doesn't address contaminants within the crystal lattice. As an illustration, three-stage countercurrent washing considerably lowers the amounts of soluble phosphorus and fluorine, but it also uses a lot of water and needs to be treated (Guan et al., 2024).  

Particle sizes are the focus of sieving, which purges phosphogypsum of impurities. Over 170 μm and under 25 μm impurities are effectively removed, resulting in 75% purified PG. Chemical and physical techniques improve the removal of impurities (Guan et al., 2024; Hameed et al., 2020 Yassen et al., 2018).  

DISCUSSION

Therefore, the estimation by the PG test shows that there is almost 51% of SO4³? and 24% of Ca, There is 5% F?, 1% P, 0. The amounts of alkalis content are 25% Na, while natural matter content should not exceed 3%. These consistent findings confirm research on the composition of PG, conducted and reported in Tunisia, United States of America, People’s Republic of China, and the Republic of Turkey among other nations, the following ions were detected in minor concentrations in the soil Fe (3 ppm), Al (20 ppm), Mg (24 ppm), Zn (55 ppm), Pb (3 ppm), Mn (2 ppm), Cu (2 ppm), and Cd (6 ppm) (Table below). As such, the total chemical makeup of the PG leachates is contingent upon the type and quantity of PG dissolved in water (Bounaga et al., 2024; Chanouri et al., 2023). As a result, Table 2 shows how the different PG: Water ratios were used to arrange the PG leachates in terms of their chemical composition. There was no significant difference observed in the pH (3.7 and 4.1 ± 0.1) and some of the leachates having higher sulfate condenses, setting from 1.59 g/L to 1.79 g/L. Because the arrangement is totally submerged and the solubility of PG in DW is low and varies from 2.7 to 2.8 g/L, the steady sulfate condensation observed in the effluents—even with raising PG: This means that water proportions is therefore largely determined (Chanouri et al., 2023). The results presented in Table 1 indicate that a PG. Therefore, water ratio of 1:200 enables this solution to filter the highest content of sulfate and pollution from Phosphogypsum and has a filtering productivity of 64%. In this way, compared to the other proportions, the leachate recovered from the 1:200 proportion had higher metal concentrations, counting metals from Cu till Al. Additionally, as Tables 1 and Table 1 show, components that are typically present in PG, to give a metals, were also found in the 1:200 proportion leachate, with concentration values of 516, 443, 12.13, 4.26, and 1 mg/L, respectively. Using ion-exchange water, Salo et al., 2018 provided a detailed comparative chemical composition of PG leachate, with special attention to sulfates, Ca, and P condensation of 1600 mg/L, 641 mg/L, and 10.9 mg/L, respectively. Furthermore, with a P concentration of 16.082 mg/L Chen et al., ( 2020) described in detail the similar chemical composition of a PG leachate that was gathered from a phosphate fertilizer plant in the Guizhou area of China, along with the corresponding concentrations of Cd and As. According to this information, a variety of components and metals are present in the leachate because of the natural makeup of PG and the preparation of the filter caused by water movement (Chen et al., 2020). However, their consolidation in the gem grid (non-solvent stage) of PG explains the moo condensation of metals (Cd, Al, Zn and as) found in the distinct effluent compared to their concentration in crude PG (Akfas et al., 2023). Additionally, the disclose of residual acids from PG, such as fluoric and phosphoric acids, at the filtering handle clarifies the acidic pH (4 ± 0.2) of the resulting PG leachates (Xie et al., 2022). It is imperative to lessen the leachate's sharpness because the buildup of acids filtered from PG can lead to complement (pH < 2), which upsets the environments that are accepting. In addition, although the leachate's concentrations of metals and sulfates were lower than the PG's, they are still considered to be above the safe limit established by the World Health Organization (WHO) for wastewaters, requiring treatment methods before transfer or reuse. This is because metals are hazardous, bioaccumulate, and persistent, which can lead to a range of adverse effects on the environment (Kinuthia et al., 2020; Scholz, 2018; Siedliska et al., 2022).