Phosphoric Acid Production Research Articles

Simultaneous removal of phosphorus and organic contaminants from phosphogypsum using hydrothermal method for gypsum resource regeneration

Phosphogypsum (PG) is a common chemical by-product from wet process phosphoric acid production, accumulated stockpiles of 300 million tons in China. The challenge for the comprehensive utilization of PG is thorough removal of phosphorus and organic contaminants from PG, which inevitably entails the loss of overall whiteness and limits its utilization in building materials and other fields. This work investigated the speciation of phosphorus and organic contaminants in PG by FTIR spectroscopy, Raman spectroscopy, XRD, SEM-EDS and GC-MS. On this basis, by using K2S2O8 as a mineralizer, PG was transformed into anhydrous calcium sulfate powder and the organic contaminants were fully decomposed (removal rate >80%, with residual TOC of 0.078%) under hydrothermal treatment. Under optimal hydrothermal conditions (0.3 M K2S2O8, heated at 120 °C for 12 h), the whiteness of product significantly improved from 40.9 to 97 and effective removal of phosphorus was achieved (more than 76%). The residual phosphorus in treated PG was 0.108%, which met the standard of PG as a building material in China GB/T-23456 2018 (P content < 0.2%). The mechanism study revealed that the phase transformation of calcium sulfate from dihydrate to anhydrous played a dominant role in the removal of phosphorus, H+ and SO42- from K2S2O8 decomposition facilitated the dissolution-recrystallization process of calcium sulfate, allowing the phosphorus in the lattice to escape. In addition, by thermal activation, K2S2O8 generated free radicals of SO4•- and OH• dissipated the organic contaminants in PG. This work provides theoretical and practical bases for the harmless disposal and resource recycling of industrial by-product gypsum, and it is of great significance to build the "zero-waste city".

HT-TPP: A Hybrid Twin Architecture for Thermal Power Plant Collaborative Condition Monitoring

Thermal power plants, TPP, are one of the main players in the phosphoric acid and fertilizer production value chain. The control of power plant assets involves considerable complexity and is subject to several constraints, affecting the asset’s reliability and, most importantly, plant operators’ safety. The main focus of this paper is to investigate the potential of an agent-based digital twin architecture for collaborative prognostic of power plants. Based on the ISO 13374:2015 scheme for smart condition monitoring, the proposed architecture consists of a collaborative prognostics system governed by several smart DT agents connected to both physical and virtual environments. In order to apprehend the potential of the developed agent-based architecture, experiments on the architecture are conducted in a real industrial environment. We show throughout the paper that our proposed architecture is robust and reproduces TPP static and dynamic behavior and can contribute to the smart monitoring of the plant in case of critical conditions.

Potential uses of phosphogypsum: A review

Phosphogypsum (PG) is a by-product of the phosphate fertilizer industry that is produced during the phosphoric acid production process. Annual global PG production ranges between 100 to 300 Mt, with only 15% of that utilized while the rest is usually placed on large dumps with potential serious human and environmental impacts. The aim of this study is to give an overview and to evaluate the existing and potential uses of PG that extend from soil stabilization to cement and chemical industry and for agricultural to geotechnical, human impacts, and environmental applications. More specifically, PG can be used as a substitute in the cement industry, in building materials and in road construction, as a fertilizer for soil improvement, as a raw material for the production of some chemicals, and as a backfilling material for the rehabilitation of abandoned mines and quarries, while the recovery of gypsum and the extraction of rare earth elements signifies the potential importance of PG to cyclic economy. The paper offers an extensive overview of existing and potential uses of PG, discusses their adequacy, and reveals that PG can be widely used under certain conditions, rather than disposed as waste in stockpiles.

