Phosphate Fertilizer Industry Research Articles

Life cycle environmental and economic assessment of Phosphogypsum utilization in China

Phosphogypsum (PG), a byproduct of the phosphate fertilizer industry, poses significant environmental challenges due to its huge production and complex composition. Efficient and large-scale utilization of PG remains a global issue. China, as the world's largest producer and discharger of PG, faces a relatively low utilization rate and urgently needs effective management strategies. This study evaluates the environmental and economic performance of the main PG treatment pathways in China using life cycle assessment (LCA). The results reveal notable benefits for all three utilization technologies, with sulfuric acid co-production cement (PSC) offering the greatest environmental advantages and β-building gypsum (PBG) providing the highest economic benefits. Scenario analysis suggests PSC as the most effective strategy for achieving dual environmental and economic gains, making it a strong candidate for large-scale implementation. These findings provide critical insights for future PG management strategies in China.

A novel process approach of a circular economy practice in the production of hydroxyapatite from phosphogypsum

Phosphogypsum (PG), a by-product of phosphate fertilizer industry, is chemically impure gypsum (CaSO4 · 2 H2O) containing phosphate residues. Provided by the calcium and phosphorus content, PG can be considered as a precursor for synthetic hydroxyapatite (s-HAp) production. This study proposes a two-step alkali route for s-HAp production from PG. Resulting samples were characterized by ICP-OES, SEM, XRD and FT-IR analyses in comparison with bone ash (BA) sample. Ca/P ratio (wt%) was determined as 2.46 and 2.78 for s-HAp and BA samples, respectively. SEM analysis showed the uniform distribution of spherical shaped particles in BA samples; however s-HAp particles showed irregular distribution of nearly spherical-like particles agglomerated as platelets on the surface. XRD analysis indicated that s-HAp particles possessed low crystallinity and ICDD references showed the appearance of apatite-CaOH phases. FT-IR spectrum showed the vibration bands of PO4 3− bands in the range of 1018–601 cm−1. According to characterization analyses, s-HAp samples show lower Ca/P ratio, irregular morphology, and low crystallinity due to possible impurities. Thus, further downstream operations regarding to impurity removal should be employed to develop a promising route to synthetic HAp production and employ a CE approach on industrial scale to evaluate s-HAp samples as a commercial substitute to BA.

Monitoring dynamics of biocrust rehabilitation in acid-saturated desert soils

The study explores the aftermath of a wastewater reservoir failure in a phosphate fertilizer industry, resulting in the release of acidic water containing phosphorus and sulfate compounds into the Ashalim stream’s Nature Reserve in the Judean desert, which affected the soil surface biological crusts (biocrusts) layer. The study aims to examine contamination effects on biocrusts over 3 years at two research sites along the stream, compare effects between contaminated sites, assess rehabilitation treatments, and examine their impact on soil characteristics. Hypotheses suggest significant damage to biocrusts due to acidic water flow, requiring human intervention for accelerated restoration. The results indicate adverse effects on biocrust properties, risking its key role in the desert ecosystem. The biocrust layer covering the stream’s ground surface suffered significant physical, chemical, and biological damage due to exposure to industrial process effluents. However, soil enrichment treatments, including biocrust components and organic material, show promising effects on biocrust recovery.

Novel Synthesis of Nanocalcite from Phosphogypsum and Cesium Carbonate: Control and Optimization of Particle Size

This study investigates a controlled synthesis and particle size optimization of nanocalcite particles using phosphogypsum, a waste byproduct from the phosphate fertilizer industry, and cesium carbonate (Cs2CO3), a common carbonate source. The effects of synthesis parameters, including temperature and pH, on the size, morphology, and crystallinity of the synthesized nanocalcite particles were systematically examined. The optimized synthesis conditions for obtaining nanocalcite particles with desired properties are discussed. The synthesized nanocalcite particles were characterized using various techniques, such as XRD, FTIR, and SEM, to analyze their crystal structure, morphology, and elemental composition. Particle sizes were determined using the Debye–Scherrer method, and accordingly, nanometric sizes were achieved. The potential applications of the synthesized nanocalcite particles in cementitious materials, agriculture, and drug delivery are highlighted. This research provides valuable insights into the sustainable synthesis and size optimization of nanocalcite particles from phosphogypsum and Cs2CO3 at a controlled temperature and pH.

