Wet Phosphoric Acid Research Articles

Enhancing wet phosphoric acid production efficiency with vanadium catalyst waste derived silica

Filtration of phosphogypsum (PG) is an important step in the production of wet phosphoric acid (WPA). In recent years, the phosphate rocks used for WPA production in Morocco started showing deficiencies in terms of their reactive silica content that affects PG crystallization and as such decreases PG filtration efficiency and subsequently the overall efficiency of the WPA production. In this work reactive silica waste from spent vanadium catalysts, used in the production of sulfuric acid for WPA production, was added to the digestion process in an attempt to increase WPA production efficiencies. The laboratory work presented here shows that the added silica improved the quality of the produced dihydrate WPA by 6 %. Besides, the chemical yield of the reaction was improved by 5 % as a result of the shape-change of the PG crystals that allowed for better filtration. The results of this work are promising and we strongly recommend testing this approach on larger pilot- and ultimately industrial scale.

Desilication and purification of phosphogypsum waste by flotation using a photosensitive collector

Phosphogypsum (PG) is the main by-product of wet phosphoric acid production and has seriously polluted the environment. In this study, PG was purified by reverse flotation using a photosensitive azobenzene surfactant (PASF). After reverse flotation, the content of gypsum in PG increased from 89.16 % to 93.32 %, the whiteness of PG increased from 25.62 % to 60.9 %, and the content of quartz decreased from 4.87 % to 2.12 %. The Zeta potential of quartz and gypsum became positive after being treated with PASF, indicating that PASF enhanced the floatability of quartz and gypsum. The results of FTIR and XPS indicated that there were both electrostatic attraction and hydrogen bonding between PASF and quartz. Density functional theory (DFT) calculations indicated that the adsorption of PASF on the quartz surface was more stable than on the gypsum surface. Upon exposure to UV irradiation, the molecular structure of PASF was transformed from trans to cis. Meanwhile, the adsorption amount of PASF on the quartz surface was decreased and the rigidity of the corresponding adsorbed layer was increased. This work provides a method to purify PG waste, which is important for the comprehensive utilization of PG.

Removal of magnesium and aluminum from wet phosphoric acid by ralstonite precipitation: Thermodynamic and performance analysis, mechanistic studies and precipitate characterization

The purification of wet-process phosphoric acid has always posed a challenge for both academic and industrial researchers. In order to address this issue, a treatment unit was developed to mitigate magnesium and aluminum impurities from industrial semi-aqueous wet process phosphoric acid (SWPPA) (39.4 wt% P2O5) through ralstonite precipitation using Na+/F− as the precipitator (F− provided by HF). Thermodynamic analysis, DFT calculation and separation experiments results were used to investigate the impact of sodium sources properties on impurities removal rates and H3PO4 yield. Additionally, the effects of reaction temperature, reaction time, precipitating agent dosage, and aging time on precipitation efficiency were also examined. The results show that the ability of sodium source to ionize Na+ and react with H3PO4 and HF plays a crucial role in determining the impurity removal performance of magnesium and aluminum. The precipitants NaCl and Na2CO3 exhibit the highest removal rates for magnesium and aluminum, which is attributed to the easy ionization of Na+ ions. In comparison to Na2CO3, the higher H3PO4 yield with NaCl as precipitator can be achieved due to its lower nucleation rate and higher crystal growth rate in the phosphoric acid system. NaCl and HF as precipitants effectively reduces the concentrations of magnesium and aluminum in the untreated SWPPA solution from 23.47 g MgO/kg P2O5 to 3.29 g MgO/kg P2O5, 48.98 g Al2O3/kg P2O5 to 15.54 g Al2O3/kg P2O5. The removal rates for magnesium and aluminum are found to be 85.98% and 68.27%, respectively, with minimal residue of Na+/F−.