Experimental Study on the Road Performance of High Content of Phosphogypsum in the Lime–Fly Ash Mixture

Phosphogypsum (PG), as a by-product of the production of phosphoric acid, faces the problems of large annual output and difficult treatment. There is a large demand for fillers in the process of road paving, which may be an effective method for the utilization of PG resources. In this study, three proportions of phosphogypsum–lime–fly ash (PLF) mixture were designed, first, according to orthogonal tests. The comprehensive performance of the PLF mixture was tested by the compression rebound modulus test, unconfined compressive strength test, flexural tensile strength test, dry shrinkage test, and temperature shrinkage test, respectively. The results show that adding crushed stone to the PLF mixture can effectively improve the compression rebound modulus, unconfined compressive strength, and flexural tensile strength. The high content of PG in the mixture can also improve the dry shrinkage and temperature shrinkage properties of the mixture. According to the road layer requirements, the optimum proportion of the PLF mixture is recommended, which may benefit the road construction and PG resources.

Influence of Aluminum on Morphologies and Crystallization Kinetics of Hemihydrate Calcium Sulfate in the Hemihydrate Process of Phosphoric Acid Production

The influence of aluminum on morphologies and crystallization kinetics of hemihydrate calcium sulfate (HH) in the hemihydrate process of phosphoric acid production was investigated. X-ray diffraction analyses showed that Al3+ ions can be adsorbed onto the crystal surface and incorporated into the crystal lattice. The crystal growth rate first increases and then decreases due to the dual role of Al3+ ions in a mixed suspension mixed product removal (MSMPR) crystallizer. For the first time, the effect of Al3+ ions on nucleation kinetics of HH at 93 °C was investigated by focused-beam reflectance measurement (FBRM). The results indicate that Al3+ ions retard the nucleation by increasing the interfacial tension values (γ).

Deep removal of phosphorus and synchronous preparation of high-strength gypsum from phosphogypsum by crystal modification in NaCl-HCl solutions

Phosphogypsum (PG) is a bulk solid waste that is generated during the production of wet-process phosphoric acid. Presently, the impurities (especially co-crystalline phosphorus impurities) and low value-added recycling products restrict the utilization of PG. In this study, the complete deconstruction of co-crystalline phosphorus encapsulated in gypsum lattices was realized through phase transformation from PG to α-hemihydrate gypsum (α-HH) in NaCl solutions, which was the key to efficiently eliminating phosphorus impurities from PG. Simultaneously, the addition of HCl into NaCl solutions could fully dissolve the phosphates released from gypsum lattices and distinctly increase the phosphorus leaching efficiency. Moreover, synergistic regulation of crystal morphology and particle size of α-HH was obtained in NaCl-HCl solutions by crystal seed induction, and regular large-grained α-HH with small specific surface areas was prepared, which weakened the phosphorus adsorption on the product surfaces and further improved the leaching efficiency. Importantly, the prepared α-HH were high-strength gypsum with high added value. Consequently, deep phosphorus removal (>99%) and synchronous preparation of high-strength gypsum (>30 MPa) with high added value from PG was achieved by regulating the phase transition from PG to α-HH and controlling the α-HH morphology and size by crystal seed induction in mixed solutions of NaCl and HCl under mild conditions. This work provides instructive guidance for efficient impurity removal and high value-added utilization of industrial byproduct gypsum at low cost.

Influence of Impurities on the Process of Obtaining Calcium Carbonate during the Processing of Phosphogypsum.

The article is devoted to the study of the influence of residual sulfuric and phosphoric acids on the process of processing large-tonnage phosphogypsum (PG) waste into calcium carbonate. In the Russian Federation, about 10 percent of existing phosphogypsum waste is processed into construction materials. Acidic impurities (phosphoric and sulfuric acids) in their composition are an obstacle to the use of phosphogypsum for the production of binders. This study finds that impurities also reduce the chemical activity of phosphogypsum. At the same time, the paper focuses on the potential of phosphogypsum for the production of calcium carbonate. This article investigated the amount of impurities in phosphogypsum. The results show that during automatic washing of phosphogypsum, losses are approximately 30–35 wt. %. It was also found that phosphogypsum by 22% consists of impurities of phosphoric and sulfuric acid. These acids are characteristic waste products of extraction phosphoric acid (EPA) production. By ASTM C471M-20ae1, the content of calcium sulfate dehydrate and hemihydrate before and after washing was determined. A thermodynamic calculation of the proposed interaction of phosphogypsum with carbonates showed that the characteristic reaction is possible. The conversion process of phosphogypsum to get the corresponding calcium carbonate was carried out at 70 °C. Data on the chemical composition of the reaction products, obtained by X-ray fluorescence analysis on a Shimadzu EDX-7000 spectrometer, showed that some reactions proceed incompletely and need the selection of optimal conditions. The potential commercial benefits of processing phosphogypsum by carbonization were defined for products such as calcium carbonate or its derivatives.