Smoothing the Phosphorus Resource Stress under the Socioeconomic Development in China.

Phosphorus (P) is the key in maintaining food security and ecosystem functions. Population growth and economic development have increased the demand for phosphate rocks. China has gradually developed from zero phosphate mining to the world's leading P miner, fertilizer, and agricultural producer since 1949. China released policies, such as designating phosphate rock as a strategic resource, promoting eco-agricultural policies, and encouraging the use of solid wastes produced in mining and the phosphorus chemical industry as construction materials. However, methodological and data gaps remain in the mapping of the long-term effects of policies on P resource efficiency. Here, P resource efficiency can be represented by the potential of the P cycle to concentrate or dilute P as assessed by substance flow analysis (SFA) complemented by statistical entropy analysis (SEA). P-flow quantification over the past 70 years in China revealed that both resource utilization and waste generation peaked around 2015, with 20 and 11 Mt of mined and wasted P, respectively. Additionally, rapidly increasing aquaculture wastewater has exacerbated pollution. The resource efficiency of the Chinese P cycle showed a U-shaped change with an overall improvement of 22.7%, except for a temporary trough in 1975. The driving force behind the efficiency decline was the roaring phosphate fertilizer industry, as confirmed by the sharp increase in P flows for both resource utilization and waste generation from the mid-1960s to 1975. The positive driving forces behind the 30.7% efficiency increase from 1975 to 2018 were the implementation of the resource conservation policy, downstream pollution control, and, especially, the circular agro-food system strategy. However, not all current management practices improve the P resource efficiency. Mixing P industry waste with construction materials and the development of aquaculture to complement offshore fisheries erode P resource efficiency by 2.12% and 9.19%, respectively. With the promotion of a zero-waste society in China, effective P-cycle management is expected.

Thermal decomposition mechanism and characterization of phosphogypsum in suspension under multifactor coupling effect

Phosphogypsum (PG) is solid waste generated by the phosphate fertilizer industry. However, by high-temperature thermal treatment, it can be effectively decomposed into byproducts like SO2 and CaO, which are valuable raw materials for the production of sulfuric acid and construction materials, respectively. In this study, we investigated the thermal decomposition properties of suspended PG, as well as the factors governing the PG decomposition procedure. The results show that the PG decomposition rate was influenced by several parameters, with temperature being the most significant, followed by time, atmosphere, and charcoal powder dosing. Similarly, the desulfurization rate was primarily influenced by time, followed by temperature, atmosphere, and charcoal powder dosing. The PG exhibited maximum decomposition and desulfurization rates of 97.73% and 97.2%, respectively, at a calcination temperature of 1180 °C, a calcination period of 15 min, a carbon powder dosage of 4%, and a CO concentration of 6%. Kinetic studies revealed that the activation energy of the PG decomposition reaction decreased from 303.45 to 254.28 kJ/mol as the CO concentration increased from 4% to 6% upon addition of charcoal powder as a reducing agent. Furthermore, higher CO concentrations had a more pronounced effect on lowering the activation energy of PG pyrolysis. When the contents of SiO2 and Al2O3 impurities in the PG content were higher, they reacted with CaO in the decomposition products to produce silicate and aluminate minerals, respectively, decreasing both the CaO content in the product and the PG decomposition rate.

Production of anhydrous hydrogen fluoride from fluorosilicic acid: a review.

Anhydrous hydrogen fluoride (AHF), a critical raw material for industries such as aluminum, pharmaceuticals, and petroleum, has traditionally been sourced from fluorite-a non-renewable mineral. The unsustainable reliance on fluorite has catalyzed the search for alternative AHF production methods. A promising substitute is fluorosilicic acid (FSA), a byproduct of the phosphate fertilizer industry previously deemed waste. Transforming fluorosilicic acid into AHF not only yields a valuable resource but also addresses the environmental and economic challenges associated with waste management. The innovative practice of producing AHF from fluorosilicic acid signals a shift towards sustainable chemical production by capitalizing on waste, potentially diminishing reliance on fluorite and reducing the industry's environmental impact. This review thoroughly dissects the AHF synthesis process from fluorosilicic acid. Despite the acknowledged importance of fluorinated compounds in numerous industrial applications, research on their synthesis from fluorosilicic acid is limited and fragmented. This review seeks to amalgamate this scattered information by closely scrutinizing diverse industrial processing methods. Additionally, it explores the current and future landscape, economic feasibility, and strategies to navigate the obstacles inherent in synthesizing AHF from fluorosilicic acid. It also assesses the environmental impact of these methods, thereby contributing to the dialogue in this emerging field. The primary aim of this manuscript is to foster further research and promote the industrial uptake of this sustainable process. Highlighting the challenges and proposing potential improvements, the review supports the responsible reuse of waste and advocates for advancements in industrial practices.

