Dissolution of Calcareous Phosphate Rock from Gafsa (Tunisia) Using Dilute Phosphoric Acid Solution (original) (raw)
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Special Topics & Reviews in Porous Media - An International Journal, 2010
The reactivity of calcined Tunisian phosphate ore was studied in both phosphoric and acetic solutions. Phase analysis from X-ray diffraction and IR absorption data indicate that carbonate apatite, or francolite, and fluorapatite are the main phases. However, it was observed that the calcium oxide phase, evident at the most intense peak (d=2.401Å;2θ= 37.42 •) and at the adsorbant band at around 700 cm −1 disappeared or were weakly defined for the solid leached in acetic medium. Nitrogen adsorption-desorption analysis shows a rising of mesopores at the surface of the leached particles and then an increase of their specific surface area, SBET. The scanning electron microscope micrographs of the particles and their size distribution show a constancy of their outer dimensions during attack.
Journal of Colloid and Interface Science, 2002
a reaction time of 60 min for dissolution at 25ЊC, a stirring A detailed mechanism of the selective dissolution of calcite from speed of 200 rpm, an acetic acid concentration of 1 M, low-grade phosphate ores (Epirus area, Greece), using dilute aceparticle size fraction of 250-500 mm, and 1.25 stoichiometic acid, and a model equation which fitted the experimental data try. These experimental conditions led to a phosphate conperfectly, are presented in this report. The model equation has the centration of about 31% for P 2 O 5 or 95% for francolite. form y Å C 1 re r 1 rt / C 2 re r 2 rt of a double exponential decay, where During the dissolution process dissolved mainly the calcite r 1 and r 2 are relations of the rate constants k 2 and k 4 of the slow spaces, while almost all of the francolite remained in the reactions in the dissolution mechanism. By suggesting some reasolid phase. The pseudohomogeneous first-order reaction kisonable postulates based on this work, we estimated the values netics models have been found to express the experimental of k 2 and k 4 from r 1 and r 2 ; consequently, we deduced that the transformation of H 2 CO 3 to CO 2 (gas) is most likely to be the rate-data. controlling step of the overall mechanism. Finally, the analysis of In this paper we describe a detailed mechanism and we our experimental data according to three different tests showed develope a model equation which can describe the selective that the controlling step of this heterogeneous reaction is a chemidissolution of calcite from the low-grade phosphate ores cal change.
Exploration of mesoporous structure of tunisian raw and acid-leached phosphate ore particles
Canadian Journal of Chemical Engineering, 1997
Rock phosphate fractions were examined for their porous structure by nitrogen adsorption. The pore size distribution and the shape of pores does not seem to depend on the particle size. The specific surface area values present two regions, one above and one below that of the particles with 125 pm diameter. Particles of a given size were leached with dilute phosphoric acid (1.5 mass% P,O,) at 25°C. It was observed that there is a widening of the initial pores during leaching. The particles collected at the initial period of the reaction are pitted and those collected at the final period are disintegrated. On a examine la structure poreuse de fractions de phosphate de roche par adsorption de I'azote. La distribution de la taille des pores et la forme des pores ne semblent pas dependre de la taille des particules. Les valeurs de surface specifique presentent deux regions, I'une au-dessus et I'autre en-dessous de celle des particules d'un diametre de 125 pm. Les particules d'une taille donnee ont ete lessivees a l'acide phosphorique dilue (1 3 % de P,O, en masse) a 25°C. On a observe un elargissement des pores initiales lors du lessivage. Les particules collectees au debut de la reaction sont cor-rod& et les particules collectees a la fin desintegrees.
Journal of Colloid and Interface Science, 1998
a reaction time of 60 min for dissolution at 25ЊC, a stirring A detailed mechanism of the selective dissolution of calcite from speed of 200 rpm, an acetic acid concentration of 1 M, low-grade phosphate ores (Epirus area, Greece), using dilute aceparticle size fraction of 250-500 mm, and 1.25 stoichiometic acid, and a model equation which fitted the experimental data try. These experimental conditions led to a phosphate conperfectly, are presented in this report. The model equation has the centration of about 31% for P 2 O 5 or 95% for francolite. form y Å C 1 re r 1 rt / C 2 re r 2 rt of a double exponential decay, where During the dissolution process dissolved mainly the calcite r 1 and r 2 are relations of the rate constants k 2 and k 4 of the slow spaces, while almost all of the francolite remained in the reactions in the dissolution mechanism. By suggesting some reasolid phase. The pseudohomogeneous first-order reaction kisonable postulates based on this work, we estimated the values netics models have been found to express the experimental of k 2 and k 4 from r 1 and r 2 ; consequently, we deduced that the transformation of H 2 CO 3 to CO 2 (gas) is most likely to be the rate-data. controlling step of the overall mechanism. Finally, the analysis of In this paper we describe a detailed mechanism and we our experimental data according to three different tests showed develope a model equation which can describe the selective that the controlling step of this heterogeneous reaction is a chemidissolution of calcite from the low-grade phosphate ores cal change.