The ultramicropore biochar derived from waste distiller’s grains for wet-process phosphoric acid purification: Removal performance and mechanisms of Cr(VI)

Solid waste and heavy metal pollution are long-term and challenging subjects in the field of environmental engineering. In this study, we propose a sustainable approach to “treating waste with waste” by utilizing the ultramicropore biochar derived from solid waste distiller’s grains as a means to remove Cr(VI) from simulated wastewater and wet phosphoric acid. The biochar prepared in this research exhibit extremely high specific surface areas (up to 2973 m2/g) and a well-developed pore structure, resulting in a maximum Cr(VI) adsorption capacity of 426.0 mg/g and over 99% removal efficiency of Cr(VI). Furthermore, the adsorbent can be reused for up to eight cycles without significant reduction in its Cr(VI) adsorption performance. Mechanistic investigations suggest that the exceptional Cr(VI) adsorption capacity can be attributed to the synergistic effect of electrostatic interaction and reduction adsorption. This study offers an alternative approach for the resource utilization of solid waste distiller’s grains, and the prepared biochar holds promise for the removal of Cr(VI) from wastewater and wet-process phosphoric acid.

Removal of Organic Matter from Tunisian Industrial Phosphoric Acid by Adsorption onto Purified Natural Illite/Kaolinite Clay: Kinetics, Isothermal and Thermodynamic Studies.

This work aims to use a green, economical and efficient adsorbent to remove organic matter from Tunisian industrial wet phosphoric acid (WPA: 52% P2O5). For this purpose, a natural and abundant clay is extracted from the Douiret, Tataouine deposit in southern Tunisia. This clay is being tested for the first time as an adsorbent in WPA medium. The raw clay and purified clay are analysed using standard analytical techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, and BET methods. The results show that the raw clay is a mixture of illite and kaolinite, with other mineral impurities, mainly quartz. Organic matter adsorption tests show that the purified clay exhibits greater effectiveness than raw clay. The parametric study with purified clay indicates that temperature, contact time, and clay dosage strongly influence organic matter adsorption. The highest adsorption occurs at 60 °C after 50 min, reaching 56% with 8 g of purified clay per kg of WPA. Among several recognised models, the pseudo-second-order kinetic model and the Sips isotherm model are the most suitable for modelling the experimental data. This study suggests that Douiret clay can be considered an effective, inexpensive and environmentally friendly adsorbent for eliminating organic matter in industrial phosphoric acid.

Efficient extraction of impurities from phosphogypsum during crystal regulation of α‐hemihydrate gypsum

AbstractPhosphogypsum (PG) is a solid waste generated during the “wet phosphoric acid process.” The phosphorus (P) impurities and low‐value‐added recycling products seriously constrain PG re‐utilization, which results in its massive accumulation and thus occupies large land areas and poses a severe pollution threat to the environment. In this study, by regulating gypsum crystal and P species in CaCl2–HCl solutions under mild conditions, efficient removal of P impurities (leaching efficiency of 97.78%) and synchronous preparation of high‐strength α‐CaSO4·0.5H2O (α‐HH) (compressive strength of 35.2 MPa) from PG were achieved during the phase transition from CaSO4·2H2O (DH) to α‐HH, which was a reaction of DH dissolution, followed by α‐HH crystallization. The co‐crystalline P was fully released during the dissolution process, which was necessary to efficiently eliminate P impurities. HCl dissolved the released P and transformed them into the protonated specie (H3PO4) with less similarity to SO42−, which prevented the recombination of the released P with gypsum during the crystallization process. Furthermore, α‐HH morphology and size were controlled by seeding in the mixed solutions. The formation of regular large α‐HH crystals with a low‐specific surface area significantly weakened the surface adsorption of P in solutions and further increased the P leaching efficiency. More importantly, the large stumpy α‐HH was identified as high‐strength gypsum with high added value. This work would provide innovative guidance to efficiently remove impurities from gypsum and pioneer a cost‐effective approach for clean and high‐value utilization of industrial gypsum residues.