Assessment of Particulate and Gaseous Fluoride in Phosphate Fertilizer Industry

Fluorides are emitted in both gaseous and particle forms in the industrial sector. However, studies usually only report total fluoride content. Therefore, the study aimed to assess the particulate, gaseous fluoride and correlate it with the respirable dust particles in Single Super Phosphate (SSP), Granular Single Super Phosphate (GSSP), and administration divisions of the industry. Respirable dust particles, particulate fluoride, and hydrogen fluoride in the work environment were collected on a filter cassette containing an MCE filter paper (0.8 micron 37-mm) and Na2CO3 impregnated backup pad, respectively, using a personal sampler. The fluoride samples were analyzed using Ion Selective Electrode (ISE) and expressed as milligrams per meter cube (mg.m-3). The respirable dust, particulate, and gaseous fluoride content were found to have statistically significant differences (p<0.001) between the divisions (SSP, GSSP, and administration) in the static monitoring, whereas, in the case of personal monitoring, no significant differences were observed. Average airborne respirable, particulate, and gaseous fluoride levels in static monitoring were 1.37, 1.03, 0.20 mg.m-3, 0.018, 0.008, 0.001 mg.m-3, and 0.808, 0.403, 0.026 ppm in SSP, GSSP and administration respectively, whereas in personal monitoring the average respirable, particulate and gaseous fluoride concentrations were 1.18, 0.85, 0.30 mg.m-3, 0.0013, 0.007, 0.002 mg.m-3 and 0.356, 0.258, 0.011 ppm in SSP, GSSP and administration respectively. The present study observed that the levels of fluoride decreased with an increase in distance from SSP, followed by GSSP and administration. It indicates that the fluoride exposure was inversely proportional to the distance of the source. This study outcome will help to design a policy and intervention to mitigate fluoride exposure among workers.

Towards circular and sustainable restoration of a deeply polluted river basin: The Odiel River catchment (SW Spain)

The Ría de Huelva estuary located in SW Spain is heavily polluted by acid mine drainage leachates and phosphate fertilizer industry effluents. This study assesses the effectiveness of a solid waste rich in calcite originated during the remediation of industrial effluents using the passive dispersed alkaline substrate (DAS) technology, for the treatment of highly acid and polluted mine drainages. The research consists of flowing the mine leachates through a column loaded with a combination of an alkaline reagent (i.e., calcite-rich waste resulting from the treatment of industrial leachates) scattered in a non-reactive matrix (i.e., wood chips) to increase the pH of acidic water while decreasing the solubility of dissolved pollutants. The alkaline treatment achieved average removal percentages of 100 % for Al and Fe, and close to 90 % for Cu. However, the treatment was not effective for other metals present in mine drainages such as Co and Ni. These results are comparable to those achieved in the DAS treatment with commercial limestone. The precipitation of oxyhydroxysulfates (i.e., schwertmannite and basaluminite) and carbonates (i.e., malachite and hydrozincite) minerals could be controlling the solubility of pollutants during the treatment. The solid wastes from the DAS treatment were subjected to two standardized leaching tests (EN 12457-2 from the European Union and toxicity characteristic leaching procedure (TCLP) from the United States) in order to ensure suitable management and avoid potential environmental impacts. According to European Union legislation, the high mobility of Cu, Zn and SO4 confers some solid wastes from the DAS treatment the hazardous waste classification. However, according to United States regulation, these same solids are considered non-hazardous wastes. This research could help to improve the environmental sustainability of acid mine drainage treatment with DAS technology by replacing marketable limestone with a low-cost alkaline waste.