Development of technology for processing solid waste from the production of orthophosphoric acid into an inorganic composite material

The article considers the processes of processing solid waste from the production of phosphoric acid - phosphogypsum - into composite inorganic materials. It is shown that heat treatment at a temperature of 1073 K leads to the formation of inactive calcium sulfate. Carrying out the heat treatment process under similar conditions in the presence of an organic reducing agent is accompanied by the formation of a composite material with a luminescent ability. A simple method for the disposal of large-tonnage production waste with the production of a demanded product is proposed.

Utilization of Fenton oxidation approach in wet phosphoric acid process for mitigating foam generation

Significant amounts of foam generated during the production of phosphoric acid would severely occupy the head space in the reactors, thereby reducing output capacity dramatically. Here, we first proposed a green and clean approach based on Fenton oxidation theory to mitigate the generation of foam. The effect of H2O2 dosage, FeSO4 dosage, and pH value on the defoaming performance were investigated systematically. Moreover, the defoaming performance between Fenton oxidation process and traditional defoamer were compared and the defoaming mechanism was described with the help of XRD analyses. The results obtained from the Fenton oxidation process demonstrate that the use of H2O2 in conjunction with FeSO4 are beneficial to mitigating the foam generation, and the defoaming performance is positively correlated to the dosage. Furthermore, Fenton oxidation process outperforms than that of traditional defoamer in terms of reducing foam generation. The defoaming mechanism is ascribed to the fact that the organic substrates existing on the phosphate concentrate surface could be completely decomposed and the soluble carbonate minerals were prone to being dissolved during the regulation of pH value, thereby inhibiting the production of CO2 gas. This work is helpful in providing guidance for utilizing a green and clean approach based on advanced oxidation theory to mitigate the foam generation during the wet phosphoric acid process. More importantly, it provides a theoretical basis for optimizing this type of processing methods.

Thermal properties and pyrolysis kinetics of phosphate-rock acid-insoluble residues

In the phosphorous–sulphur two-step process for the clean production of phosphoric acid, a phosphate-rock acid-insoluble residue (PAIR) is a solid filter residue obtained via the phosphoric acid acidolysis of phosphate rock (PR). PAIR combined with other raw materials can be used to prepare cement, ceramics and glasses, opening a potential avenue for large-scale PAIR utilisation. However, the preparation of such materials requires high-temperatures calcination. Understanding the high-temperature thermal properties of PAIR can enable its more targeted comprehensive utilisation or disposal. In this study, the thermal properties and pyrolysis kinetics of PAIR were systematically studied using a multiple heating rate method based on thermogravimetric analysis and a kinetic model. Results showed that from room temperature to 1200 °C, the main changes in the PAIR were the complete removal of fluorine and sulphur, partial removal of phosphorus and conversion of quartz to cristobalite. Moreover, during these processes, H2O(g), NH3, N2, CO2, SO2, P2O5(g), CO, CF3+ and organic gases were volatilised. Herein, the pyrolysis kinetics of PAIR is divided into five stages. Stage 1 (conversion rate ɑ: 0.05–0.2) conforms to the random nucleation and growth as well as the Avrami–Erofeev (n = 2/3) mechanism; the corresponding mechanism function is F(ɑ) = [−Ln(1 − ɑ)]2/3. Stage 2 (ɑ: 0.2–0.4) conforms to the first-order chemical reaction mechanism; the corresponding mechanism function is F(ɑ) = −Ln(1 − ɑ). Stage 3 (ɑ: 0.4–0.6) conforms to the phase boundary–controlled reaction and one-dimensional movement mechanism; the corresponding mechanism function is F(ɑ) = ɑ. Stage 4 (ɑ: 0.6–0.8) conforms to the three-dimensional diffusion process (Jander model); the corresponding mechanism function is F(ɑ) = [1 − (1 − ɑ)1/3]2. Stage 5 (ɑ: 0.6–0.95) conforms to the one-dimensional diffusion process; the corresponding mechanism function is F(ɑ) = ɑ2.

