Production of pure phosphoric acid from El-Sebaeya low-grade phosphate ore

The extraction of phosphoric acid by tributyl phosphate (TBP) in kerosene from hydrochloric acid leach liquor of El-Sebaeya low-grade phosphate ore was carried out. The influence of various factors affecting the leaching process such as particle size, reaction time, acid concentration, liquid/solid mass ratio, reaction temperature and stirring speed were thoroughly studied to estimate the favor phosphate ore dissolution in relation to impurity. Thereafter, the effects controlling the extraction step, including shaking time, solvent concentration, aqueous/organic phase ratio, and reaction temperature, have been studied in terms of the maximum P₂O₅ extraction efficiency and the minimum impurities extraction efficiency. The obtained loaded organic solvent was subjected to the stripping stage using double-distilled water. The outlet stripping liquor was concentrated by evaporation up to 62% P₂O₅.     

The potential of Hazara phosphates for phosphoric acid manufacture

The phosphate reserves in Pakistan are small. The largest ore body (Lagarban area) of Hazara Administrative Division located in the North East of the country has 3.25 (measured) and 6.71 (inferred) million tons phosphates rock of silicious and dolomitic nature with 25.8% average P₂O₅ contents besides high impurities of R₂O₃ (3.3%) and MgO (up to 6%).The deposits are not beneficiable by dry and wet screening due to significant phosphate losses which take place. Phosphate flotation recoveries are also low. Heavy intensity magnetic separation removes iron after the removal of dust from classified fraction. Acid leaching is efficient for removing MgO (up to 84%) with low P₂O₅ losses. However, removal of iron and MgO by these methods is not considered feasible on economic grounds.Laboratories and pilot plant processing trials showed that phosphoric acid of 23–25% P₂O₅ can be manufactured from Lagarban rock. As most of the impurities of the rock Fe₂O₃, Al₂O₃, MgO and part of SiO₂ are washed down during processing the resulting product acid is of poor quality with high viscosity.Triplephosphates prepared from this acid are hygroscopic and have low P₂O₅ availability (86%).To overcome the problem of these objectionable impurities in the product acid, removal of these impurities during the processing of phosphoric acid is required, i.e. aggolomeration with gypsum crystals-Pembrook pocess, Occidental process.     

Modélisation du traitement de purification de l'acide phosphorique de voie humide par la méthylisobutylcétone

The present paper reports results for the purification of phosphoric acid by liquid—liquid extraction with methylisobutylketone. The simultaneous effect of some operating parameters, namely concentration of the feed acid, massic ratio of solvent to feed, temperature and number of theoretical stages, on the performances of the extraction step has been examined using a factorial design 2⁴. The established models allowed us to forecast the experimental conditions required to obtain a given yield of P₂O₅ and/or a well‐defined quality of the stripped acid. The optimal conditions have been determined by using a desirability function.     

Evaluation of problematic indigenous phosphate deposits for phosphoric acid manufacture

To examine the possible utilization of indigenous phosphate reserves, bench scale studies were under-taken to assess their suitability for phosphoric acid manufacture.It was found out that in spite of few problems, the Silicious phosphate reserves of 2–3 million tons could be utilized for phosphoric acid manufacture, because low sulphuric acid consumption 2.52 ton acid/ton P₂O₅ and better P₂O₅ recovery yield (94.71) was achieved. The dolomitic phosphate reserves of 4–5 million tons (having 5–6% MgO) remained problematic, giving low P₂O₅ recovery yield (89.25) and higher sulphuric acid consumption 4.08 tons acid/ton P₂O₅.Product acid from the dolomitic reserves upon concentration became paste like at 36–38% P₂O₅ and therefore, these indigenous dolomitic phosphate reserves could not be utilized for the production of phosphoric acid.     

A PROCESS FOR DEFLUORINATION AND PURIFICATION OF WET PROCESS PHOSPHORIC ACIDS CONTAINING HIGH Al CONCENTRATIONS.