Process of preparing chloride-free KNS compound fertilizers from phosphogypsum waste using a quaternary phase diagram

Phosphogypsum (PG), commonly known as calcium sulfate, is a waste by-product generated during the production of phosphoric acid by the wet phosphoric acid process (WPA). It is well known that every year the phosphate industries produce a large quantity of PG around the world (i.e., Currently, global production of this waste is estimated at 300 Mt/ year), but the valorization processes of this waste are limited and low valuable. In this study, we investigated the recycling of PG by-product, which can be considered very promising sources of sulfate ions (SO42-) for the manufacturing of chloride-free KNS compound fertilizer based on potassium-ammonium sulfate ([K1−x(NH4)x]2SO4). The primary objective of this study was to develop a methodology for [K1−x(NH4)x]2SO4 synthesis and its separation process using the quaternary phase diagram K+, NH4+ / Cl-, SO42- - H2O at 25 °C. The experiment results show that it is possible to recover relatively pure (NH4)2SO4 from PG to re‐synthesize in presence of KCl the [K1−x(NH4)x]2SO4 phase, whose high quality and purity were confirmed by the combined use of several analytical and characterization techniques such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and gamma spectrometry analysis. The thermal decomposition was supplemented by Thermo-Gravimetric Analysis (TGA) coupled with Differential Thermal Analysis (DTA). The main findings of this study may assist in developing methods for valorizing PG waste by converting it into valuable fertilizer products, which are particularly suitable for cultivating chloride-sensitive crops. Thus, total or partial substitution of non-renewable resources by PG not only helps to solve the environmental pollution caused by this waste, but also reduces production costs and improves farm economics.

Uranium supply potential from imported phosphate rocks for the Philippine nuclear power program

The Philippines is planning to rehabilitate its mothballed Bataan Nuclear Power Plant (BNPP) to provide affordable electricity and meet carbon emission goals. Despite not having domestic uranium resources, the Philippines import considerable amounts of phosphate rock for mineral fertilizer production that is known to contain between 50-200 mg uranium per kg ore. Recovering the uranium from phosphate rock during wet-phosphoric acid (WPA) production, the process used in the Philippines, is a mature technology that was used at fertilizer plants in Florida in the 1980s and 1990s before decreasing uranium prices made it unprofitable. Uranium prices are bound to rise again, and this work estimates the amount of uranium that could be recovered during WPA production in the Philippines. We estimate that between 14.4-25.6 t natural uranium could have theoretically been recovered annually in 2020, 2021 and 2022. This amount is equivalent to approximately 12-21% of the projected annual uranium requirements of the BNPP. Phosphate rock imports into the Philippines are still below pre-Typhoon Haiyan levels and when the industry recovers it is likely that more than one-fourth of the uranium requirements of the BNPP could be met with unconventional uranium recovered from imported phosphate rocks.

CATALYSTS AND ADSORBENTS FOR CONVERSION OF NATURAL GAS, FERTILIZERS PRODUCTION, PURIFICATION OF TECHNOLOGICAL LIQUIDS

The work is devoted to investigation of catalysts and adsorbents used in the production of ammonia, methanol, and formaldehyde, hydrogenation of various organic compounds, defluorination of wet phosphoric acid, adsorptive wastewater treatment, and inhibition of combustion chain reactions. Main approaches for the synthesis of adsorption-catalytic systems, governing the composition, structural and textural properties and providing specific functionality, were studied. Those included mechanochemical synthesis and activation, surface modification, precipitation, impregnation, etc. For citation: Kunin A.V., Ilyin A.A., Morozov L.N., Smirnov N.N., Nikiforova T.E., Prozorov D.A., Rumyantsev R.N., Afineevskiy A.V., Borisova O.A., Grishin I.S., Veres K.A., Kurnikova A.A., Gabrin V.A., Gordina N.E. Catalysts and adsorbents for conversion of natural gas, fertilizers production, purification of technological liquids. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 132-150. DOI: 10.6060/ivkkt.20236607. 6849j.