Facile synthesis of neodymium vanadate nanoribbons and its application to highly efficient determination of cadmium ions

AbstractBACKGROUNDCadmium ions may be discarded to the environment with living organisms from fossil fuel combustion, phosphate fertilizer and battery industries. It is urgent and essential to develop a sensitive and rapid method for monitoring Cd2+ level in aquatic environments and biological systems. Neodymium vanadate possesses good catalytic performance for the electrocatalysis of heavy metal ions. Single crystalline Nd vanadate nanoribbons were obtained by a facile approach and used as electrode materials for electrochemical detection of Cd2+.RESULTSThe Nd nanoribbons with tetragonal NdVO4 phase possess length, width and thickness of longer than 10 μm, 200 nm to 1.5 μm and 50 nm, respectively. Nd vanadate nanoribbons can serve as a good electron transfer interface. An anodic peak is located at +0.56 V at the Nd vanadate nanoribbon‐modified electrode in 0.1 mol L−1 KCl electrolyte containing 1 mmol L−1 Cd2+ by square wave voltammetry technique. The Nd vanadate nanoribbon‐modified electrode exhibits a linear range of 0.01–1000 μmol L−1 and a detection limit of 0.29 nmol L−1, with good stability, reproducibility and selectivity for Cd2+ detection.CONCLUSIONThe optimal measurement conditions including the pH value of the KCl solution, deposition time, deposition potential and standing time, which are pH 1, 180 s, −1.0 V and 60 s, respectively. The Nd vanadate nanoribbon‐modified electrode shows great application potential for detecting heavy metal ions in liquid environments. © 2023 Society of Chemical Industry.

Potassium-phosphorus-sulfur augmented biochar production from potentially toxic elements abated gypsum pond wastewater of phosphate fertilizer industry

Present study highlights scope and process for production of environmentally safe (reduced F, Cr, Cd content) and multi-nutrient (K, P, S) enriched biochar utilizing highly acidic gypsum pond wastewater (GPW; P and S rich) and banana peduncle (K rich) waste. Untreated and treated [potentially toxic elements (PTE) adsorbed on Crassostrea shells] GPW soaked biomass pyrolyzed at 400, 600, 800 °C and produced K-P-S enriched biochar (KPS-B-400/600/800 and T-KPS-B-400/600/800). Physicochemical characteristics of biochar were investigated by XRD, FTIR and surface area analyser. The K, P and S contents were 14–15.53, 1.88–2.27 and 3.75–4.77% in the untreated biochar produced at 400, 600 and 800 °C respectively, with corresponding values of 15.21–18.43, 2.05–2.91 and 0.62–1.09% in the treated biochar. At various temperatures, K, P and S formed mineral phases such as K(H2PO4), KH5(PO4)2, K2CaP2O7 and K2SO4 in untreated biochar, and K3P, K2SiP2 and K2S in treated biochar. Sulfite (SO32-) was identified as pre-dominant functional group in untreated and treated biochar. Water soluble and Toxicity Characteristic Leaching Procedure (TCLP) F contents in T-KPS-B-800 were lowered to 0.005% and 0.013% respectively and values were well below permissible limits. Toxic Cd TCLP content reduced by 5.75% in T-KPS-800 over KPS-800, whereas Cr reduction of 44% was eastimated in T-KPS-400 with respect to KPS-400 due to treatment of GPW with molluscan shells. Above findings establish an alternative way of nutrients recovery and PTE reduction from phosphate fertilizer industry GPW.

Does phosphogypsum addition affect phosphate rock dissolution in acid soils?