Abstract

A solvent extraction process is described for defluorination and desulfation of filter phosphoric acids with high Al content. The solvent used contain an amine and phosphoric acid as main constituents. The acid obtained is compatible with feed-grade requirements. It can be concentrated to 56–60% P₂O₅ by multiple effect evaporation, decreasing steam requirements by 50%. If an acid-base couple solvent is used in this process, part of the extracted phosphate can be recovered by back-wash with water in the form of highly purified phosphoric acid low in metals, fluorine and sulfate. The remainder of the acid along with the extracted sulfate is obtained as ammonium salt. The extracted F is converted into crystaline alkali fluorosilicate.     

Production of defluorinated dicalcium phosphate from phosphate rock concentrate

A new process to produce defluorinated dicalcium phosphate (DCP) using phosphate rock concentrate has been developed. This new process has as main characteristic the low concentration of P₂O₅ in the liquid phase. The process comprises three main steps: solubilization of the phosphate rock concentrate with sulfuric acid, defluorination of the phosphoric acid solution with potassium sulfate and neutralization of the phosphoric acid solution with calcium hydroxide. The P₂O₅ precipitated in the pH range between 2.00 and 5.00 consisted basically of anhydrous dicalcium phosphate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydration of calcium sulphate hemihydrate in the presence of phosphoric acid and calcium oxide: I. The kinetics of hydration

A study has been made of the effects of calcium oxide and phosphoric acid on the hydration of calcium sulphate hemihydrate. The reaction was studied with weight ratios of CaO/P₂O₅ increasing from 0 to 5, and with two levels of P₂O₅ concentrations, 0.1 and 0.2%. At the CaO/P₂O₅ weight ratio of 1–2, the velocity constant (k) of the reaction was reduced significantly; α₀, a measure of heterogeneous nucleation in the system increased 10 to 20-fold and the period of induction (θ) was increased substantially. The presence of phosphoric acid alone, and secondary calcium orthosphate hydrate (CaHPO₄.2H₂O), formed in situ, strongly retarded the hydration of calcium sulphate hemihydrate. The implications of these findings on the hydration of calcined by-product gypsum (phosphogypsum) are discussed.     

Analytik von Phosphorsäurepartialestern

Analytic of Phosphoric Acid Partial Esters Phosphoric acid partial esters are best synthesized by reaction of fatty alcohol with P₂O₅. The chosen mol ratio of fatty alcohol and P₂O₅ determines the amounts of mono-, di- and trialkylester, of oligomeric esters, of free fatty alcohol and of phosphoric acid. Several methods are used for the characterisation and determination of the individual components, the potentiometric titration, the ³¹P-nuclear magnetic resonance, the gel permeation chromatography, the ion chromatography and the supercritical fluid chromatography. The combination of all the results of the applied methods provides the key to the composition of the phosphoric acid ester. The results of the analysis are checked by a phosphorus calculation. This analytical procedure can be applied to phosphoric acid partial esters in the acid and salt form. The analysis of alkylethoxyphosphoric esters is done with the exclusion of the chromatographic methods.     

Some observations on the setting of calcium sulphate hemihydrate plaster in the presence of phosphoric acid and hydrated lime

The effects of additions of phosphoric acid and hydrated lime on the setting of calcium sulphate hemihydrate plasters have been examined. At two levels of P₂O₅ concentration (0.75 and 1.5 wt-% P₂O₅) it has been found that extreme retardation of the plaster setting process occurs with lime additions in the range, Ca(OH)₂/P₂O₅ (weight ratio) 0.5 to 1.5. The chemical nature of this effect has not been identified. Formation of either CaHPO₄. 2H₂O or hydroxyapatite in the paste is considered as deleterious to plaster hydration.     