A review of the beneficiation of calcareous phosphate ores using organic acid leaching
Hydrometallurgy, 2010
The beneficiation of phosphate ores containing carbonate gangue by conventional techniques such as physical separation methods or flotation is very difficult due to the similarities in physico-chemical properties of constituent minerals present in the system. Carbonate-rich phosphate deposits can be processed by calcination and by selective acid leaching methods. However, calcination has some drawbacks and selective leaching with organic acids is a promising method for the beneficiation of this type of ore. In this paper, the leaching of calcareous phosphate ores proposed in the literature is reviewed with the aim of identifying the important factors involved in the dissolution process. The literature indicates that the organic acid reagent, acid concentration, reaction time, solid/liquid ratio, temperature, particle size distribution and stirring speed are important parameters in the process. The range and optimum values of these parameters reported in the literature are summarized, but there is still some doubt regarding the optimum reaction time. Analysis of the leaching kinetic data and activation energy show that the leaching reaction is chemically controlled. Limited consideration is given to the economic aspects of organic acid leaching. The leaching method appears to be cheap, but a complete economic evaluation is required for each ore, dependent upon the local price of the organic acids used and the cost of their recovery. It is proposed that future research should focus on the leaching characteristics of specific calcareous phosphate ores and on the development of a methodology to optimise leaching using organic acids.
Abu-Eishah, S.I., E1-JaUad, I.S., Muthaker, M., Touqan, N. and Sadeddin, W., 1991. Beneficiation of calcareous phosphate rocks using dilute acetic acid solutions: optimisation of operating conditions for Ruseifa (Jordan) phosphate. Int. J. Miner. Process., 31: 115-126.
Sorption of phosphate onto calcite; results from batch experiments and surface complexation modeling
Geochimica et Cosmochimica Acta, 2011
The adsorption of phosphate onto calcite was studied in a series of batch experiments. To avoid the precipitation of phosphate-containing minerals the experiments were conducted using a short reaction time (3 h) and low concentrations of phosphate (650 lM). Sorption of phosphate on calcite was studied in 11 different calcite-equilibrated solutions that varied in pH, P CO 2 , ionic strength and activity of Ca 2+ , CO 2À 3 and HCO À 3. Our results show strong sorption of phosphate onto calcite. The kinetics of phosphate sorption onto calcite are fast; adsorption is complete within 2-3 h while desorption is complete in less than 0.5 h. The reversibility of the sorption process indicates that phosphate is not incorporated into the calcite crystal lattice under our experimental conditions. Precipitation of phosphate-containing phases does not seem to take place in systems with 650 lM total phosphate, in spite of a high degree of super-saturation with respect to hydroxyapatite (SI HAP 6 7.83). The amount of phosphate adsorbed varied with the solution composition, in particular, adsorption increases as the CO 2À 3 activity decreases (at constant pH) and as pH increases (at constant CO 2À 3 activity). The primary effect of ionic strength on phosphate sorption onto calcite is its influence on the activity of the different aqueous phosphate species. The experimental results were modeled satisfactorily using the constant capacitance model with >CaPO 4 Ca 0 and either >CaHPO 4 Ca + or >CaHPO À 4 as the adsorbed surface species. Generally the model captures the variation in phosphate adsorption onto calcite as a function of solution composition, though it was necessary to include two types of sorption sites (strong and weak) in the model to reproduce the convex shape of the sorption isotherms.
Solubility test in some phosphate rocks and their potential for direct application in soil
2009
There are various methods to evaluating phosphate rock for direct application. The first approach is solubility test of Phosphate Rocks (PR) using chemical extractant. In this study to compare the effectiveness of direct application of PRs, two samples of a sedimentary unbeneficiated PR from Lar mine of Yasooj and two samples of concentrated PR of Asfordi igneous PR of Yazd in Iran along with one sample PR of Gafsa (Tunisia) were analyzed for the main nutrients and minerals with XRF and XRD. Calcite and quartz were the main ingredients of Yasooj PR which cause problems for direct application. Yazd PR in addition to apatite had some iron and magnesium minerals which are also undesirable for fertilizer producing. The reactivity of these PRs was determined using the common extractants (Formic Acid, Citric Acid and Neutral Ammonium Citrate) and classified on the basis of International Fertilizer Development Center (IFDC) proposed classification method for direct application. The reactivity of Iranian PRs was quite low compare to Gafsa PR. The long-term dissolution kinetics of these PRs were determined with Formic Acid (FA) and Citric Acid (CA) showed slow reaction initially (0-20 min.) because of the presence of free calcium carbonate but later on the reaction rate increased surpassing Gafsa PR. Therefore Yasooj PR could be recommended to use in soil after beneficiation and removal of lime. The kinetics of dissolution of Yazd PRs followed a zero order equation.
Industrial & Engineering Chemistry Research, 1996
This paper is devoted to the fundamentals of natural phosphate rock dissolution under conditions close to those in the industry of the wet-process phosphoric acid production. The dissolution kinetics and mechanism of single crystals of natural fluorapatite at micro- and nanolevels have been studied for the first time. Methods of optical and scanning electron microscopy and Auger electron and IR reflection spectroscopy were used for the investigations. As a result, effects of dislocation acceleration of dissolution rate (increasing to 1.6 times) and random fluctuations of crystal size with parameter 1.15 ± 0.05 μm were discovered. Both phenomena have been described as a micromechanism of dissolution. A new system of five chemical equations for the acidic dissolution of fluorapatite has also been proposed and described as a nanomechanism of dissolution. The obtained results are useful for elaboration of new technological and ecological principles of wet-process phosphoric acid production.