Sustainable purification of phosphoric acid contaminated with Cr(VI) by Ag/Ag3PO4 coated activated carbon/montmorillonite under UV and solar light: Materials design and photocatalytic mechanism

Wet production of phosphoric acid, the most used low-cost industrial approach, first leads to an impure phosphoric acid contaminated by organic and heavy metal pollutants which requires costly purification before its usage. The present work has investigated for the first time the recovery of Cr(VI), one of the most co-existed heavy metals, from the phosphoric acid medium. For this purpose, three composites based on Ag3PO4 coated on Montmorillonite (MAg3PO4), commercial activated carbon (ACAg3PO4), and synthetic activated carbon (SACAg3PO4) were fabricated. The photocatalytic reduction of Cr(VI) was studied comparatively in the absence and presence of citric acid as a hole scavenger under UV and solar light irradiations. Under UV light, MAg3PO4 was the most efficient, while activated carbon-based photocatalysts showed higher reduction rates under solar light due to the photosensitizing effect. Compared with an aqueous medium, the photocatalytic reduction was very effective without citric acid in a phosphoric acid medium because of the low photogeneration of reactive oxygen species (ROSs). The chemical bonds formed between Ag3PO4 and support materials, as proved by XPS, may boost the photocatalytic activity due to enhanced charges of photogeneration and separation. SACAg3PO4 showed higher reduction ability even at higher Cr(VI) concentrations (100–300 ppm). A comparison study showed that SACAg3PO4 is more effective than as-prepared ACTiO2. This investigation shows promising findings to widen the application of photocatalytic technology in different industrial fields.

Rheological behaviour modelling of phosphoric acid produced from Moroccan phosphate rocks

ABSTRACT Rheological behaviour of the industrial phosphoric acid is considered as one if not the most important factor that affects the performance and profitability of phosphoric acid production in wet process facilities. This work is focused on studying and modelling the rheological behaviour of phosphoric acid produced from the Moroccan sedimentary phosphate rocks. The phosphoric acid is produced at different P2O5 concentrations, ranging from 18% P2O5 up to 54% P2O5. The rheograms experimentally elaborated under a range of temperature from 22°C to 80°C, allowed us to determine the rheological behaviours and the appropriate models for these acids. The recorded results indicate that the Herschel–Bulkley model fits all the acids perfectly under the different conditions, with regression coefficient R 2 greater than 99.3% and mean absolute error of less than 0.142. Furthermore, we managed to develop a mathematical model that describes the apparent viscosity of this acid in terms of P2O5 concentration and temperature. The model obtained presents a regression coefficient of 79.26% and a mean absolute error of 4.111.

Leaching of rare earth elements from phosphogypsum

High amounts of phosphogypsum (PG) are generated in the production of phosphoric acid. Previous literature demonstrates that obtaining rare earth elements (REE) from PG is a promising alternative to managing this waste. However, the reported leaching efficiencies are low in most cases, or drastic leaching conditions are required. Therefore, this work aimed to study the leaching conditions of REE from PG to obtain high leaching efficiency values. Initially, a 24 factorial experimental design investigated the factors that affect the conventional acid leaching of REE from PG (leaching acid (citric and sulfuric acid), solid/liquid ratio, acid concentration, and temperature). Better leaching efficiency values of the sum of all REE (62.0% and 89.7% for citric and sulfuric acid, respectively) were obtained using an acid concentration of 3 mol L−1, solid/liquid ratio of 1/20 g mL−1, and temperature of 80 °C. Subsequently, the experiments optimization, performed through a central composite rotational design, indicated that the maximum leaching efficiency was achieved using a sulfuric acid concentration of 2.9 mol L−1, solid/liquid ratio of 1.7/20 g mL−1, and 55 °C. Under these conditions, the leaching efficiency of the sum of all REE was 90.0%. Leaching kinetics results showed that the equilibrium was reached in about 20 min for most REE. The mechanism investigation suggested that surface chemical reaction and diffusion through the boundary layer controlled the leaching.