A novel and complete process for iodine extraction and recovery from industrial wet-process phosphoric acid based on chemical oxidation and solvent extraction

Due to their copious availability and broad applicability, iodine recovery from numerous sources, such as byproducts of various industrial processes, has attracted attention. To meet growing market demand for iodine as well as to accomplish long-term management of iodine resources, phosphate rocks and their derivatives were discovered as a possible source of iodine. As phosphoric acid is produced in significant quantities each year more than 20 million tons the extraction of iodine, a byproduct of the wet processing of phosphoric acid, is crucial. This research aims to develop a pre-oxidation and solvent extraction-based method for recovering high purity iodine from wet phosphoric acid (SX). For this purpose, the effects of operating variables, such as: time, acidity, dose of the oxidant, temperature, volume ratio, and the concentration of stripping solution have been studied. Using 30% H2O2 as an oxidant, all the iodides ions present in wet phosphoric acid was converted into elemental iodine. The iodine was then extracted and stripped quantitatively using pure kerosene and 0.02 M sodium sulfite at ratios (O:A) of 1:2 and 1:1, respectively. The resulting iodine precipitate was subjected to several analyses, including iodometric titration, XRD, and ICP-OES, which confirmed its purity to be 99.9%. Finally, a flowchart process for both recovering and reducing the loss of iodine from wet phosphoric acid was developed without interfering with the normal fertilizer production route.

Study on the Phosphogypsum Proportion in Foamed Concrete Based on Concrete Strength and Carbon Emission

The production of concrete will produce a lot of carbon dioxide and pollute the environment. Phosphogypsum is a solid waste generated during wet phosphoric acid treatment, and the use of phosphogypsum blending instead of cement in concrete production can effectively reduce carbon dioxide emissions. Then, experiments were conducted for six concrete groups with different phosphogypsum content as 0%~50% to test the strength in 3 days, 7 days, and 28 days. The results show that as the curing day rise, the compressive strength of concrete increases, meanwhile, with the increment of phosphogypsum content, the 28-day strength decreases significantly. The analysis for the consideration of the balance in carbon emission and the strength evolved, and results could be concluded that although the decrement of 28-day strength as well as the carbon dioxide emissions with the increasing phosphogypsum content in concrete, different trends were found. As the strength and emissions vary, a suggested range of content for phosphogypsum in concrete can be found. Based on these results, the proportion of phosphogypsum in concrete is proposed to achieve the purpose of energy saving and emission reduction and improve the utilization rate of phosphogypsum.

Surface modification of anhydrous phosphogypsum and its application in isotactic polypropylene

Phosphogypsum (PG) is a by-product of the wet phosphoric acid process, and anhydrous phosphogypsum (APG) prepared by PG calcination and ball milling pretreatment can be useful to prepare polypropylene composites by melt blending to yield polymer materials with improved properties. In this work, the hydrophobic effect of stearic acid (SA) modified APG was investigated by various analytical techniques. To this end, the modified APG was used as a filler for isotactic polypropylene (PP) blending to yield PP/APG composites and study the influence of APG particle size and added amount on the mechanical properties of PP/APG composites. The results showed SA coated on APG surface by chemical adsorption to form a hydrophobic layer. The water contact angle increased from 8.49° to 112.49° before to after modification, respectively. The mechanical properties of PP/APG composites were affected by the particle size and content of APG. Smaller particle size of APG led to better mechanical properties of PP/APG composites. At particle size d50 of APG filler of 2.83 μm and content of 5 wt%, characteristics like the tensile strength, flexural strength, impact strength, and tensile modulus of PP/APG composites reached 37.28 MPa, 47.71 MPa, 6.18 KJ/m2, and 422.3 MPa, respectively. Compared to pure PP, these values increased by 4.66%, 5.4%, 27.68%, and 18.28%, respectively. Smaller particle size of APG was also found more conducive to the increase in APG content within PP/APG composites, as well as reduced production cost of composites. APG prepared from PG after treatment is useful as a filler for PP and other polymer materials, promising for PG resource utilization.