The direct application of phosphate rock (PR) has been found suitable for acidic soils. Still, efforts are needed to improve its reactivity to match grassland P demand. This research aimed to investigate changes in the dissolution of two Moroccan sedimentary PRs (Ben Guerir and Khouribga) in response to four rates of phosphogypsum (PG)—a by-product of the phosphate fertilizer industry. We conducted a 60-day incubation study using two acid soils from New Zealand. The soils were treated with PRs at 100 mgP kg−1 of soil either alone or combined with PG, which was applied at 0, 1, 3 and 9 t ha−1 (approximately the equivalent of 0, 0.9, 2.7, and 8.1 g of PG kg−1 of soil, respectively). The dissolution rates were determined from the differences in residual calcium (Ca) extracted with 1 M HCl. Soil pH, Olsen P, exchangeable aluminium (Al) and Ca and Ca saturation were analyzed at the end of the experiment. Phosphate rocks and PG’s physicochemical properties were characterized. Phosphogypsum addition increased Olsen P by 34% and 59% at 9 t ha−1 compared to 0 t ha−1 in Molesworth and Lindis Peaks soils, respectively. However, PG did not affect the dissolution of PRs in the different of soil types. Khouribga PR was more reactive than Ben Guerir PR, especially in the Molesworth soil where soil pH and base saturation were lower and P retention was higher compared to Lindis Peaks soil. Particle size distribution was the key factor that contributed to the observed greater reactivity of the Khouribga PR. Both PRs showed dissolution rates >50%, suggesting their suitability for direct application on acid soils. Being an important source of sulphur and some P, PG if combined with PR, can promote and complement PR’s direct use as fertilizer on acid soils. Moreover, the development of new fertilizer products by combining these two materials should be encouraged.

Immobilisation of contaminants by ‘green’-synthesized magnetite as a remediation approach to the phosphogypsum waste leachates model solution

Contaminant removal from (waste)waters by magnetite is a promising technology. In the present experimental study, a magnetite recycled from the steel industry waste (zero-valent iron powder) was used to investigate the sorption of As, Sb and U in phosphate-free and -rich suspensions, i.e. as a remediation for the acidic phosphogypsum leachates derived from the phosphate fertilizer industry. The results showed up to 98% U removal under controlled pH conditions, while phosphate did not hinder this immobilisation. In contrast, the results confirmed the limited uptake of As and Sb oxyanions by magnetite in presence of phosphate as the competing anion, displaying only 7–11% removal, compared to 83–87% in the phosphate-free sorption experiments. To limit this wastewater problem, raw ZVI anaerobic oxidation was examined as mechanism to increase the pH and as a source of Fe2+ in a first step, and in a second step to remove phosphate via vivianite precipitation, therefore prior to the reaction with magnetite. UV–Vis, XRD and SEM-EDS showed that vivianite precipitation is feasible at pH > 4.5, mainly depending on the phosphate concentration. The higher the [PO43−], the lower is the pH at which vivianite precipitates and the higher the % removal of phosphate from solution. It is anticipated that an optimum 3-steps design with separate reactors controlling the conditions of ZVI oxidation, followed by vivianite precipitation and finally, reaction with magnetite, can achieve high contaminant uptake in field applications.

Examination of the environmental behavior of phosphogypsum with the application of lab-scale experiment

Phosphogypsum (PG) is a reject of the phosphoric acid production process in phosphate fertilizer industries. The process results in the production of relatively large quantities of PG that it might cause serious environmental and human health concerns. The data of a laboratory investigation of PG are presented here. Lab-scale experiments with lysimeters were conducted in order to simulate and examine the environmental characteristics and the temporal behavior of PG leachates in terms of physicochemical characteristics and chemical composition. Based on the results, leachates from already deposited for many years PG or its mixture with marble powder, seemed to have better pH and conductivity values and lower elemental concentrations compared to leachates from freshly disposed PG. However, the leachates characteristics improve and stabilize in both cases after four days of irrigation or of 1080–1240 mm of rain. Most major elements were found to have minimal leachability, and the material satisfied the environmental limits for its disposal at landfills for inert and non-hazardous wastes.

Investigating effects of phosphogypsum disposal practices on the environmental performance of phosphate fertilizer production using emergy analysis and carbon emission amounting: A case study from China