Wet Process Phosphoric Acid Purification Using Functionalized Organic Nanofiltration Membrane

The utilization of phosphoric acid in various sectors, e.g., food industry, is controlled by the authorized concentration limit of impurities. However, industrial phosphoric acid is contaminated with undesirable impurities (such as F, Al, Fe, Mg, etc.). Herein, this study aimed to evaluate the efficiency of the membrane purification process of pretreated industrial phosphoric acid using a premodified nanofiltration membrane. We demonstrated that the prior pretreatment steps for industrial phosphoric acid allowed the elimination of sulfate, fluorine and arsenic. Further purification of the obtained pretreated phosphoric acid using membrane cells reduced the concentrations of Cd, Al, Fe and rare earth elements by 94.81, 99.30, 99.63 and 96.67%, respectively. The membrane is functionalized by a deposit of a high molecular weight polycationic polymer of polyethyleneimines in order to produce a highly charged membrane surface to enhance the separation efficiency, selectivity and stability of the membrane. We found that the purification process relies on electrostatic repulsion between the functionalized membrane and highly charged ions, and the reduction rate of metals is a cation charge-dependent parameter. The laboratory and industrial pilot scale results showed that this process allows the production of food-grade phosphoric acid.

Removal of feldspar from phosphate ore using Gemini quaternary ammonium salt as a novel collector

Feldspar is a typical sesquioxide which is associated with phosphate ore. It can greatly prevent the formation of calcium sulfate crystals during the wet process of phosphoric acid production, resulting in the loss of P2O5, and therefore lowering the phosphoric acid recovery. To achieve the selective separation of feldspar from phosphate ore, we first tried using a new Gemini quaternary ammonium salt as the collector in conjunction with a reverse flotation approach. The flotation tests of single minerals and artificially mixed minerals were employed to investigate the collecting ability and selectivity of the collector, the adsorption mechanism was also evaluated by means of zeta potential measurements and molecular dynamic calculations. The flotation results demonstrate that the collector showed a strong harvesting effect and selectivity on feldspar rather than fluorapatite. When the Gemini concentration was set at 7.5 × 10−6 mol/L, the P2O5 grade could reach 31.69% with a corresponding recovery of 77.57%, indicating that Gemini collector could suitably be used as a potential chemical to achieve the effective removal of feldspar from phosphate ore. The results obtained from zeta potential measurements and molecular dynamics simulations indicate that the adsorption of Gemini collector on feldspar was more pronounced compared to that on fluorapatite surface and the interaction between Gemini and both minerals was mainly ascribed to electrostatic interaction. This work aims to provide a reference for using Gemini as collector combined with reverse flotation approach to achieve the effective removal of sesquioxide from phosphate ore and further enhance the quality of phosphate fertilizers.

Better filterability and reduced radioactivity of phosphogypsum during phosphoric acid production in Morocco using a fly ash waste and pure silica additive

Reactive silica additives, such as clays, can increase the filterability of phosphogypsum (PG) during wet phosphoric acid production from phosphate rock (PR). In this study, the effect of adding inexpensive fly ash waste (34 kg per t PR) together with lower quantities of pure silica (8.5 kg per t PR) on the radioactivity of PG was investigated. The addition of fly ash waste/pure silica reduced the radiological activity of the PG by roughly 30%. The reduction was attributed to decreased activities from 238U (60% reduction) and 226Ra (30% reduction) in PG. Besides, P2O5 losses were slightly decreased.

Advanced oxidation processes for wet-process phosphoric acid: Enhanced phosphorus recovery and removal of organic matters

Green and efficient phosphorus leaching from phosphate rock (PR) is the key to producing high-quality products and reducing energy consumption. Organic matters in the PR affect the efficiency of wet-process phosphoric acid production. In this study, advanced oxidation processes (AOPs) were employed to remove organic matters, thereby intensifying the acidolysis reaction of the PR. The characteristics, effects of reaction conditions on the leaching efficiency, and leaching reaction were systematically studied. Under the optimal reaction conditions with the H2O2 concentration of 0.04 mL/mL, reaction temperature of 70 °C, reaction time of 120 min, and particle size of −150 μm, a high leaching efficiency of 88.4% was achieved in the O3-H2O2 reaction (OHR) case. In addition, the total organic carbon content in the leach liquor is 12.2 mg/L, which is significantly decreased by 79.9%. This demonstrated the advantages of AOP systems in strengthening the efficient leaching of phosphorus as well as beneficial environmental impact.