Identification and Quantification of the Organic Matter in the Fouling Industrial of Wet Phosphoric Acid Process

The organic matter of rock phosphate has been the subject of numerous studies. The valuation and resolu-tion of some problems, such as fouling, encountered in the industrial production of phosphoric acid are of great interest, and enable better production yields of phosphoric acid. The solid deposits formed in the production of wet process phosphoric acid were characterized and revealed the malladrite, gypsum, trace metals, and the presence of organic matter. The identification of the organic matter was carried out in the fouling samples using FT-IR and Raman spectroscopies. The quantitative determination of the total organic matter content of the fouling samples was performed using the Walkley-Black and calcination methods. The knowledge of the organic matter in the fouling layers allows a better understanding of phenomena in processes.

Structural and Distribution of Impurities in the Fouling in Wet-Process Phosphoric Acid at T = 80°C

In this investigation, the mineral deposits formed in the digestion step in wet phosphoric acid production were studied. The mineralogical characterization of the fouling precipitates obtained at the temperature 80°C from the digestion step in 16-monthly production cycle was carried out. Observing successive layers, based on their colors, allowed us to distinguish fouling layers. Detailed structural aspects, and subsequently, chemical and physical properties of the fouling were determined using complementary analytical and characterization techniques. Particle size fractionation was then used to gain each fouling layer sample homogenized on the micro-scale (63μm). The major elements in the fouling were determined to be silica (Si₂O) and sodium (Na). Some chemical elements of major impurities, as well as traces, K, Al, Mg, Fe, Cu, and Zn, were detected using XRF which cannot appear in their proper solid phases. The obtained solid phases in different fouling layers are principally composed of the malladrite and gypsum minerals. The distribution of impurities into the present structures was investigated. Indeed, the mesh parameters of malladrite in the fouling layers were calculated and compared with those of the pure phase, and a good concordance is obtained. The FT-IR spectra confirm the presence of mallardite and gypsum phases and reveal a supplementary band that has been assigned to C-O vibrations in acids, esters, or ethers. The appearance of this band indicates the possible presence of organic matter within the fouling layer.

Optimization of microwave assisted synthesis of activated carbon from biomass waste for sustainable industrial crude wet-phosphoric acid purification

Crude phosphoric acid, generated during industrial wet production, requires careful treatment by different processes to make it acceptable for various agro-industrial applications. The purification of crude phosphoric acid is still challenging and costly at a large scale because of the presence of various organic and inorganic pollutants. The adsorption technique for the purification of crude phosphoric acid suffers from the low sorption rate due to its complexity in terms of chemical composition and low pH. To enhance the sorption selectivity, the texture and surface chemistry of activated carbon should be well designed via the optimization of synthesis conditions. The present work aims to valorize local biomass waste (palm petiole, PP) into highly mesoporous adsorptive activated carbon (ACPP) for the removal of the organic matter (OM) from crude industrial phosphoric acid (26% P2O5). The microwave-assisted synthesis of ACPP was optimized using full factorial design (FFD) and analysis of variance (ANOVA). Experimental factors that govern the removal of OM from phosphoric acid using ACPP were investigated to maximize the purification rate. Even though the yield of OM in phosphoric acid is high, ACPP removes about 81.5% of OM. Several parameters were studied to optimize and understand the adsorption behavior of OM on the surface of ACPP. The adsorption process undergoes pseudo-second-order kinetic, and the adsorption isotherm follows the Sips model. Overall, this research shows that the carbonization of biomass assisted by microwave and the use of H3PO4 as activation agent produces a highly adsorptive activated carbon with high affinity towards removing OM from crude phosphoric acid. Optimizing biomass waste carbonization factors by facile and sustainable routes would benefit industries to produce pure phosphoric acid at a low cost and eco-friendly route.