The phosphate fertilizer industry faces increasing environmental pressures related to phosphogypsum disposal. It is necessary to explore the impact of different phosphogypsum disposal schemes on the comprehensive performance to promote sustainable development in this industry. We propose a comprehensive approach based on emergy analysis and carbon emission accounting to compare the impacts of different phosphogypsum disposal schemes on phosphate fertilizer production in terms of environmental sustainability, pollutant emission impacts, carbon emission intensity, and their synergistic effects. As a case study, a monoammonium phosphate production enterprise (phosphogypsum storage, Scenario 1) in Hubei Province and three other scenarios based on different phosphogypsum resource utilization practices (Scenario 2: monoammonium phosphate production + phosphogypsum manufacturing building materials; Scenario 3: monoammonium phosphate production + phosphogypsum manufacturing fertilizer filling materials; and Scenario 4: monoammonium phosphate production + phosphogypsum manufacturing cement retarder) were investigated using the proposed approach. The results show that the three phosphogypsum resource utilization practices could enhance the synergistic effect of the integrated system to different degrees relative to Scenario 1 by improving the energy-use efficiency and/or reducing the impact of pollutant emissions. Scenario 3 had the best synergistic effect, followed by scenarios 4, 2, and 1. The three phosphogypsum reuse practices enhanced carbon emission intensity to varying degrees compared with Scenario 1 due to the increasing fossil energy use. Those phosphogypsum reuse practices, based on nonrenewable resources/energy source inputs, caused conflict between waste reduction and carbon emission reduction. This study helps construct an integrated approach for thoroughly investigating the environmental performance of an integrated system consisting of phosphate fertilizer production and phosphogypsum disposal, thus providing a decision-making tool for the phosphate fertilizer industry. We also present targeted decision-making information for phosphate fertilizer production in China.

Utilization of Industrial Waste Phosphogypsum as Geomaterial: A Review

Phosphogypsum (PG) is a waste product of phosphate fertilizer and phosphoric acid industries. Vast quantities of the waste product are generally left stockpiled on the ground or discharged into rivers or ponds, and pose serious environmental concerns. Several countries are facing problems with the handling, storage, and utilization of PG. This article is a comprehensive review of the physicochemical, microstructural, geotechnical, radiation, and leaching characteristics of raw PG. The performance of PG with other admixtures (cement, fly ash, lime, ground granulated blast furnace slag) and soils (clays, loess, sands) has also been reviewed. In addition, the factors, such as pH, calcination, forms of PG, and curing methods, that affect the geotechnical, durability, and leaching characteristics of PG mixtures are also discussed. Based on the review, it has been observed that raw PG has high sulfate content, high water absorption capacity, and high variability in strength, leaching, and radioactivity properties; thus, using raw PG alone as a backfill or embankment material is not suitable. However, the geotechnical, durability, and leaching properties of PG may be enhanced by using it in combination with other admixtures. The excessive usage of PG should also be undertaken with caution, as the higher amount of PG may lead to a decrease in the strength and the formation of cracks. There are studies that have reported the optimum content of PG; however, the range is quite varied and can differ for soil types. Therefore, it is recommended to investigate the optimum content of PG before the start of any road or ground improvement project. The compaction characteristics of PG-admixed soils are highly contrasting and hence need more comprehensive studies. The strength characteristics and resilient modulus are also highly variable and hence need more exhaustive research for actual usage of PG in road construction. Other critical issues that require attention have been highlighted, and associated research gaps that could be explored in future research works have been identified.

Effects of phosphogypsum substitution on the performance of ground granulated blast furnace slag/fly ash-based alkali-activated binders

Phosphogypsum (PG) is a byproduct of the phosphate fertilizer industry. Using PG waste to produce environmentally friendly building materials is becoming a desirable waste recovery method. However, unprocessed PG contains impurities, which often impedes its application in the construction industry. Considering that PG can provide Ca2+ and SO42− to a reaction system, this study develops an economic and environmental approach for optimizing the performance of PG-based alkali-activated binders (PGAABs) based on the combined use of PG, ground granulated blast furnace slag (GGBFS) and fly ash as precursors. An experimental investigation was carried out to understand the effects of PG content, Na2O content (M+) and alkali modulus (AM) on the properties of fresh and hardened PGAABs. The X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) results showed that using PG as a partial substitute for GGBFS in the precursors facilitated the alkali-activated reaction. The compressive strength of PGAABs cured at room temperature increased with increasing PG content, while the setting time decreased with increasing PG content. Compared with the specimen without PG, the PGAABs required lower activator doses to obtain high compressive strengths. Leaching results also confirmed that using PGAAB with 10% PG content can result in cost-related and environmental benefits.