Complex processing of phosphogypsum

The raw material base for many branches of the chemical industry is depleting; the issue of involving in the production of both raw materials with a low content of useful components and industrial waste becomes more and more urgent. Waste from production falls as a dead load on the cost of production of enterprises and often gives rise to a number of difficult-to-solve problems. This also applies to phosphogypsum ,i. e. a large-tonnage waste from the production of phosphoric acid by the sulfuric acid method. Phosphogypsum contains elements such as Ca, Mg, F, P, Si, Sr and rare earth elements. Secondary waste generated in this case is of limited demand and is practically not used. The complex composition of phosphogypsum as a raw material for the chemical industry should be considered as an opportunity to reduce mining, provided that the valuable components that make up its composition are maximally extracted from it into marketable products. The problem can be successfully solved using the technology of complex processing. Complex processing can be conditionally divided into three stages: obtaining ammonium sulfate or sodium sulfate; concentrate of rare earth elements; calcium silicate or calcium carbonate. Phosphogypsum processing is aimed at solving environmental problems that exist during its storage in dumps at phosphate fertilizer enterprises; at the same time, the negative impact of phosphogypsum components on the environment is reduced.

Preparation of belite–sulphoaluminate cement using phosphate rock acid-insoluble residue

In the phosphorous–sulfur two-step process involved in the clean production of phosphoric acid, the acidolysis of phosphate rock yields a solid filter phosphate rock acid-insoluble residue (PAIR). Herein, belite–sulfoaluminate cement is prepared using the PAIR as the main silica source to promote the residue resource utilization. The PAIR has practical feasibility for belite–sulfoaluminate cement preparation. Preparation conditions comprising the basicity coefficient of the raw meal of 1.187, clinker calcination temperature of 1200 °C, and the holding time for clinker calcination of 1.0 h are employed. Under these conditions, calcium sulfoaluminate and dicalcium silicate, the main mineral phases of the clinker, are fully formed, exhibiting contents close to the theoretical design value. The high amounts of fluorine and phosphorus in the PAIR reduce the clinker sintering temperature by 50 °C–150 °C and activate the clinker mineral phase. The maximum ɑ′ dicalcium silicate content in the clinker is 20.233%. The hydration and mechanical properties of the prepared belite–sulfoaluminate cement are better than those of commercial 42.5 grade cement. Moreover, its 28-day compressive strength can reach 64 MPa.

Comparative evaluation of methods for determination of the rare earth elements content in phosphate raw materials

The increase in the rate of extraction and use of rare earth elements (REE) necessitates the study of their environmental and industrial safety. Despite the relatively low content of REEs in phosphate ores (less than 1.5% (wt.)), significant volumes of production of phosphoric acid and mineral fertilizers based on it require environmental monitoring of REEs both in the soil located in the immediate vicinity of phosphogypsum dumps and in the phosphate fertilizers themselves, which are the main source of REEs in it, paying special attention to the irreplaceable soils of greenhouse farms. Inductively coupled plasma mass spectrometry (ICP &ndash; MS) occupies the leading position today among the variety of direct methods for the quantitative determination of REEs. However, for a number of domestic producers of phosphate fertilizers, the ICP &ndash; MS method is still too complicated and expensive. As an affordable alternative, we can mention the spectrophotometric method (SPM), based on the formation of a colored complex of rare-earth elements with the analytical reagent Arsenazo III. On the example of a sample of phosphorite from the Polpinsky deposit, a comparative assessment of the possibility of quantitative determination of REEs in phosphate raw materials by the ICP &ndash; MS method is presented as the most promising, as well as the SPM as the most accessible. It is shown that the sensitivity of the spectrophotometric method is sufficient for the reliable determination of the amount of REEs in the phosphate raw material. The reasons for significant errors in determination of the amount of REEs in phosphate raw materials by the photometric method and possible ways to reduce them to values comparable with the error of the method are considered.