Liquid–Liquid Extraction of Uranium from Phosphoric Acid by HDEHP–CYANEX-921 Mixture

The extraction of uranyl ions from different phosphoric acid media by CYANEX-921 (a commercial trioctyl phosphine oxide) mixed with di-2-ethylhexyl phosphoric acid diluted with odourless kerosene has been investigated. The effect of phosphoric acid, CYANEX-921 and HDEHP concentrations, as well as temperature on the extraction were studied. The extraction rate for UO₂²⁺ transfer from 5 M phosphoric acid to the organic phase containing a CYANEX-921–HDEHP mixture in a single drop column without external force was also studied. The mass transfer of uranium in the organic extractant single drop was investigated in terms of drop size, uranium concentration as well as other parameters. The extraction rate was found to be mainly dependent on uranium, HDEHP and phosphoric acid concentrations, and found to be mainly controlled by diffusion in the single drop. Further, it was found that CYANEX-921 can substitute TOPO to synergise the extraction of UO₂²⁺ by HDEHP. © 1997 SCI.     

Production of high-quality liquid fertilizers from wet-process acid via urea phosphate

A pilot-plant process is described that purifies wet-process phosphoric acid for the production of a high-quality urea-ammonium polyphosphate base solution. An intermediate product, crystalline urea phosphate, is produced from urea and merchant-grade (54% P₂O₅) wet-process phosphoric acid. The urea phosphate crystals contain only about 15 to 20% of the objectionable impurities (iron, aluminum, and magnesium) originally contained in the feed wet-process acid. The urea phosphate crystals are pyrolyzed, converting orthophosphate to polyphosphate with very little energy consumption. The resulting melt is dissolved and neutralized with ammonia to produce 14-29-0 liquid product of high polyphosphate content.     

EXTRACTION OF CADMIUM FBOM PHOSPHORIC ACID WITH DIORGANYLDITHIOPHOSPHINIC ACIDS. Part II: Rate of Extraction and Decomposition.

Liquid-liquid extraction of cadmium ions from 55-65 w% “black” phosphoric acid from a Nissan H process with diphenyldithio-phosphinic acid (DPP) or dicyclohexyldithiophosphinic acid (DCP)dissolved in an alkane(c₁₂or c₁₆) at 90°C was investigated.The rate of extraction of Cd from chemically pure phosphoric acid (55 w% H₃Po₄,90°C) is mainly determined by film diffusion of cadmium ions in the phosphoric acid phase to the interface. In the extraction from “black” acid, mass transfer in the organic phase or chemical reaction (ligand exchange) is probably the rate limiting step. An apparent mass-transfer coefficient (based on -5 [Cd] in the phosphoric acid phase) of about 1.6?10^?5 m/s was obtained for the extraction from “black” acid.

A fast decompositon of DPP was observed and in a batch experiment the Cd concentration was already more than 50% of the initial value after 6 hours. This phenomenon is probably caused by the formation of solid complexes with Cu, Cd and Zn, which are dispersed in the phosphoric acid phase and then oxidized. The decomposition of DCP proceeded much slower and after 30 hours the Cd concentration was still below 50% of the initial value. Cu formed a solid complex with DCP, whereas t.he Cd and Zn complexes were soluble in the organic phase. A surface decomposition rate constant of the free ligand in the organic phase of 4?10^?8m/s was obtained.     

Removal of Color and Organic Matter in Industrial Phosphoric Acid by Ozone: Effect on Activated Carbon Treatment

Industrial phosphoric acid at 42-45% P₂O₅ and containing organic matter (OM) in the range of 220 mg/L to 300 mg/L is treated by combined ozonation and activated carbon. Ozonation alone removes the initial dark color of the acid and eliminates the organic content. Adsorption on activated carbon alone can reduce OM levels by 80% for more than 25 g/kg P₂O₅. We find that a preozonation noticeably enhances activated carbon efficiency and reduces its specific consumption. Isoconversion curves are plotted in specific ozone and activated carbon ratio space.     