Efficient precipitation of soluble phosphorus impurities in the recycling of phosphogypsum to produce hemihydrate gypsum

Phosphogypsum (PG), a waste product of the phosphate fertilizer industry, is a source of environmental pollution. PG can be calcined to form the hemihydrate gypsum (β-CaSO4•0.5H2O, HPG), making it a potential substitute to natural gypsum. However, PG contains large amounts of soluble phosphorus(P) impurities, which pose a serious risk on the soil and groundwater, especially when they are abundantly accumulated and leached. This study systematically investigated that the pretreatment of PG by calcium hydroxide (CH) solution. Inductively coupled plasma optical emission spectroscopy (ICP) and X-ray diffraction (XRD) were used to study the precipitation of soluble P impurities in PG, differential thermal analysis (DTA) and BET (Brunauer-Emmett-Teller) were used to study the effect of CH solution on the physicochemical property of PG. In addition, the hardening characters and hydration process of HPG after stabilization with CH solution were studied in detail. The results show that pretreatment with CH solution can stabilize the soluble P impurities. However, the addition of CH solution can slightly reduce the mechanical properties of HPG and prolong the setting time. This was attributed to the production of excess CaHPO4·2H2O, which encapsulates the HPG. It is concluded that pretreatment of PG with 0.05% CH solution reduce environmental pollution without affecting the properties of the HPG produced.

A Sustainable Composite Cementitious Material Manufactured by Phosphogypsum Waste

The phosphogypsum is a by-product of the phosphate fertilizer industry. It has accumulated over several decades, and not only takes up a large amount of land, but also poses a significant risk to the environment and resource waste. In order to promote the use of phosphogypsum, its hydration hardening characteristics are studied using a scanning electron microscope, X-ray diffractometer and mercury intrusion porosimeter. When the amount of phosphogypsum is increased, a decreasing trend in the reaction degree, non-evaporable water and portlandite is observed. Among them, the reaction degree and non-evaporable water, flexural strength and compressive strength reached their maximum when the content of phosphogypsum was 10%, which were as follows: 22.34 %, 21.13 %, 9.02 MPa and 49.8 MPa, respectively. Meanwhile, phosphogypsum can participate in the secondary hydration reaction in the system and act as a microaggregate. The addition of no more than 30% phosphogypsum can enhance mechanical characteristics, reduce porosity, refine pore size distributions and densify the microstructure. The findings of this study may aid in the production of phosphogypsum-based composite cementitious materials with superior performance, thereby promoting phosphogypsum recycling and protecting the environment.

Biological Monitoring of Urinary Fluoride Among Phosphate Fertiliser Production Industrial Workers

Objectives: Fluoride pollution at the workplace environment arises mostly due to anthropogenic activities. The workers working in phosphate fertilizer industry might have chronic exposure to excessive fluoride which can cause adverse health effects. Therefore, the present study was designed to assess urinary fluoride levels in occupationally exposed workers. Methods: In this study, pre and post-shift urinary samples were collected from phosphate fertilizer industry male workers (n=53). Fluoride levels in urine samples were analysed using an Ion Selective Electrode (ISE). Findings: The mean concentration of pre-shift and post-shift urinary fluoride levels were 2.141.35 and 2.422.02 mg/g of urinary creatinine respectively. Workers’ pre-shift mean urine fluoride levels were categorised according to their working departments. Workers from the manufacture plat of Single Super Phosphate (SSP), Granular Single Super Phosphate (GSSP), maintenance, and administration had fluoride levels of 2.871.88, 2.431.01, 2.161.30, and 0.920.601 mg/g of urine creatinine, respectively. Similarly, the post-shift urinary fluoride levels were 3.683.00, 2.641.85, 2.241.78 and 1.140.53 mg/g of urinary creatinine in these departments respectively. One-way analysis of variance shown significant difference in urine fluoride concentrations between pre-shift (ANOVA, df=3, F=4.717; p=0.006) and post-shift samples (ANOVA, df=3, F=2.895; p=0.044). About 22.64 % of subjects in the pre-shift and 3.77% of subjects in the post-shift had exceeded the urinary fluoride limits prescribed by various statutory agencies. Novelty: Based on pre-shift and post-shift work exposure assessments, this study adds new knowledge to scientific research on the fluoride exposure among phosphate fertiliser sector workers. While there is sporadic information on fluoride levels among various other occupational groups, very few reports reported the fluoride levels in fertilizer industryworkers. Outcomes of this study will help to identify the source of fluoride and extent of fluoride exposure so as to suggest the mitigation measure to control fluoride exposure at occupational settings. Keywords: Biological monitoring; Fluoride exposure; Urinary fluoride; Occupational fluoride exposure; Fertilizer industry workers