Quality of Phosphate Rocks from Various Deposits Used in Wet Phosphoric Acid and P-Fertilizer Production.

Phosphate rocks (PRs) play a crucial role in ensuring the availability of phosphorous for the world's food needs. PRs are used to manufacture phosphoric acid in the wet process as well as P-fertilizers. The chemical and mineralogical compositions of PRs from Djebel Onk (Algeria), Khneifiss (Syria), Negev (Israel), Bou Craa (Morocco), and Khouribga (Morocco) are discussed in this study. PRs were characterized by inductively coupled plasma optical emission spectrometry (ICP-OES), cold vapor atomic absorption spectrometry (CVAAS), ion chromatography (IC), and X-ray diffraction (XRD), as well as gravimetric and potentiometric methods. All PRs were mainly composed of CaO, P2O5, SiO2, F, SO3, Na2O, MgO, Al2O3, Fe2O3, SrO, and K2O at the level of wt.%. The P2O5 content accounted for 28.7-31.2%, which indicates that these are beneficial rocks to a marketable product. The degree of PR purity expressed by the minor elements ratio index (MER index) varied from 2.46% to 10.4%, and the CaO/P2O5 weight ratio from 1.6 to 1.9. In addition, the occurrence of trace elements such as As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Ti, V, U, and Zn, as well as Cr(VI) and Cl ions at the level of mg∙kg-1 was found. Since PRs will be used to produce P-fertilizers, their composition was compared with the regulatory parameters set up by EU Regulation 2019/1009 related to the heavy metals (As, Cd, Pb, Ni, Hg, Cu, Zn) and Cr(VI) contents in inorganic fertilizers. The heavy metals and Cr(VI) content in all PRs did not exceed the limit values. XRD analysis revealed that fluorapatite, hydroxyapatite, carbonate fluorapatite, and carbonate hydroxyapatite were the dominant minerals. The accuracy and precision of the used methods were evaluated by analysis of standard reference materials (SRM) for Western Phosphate Rock (NIST 694). The recovery was 85.3% for U and 109% for K2O, and the RSD ranged from 0.67% to 12.8%.

Experimental investigation of iron removal from wet phosphoric acid through chemical precipitation process

In the present work, the combination of experimental investigation and statistical analysis has been used for the first time to study iron precipitation from wet-process phosphoric acid. Firstly, eight types of additives including different carbonate and hydroxide salts were studied in the chemical precipitation reaction in order to decrease the iron content in wet-process phosphoric acid. From different studied reagents, calcium carbonate and calcium hydroxide showed the best to remove ferric ions from crude wet-phosphoric acid. Under the optimum conditions, about 80% and 83% of the iron can be removed at 70 ℃ after the addition of calcium carbonate and calcium hydroxide, respectively. The maximum P2O5 losses from crude phosphoric acid was less than 4% after the addition of calcium hydroxide. Based on the Arrhenius behavior, the activation energy of iron precipitation was calculated about 47.43 and 51.55 kJ/mol for calcium carbonate and calcium hydroxide addition, respectively. The iron state studies showed that the pretreatment process was unnecessary to reduce iron state from ferric to ferrous form before precipitation. Furthermore, the kinetics parameters showed that the iron precipitation process was an endothermic reaction. The XRD analysis of the precipitates produced confirmed the formation of Fe(OH)3, α-Fe2O3, α-FeOOH and FeCO3 through the reaction of iron with carbonate and hydroxide ions. Possible pathways of iron precipitation were proposed. Both calcium carbonate and calcium hydroxide showed good efficiency to remove iron from wet-process phosphoric acid accompanied by moderate P2O5 losses. The Taguchi technique was applied to optimize the parameters using signal-to-noise ratio analysis as well as ANOVA. The analysis showed a greater susceptibility of the response against changes in the value of calcium carbonate, more than calcium hydroxide.