Investigation of the changes of P2O5 content of phosphate rock during simultaneous calcination/sulfation

In this study, the changes of P₂O₅ content of phosphate rock during simultaneous calcination/sulfation in a fluidized-bed were investigated. P₂O₅ determination was carried out on samples with and without quenching of sulfated rock. The effects of the temperature and particle size on P₂O₅ content of either sample were determined. It was found that the decrease in process temperature favorably increased the P₂O₅ content of the sulfated samples. Since the calcination was the dominant reaction during the early stages of the process, there was an initial increase in P₂O₅ content of the sulfated samples. However, at later stages, there was a decrease in P₂O₅ extent of sulfated samples with an increase in the extent of CaSO₄ formed during the reaction. The P₂O₅ extent, on the other hand, increased with decreasing particle size. The results showed that P₂O₅ content of 23.27% in raw ore may be increased up to 36% following the quenching of sulfated samples.     

Investigation of electrodeless conductivity as a technique for monitoring sulfate levels during production of wet-process phosphoric acid

In the production of wet-process phosphoric acid (WPA), sulfate concentrations influence both the crystal form and growth rate of calcium sulfate and hence the filtration rate for separating calcium sulfate from the product WPA. The filtration rate must be rapid to maintain high rates for the production of WPA. One approach for continuously monitoring sulfate concentrations during production of WPA is to measure the electrical conductivity, temperature, and specific gravity of WPA, and then relate these data to the sulfate concentration using regression equations. An electrodeless conductivity probe was used to provide reproducible conductivity measurements in return acids (12–32% P₂O₅) used for the production of WPA (24–36% P₂O₅). The effect of iron, aluminum, and magnesium impurities on the conductivity measurements was also evaluated. Regression equations were developed from the data which can be used to accurately calculate P₂O₅ and sulfate concentrations in return acids within a specified temperature range.     

ACTINIDE PARTITIONING FROM HLW IN A CONTINUOUS DIDPA EXTRACTION PROCESS BY MEANS OF CENTRIFUGAL EXTRACTORS

ABSTRACT

An experiment on actinide partitioning from real high level waste (HLW) was performed in a continuous process by extraction with diisodecylphosphoric acid (DIDPA) using a battery of 12 centrifugal extractors installed in a hot cell. The HNO₃ concentration of the HLW was adjusted to 0.5 M by dilution. The extraction section had 8 stages, and H₂O₂ was added to extract Np effectively. After extraction, Am and Cm were back-extracted with 4 M HNO₃ in 4 stages and Np and Pu were stripped with 0.8 M H₂C₂O₄ in 8 stages.

The actinides, except Np, were extracted from HLW with a very high yield. Although only 84 % of the Np were recovered in the present experiment, the recovery would be improved to 99.7 % by increasing the temperature to 45°C, the number of stages from 8 to 16 and the H₂O₂ concentration from 1 M to 2 M. Long-lived Tc and the main heat and radiation emitters Cs and Sr were not extracted and were thus separated from the actinides with high decontamination factors.

About 98 % of Am and Cm were recovered from the loaded solvent in the first stripping step with 4 M HNO₃. About 86 % of Np and about 92 % of Pu were back-extracted with 0.8 M H₂C₂O₄. These incomplete recoveries would be improved by increasing the number of stages and by optimizing the other process parameters.     

Mineralogical,chemical and solubility variations in the Eppawala phosphate deposit of Sri Lanka — a case for selective mining for fertilizers

The Eppawala phosphate deposit of Northcentral Sri Lanka is a large deposit with an estimated reserve of more than 40 000 000 metric tonnes of the ore. Field observations at Eppawala have helped to recognize several types of phosphate material on the basis of colour, texture and structure. Laboratory studies have established variable apatite mineralogies, P₂O₅ compositions and consequent variations in solubility in different segments of the phosphate body. In some selected phosphate samples from Eppawala the combined aluminium and iron percentages (Al₂O₃ + Fe₂O₃ = R₂O₃) and MnO₂ showed remarkably low values in contrast to earlier reported high values. The single apatite crystals which form at least 30% of the ore with P₂O₅ values of more than 40% and R₂O₃ contents in the range of 1% suggest their suitability for wet process production of phosphoric acid. On the basis of our findings selective mining is recommended for the Eppawala ore which is currently mined indiscriminately without due consideration being given to the heterogeneity and the anatomy of the deposit.     

Modern concept of acoustic emission (AE) coupled with electrochemical measurements for monitoring the elastomer-coated carbon steel damage in phosphoric acid medium

Elastomer coatings (rubber) are industrially used to protect phosphoric acid storage tanks against corrosion. Rubber constitutes a barrier against the penetration of H₃PO₄ to metallic surface. Coatings damage induces both acid infiltration and steel corrosion. In this concept, acoustic emission (AE) monitoring technique could be used for the detection of coatings damage as well as for steel corrosion under the coating. In the present work AE was coupled to electrochemical measurements (EM) for rubber damage evaluation and steel corrosion on three types of steels (XC48, E20 and A60) at room temperature in concentrated phosphoric acid (30% P₂O₅) contaminated by Cl⁻, F⁻, SO₄²⁻. Electrochemical behaviour of steels was studied and characterized by potentiodynamic curves and polarization resistance measurement. A good correlation between acoustic emission and polarization resistance or corrosion potential measurements was found during stages of coatings damage and steels corrosion. The majority of AE activity recorded during experiments is related to hydrogen bubbles release. The release of hydrogen bubbles gives rise to two populations of signals: one impulsive and another one resonant.     

EXTRACTION OF NEPTUNIUM WITH DI-ISODECYL PHOSPHORIC ACID FROM NITRIC ACID SOLUTION CONTAINING HYDROGEN PEROXIDE

Extraction of Np with di-isodecyl phosphoric acid (DIDPA) from HN03 solution containing H₂O_2> was studied from the aspect of the extraction mechanism and the enhancement of the extraction rate. Neptunium initially in the pentavalent oxidation state can be extracted into DIDPA even without any redox agents, but the extraction rate is rather slow. In the present work, H₂O₂ was found to accelerate the extraction. The rate was almost proportional to the 1/2-power of H₂O₂ concentration. Dependence of the extraction rate on HN03 concentration was also examined.

Neptunium extracted into DIDPA from 0.5 M HN03 solution containing H₂O₂ was found to be in the tetravalent state in the organic phase, whereas neptunium in aqueous phase was in the pentavalent state. Reduction of Np(V) with H₂O₂ occurs rapidly in the presence of DIDPA. When the concentration of HNO3 was 4 M. the neptunium extracted was also tetravalent, but the reduction of NP(V) in an aqueous solution was also observed.     

Application of Single-Ion Activity Coefficients to Determine the Solvent Extraction Mechanism for Components of High-Level Nuclear Waste

Abstract

The TRUEX solvent extraction process is being developed to remove and concentrate transuranic (TRU) elements from high-level and TRU radioactive wastes that are currently stored at U.S. Department of Energy sites. Phosphoric acid is one of the chemical species of concern in the application of solvent extraction processes for removal of actinides, for instance at the Hanford site, where bismuth phosphate was used to recover plutonium.

The mechanism of phosphoric acid extraction with TRUEX-NPH solvent at 25°C was determined from phosphoric acid distribution ratios, which were measured by using a phosphoric acid radiotracer and a variety of aqueous phases containing different concentrations of nitric acid and nitrate. A model was developed for predicting phosphoric acid distribution ratios as a function of the thermodynamic activities of nitrate ion, and hydrogen ion. The Generic TRUEX Model (GTM) was used to calculate these activities based on the Bromley method. The derived model supports extraction by CMIO and TBP in TRUEX-NPH solvent of a phosphoric acid-nitric acid complex and a CMPO-phosphoric acid complex.