Kaolinite/thiourea-formaldehyde composite for efficient U(VI) sorption from commercial phosphoric acid

Abstract Uranium removal from wet phosphoric acid is a vital process for food and environmental security. The incorporation of thiourea-formaldehyde into the kaolinite networks was performed to obtain an effective and acid-resistant sorbent. The prepared composite was applied for U(VI) uptake from crude phosphoric acid. X-ray diffraction, EDX, scanning electron microscopy, and Fourier transform infrared analyses were carried out to explore the properties of the yield composite. The sorption characteristics, i.e., capacity, kinetic, isotherm, and thermodynamic were investigated. The anticipated data declare that the reaction is fast whereas 60 min is sufficient to reach the equilibrium state. The experimental results obeyed to Pseudo second-order kinetic model and Langmuir isotherm model. The maximum sorption capacity was about 5.8 mg g−1. Thermodynamic parameters displayed that the sorption process is endothermic, feasible, and spontaneous. The displayed results demonstrate that the prepared composite could be used as the proper material for producing eco-friendly fertilizers.

Purification of industrial wet phosphoric acid solution by sulfide precipitation in batch and continuous modes: Performance analysis, kinetic modeling, and precipitate characterization

The purification of wet-process phosphoric acid has always been a challenge for both academic and industrial researchers. A treatment unit was developed to mitigate metallic impurities, such as cadmium, from industrial dilute wet phosphoric acid solution (25% P2O5) by NaHS precipitation in batch and continuous modes. The effects of operating parameters on the purification performance were evaluated: namely Sulfur/Cd2+ molar ratio, the presence of other metallic ions besides Cd2+, temperature, and hydraulic residence time. In the batch mode, equilibrium was attained in less than 20 min; augmenting Sulfur/Cd2+ molar ratio increased the CdS precipitation effectiveness up to 86%, but temperature increment had an adverse effect. In the continuous mode, a hydraulic residence time of 40 min was necessary to reach the same yield as in the batch mode at 25 °C. Sulfidation was found to eliminate simultaneously other metallic impurities (especially Cu and As) originally present in the wet-produced phosphoric acid. Finally, NaHS precipitation was able to reduce the concentration of cadmium from 65.95 mg Cd/kg P2O5 to 11.15 mg Cd/kg P2O5 from untreated industrial WPA solution (25% P2O5) at 25 °C, which outperforms most of the published data based on alternative treatment processes.

Highly selective complexation of cadmium from wet phosphoric acid by organic coordination ligands

Recently, the application of organic coordination ligands for the cadmium removal from wet phosphoric acid (WPA) has shown a great interest, and a certain number of commercially available ligands have shown some affinity and selectivity for cadmium. This technic consists in making complexes between cadmium and ligands. It is easy to integrate industrially and does not require significant investment and maintenance overhead; the cost is driven by the organic ligand stability, efficiency and price. However, the challenge still the high cost of ligand and its insufficient world production capacity in comparison to the increasingly demand. The present research article aims to experiment new organic ligands potentially proved in various media for the cadmium removal. The cadmium removal tests from WPA were carried out under the industrial conditions of 25 % (w/w) P2O5, 14 ppm Cd, and 80 °C. A number of 21 organic ligands were carefully selected based on their potential removal of cadmium. The tests were separately performed under the stoichiometric conditions corresponding to a molar ratio R (nLigand/ncd) of 2, and the excess conditions corresponding to a molar ratio R (nLigand/ncd) of 10. Distinctly, the results relatively to R equaling 10 showed significant increase in cadmium removal specifically to DIBDPi (Diisobutyl dithiophosphinate), DEDTP (Diethyl dithiophosphate), ZDDP (Zinc dialkyl dithiophosphinate), TBAI (Tetrabutyl ammonium iodide), Na2CS3 (Sodium trithiocarbonate), and Aliquat 366 (Methyltrioctyl ammonium chloride), with an efficiency of 86 %, 71 %, 68 %, 29 %, 24 %, and 21 %, respectively. The other ligands still showed no affinity for cadmium removal from WPA.