Mechanism and Kinetics for the Dissolution of Apatitic Materials in Acid Solutions

Abstract

- This work concerns the study of the digestion step in the production process of phosphoric acid. Some qualitative experiments indicate that the difference between the pH at the surface of the phosphate and that in the bulk of the solution is negligible and that the dissolution is controlled by diffusion of products away from the phosphate particle. In further experiments, to isolate the dissolution phenomenon from the formation of calcium sulfate, the sulfuric acid normally used industrially is replaced by hydrochloric acid. The phosphate material used in our experiments is a model apatitic material: synthetic hydroxyapatite (HAP). The dissolution of calcium hydroxyapatite was studied with increasing amounts of calcium and phosphate at different temperatures. A simple method was developed for this observation based on the time required for complete dissolution of the HAP powder. The results confirm that the dissolution is controlled by a diffusional process through an interface of calcium and phosphate ions released from the solid surface. A kinetic model for the dissolution of apatitic materials is proposed which assumes a shrinking particle behaviour controlled by diffusion of calcium ions. The experimental results are fitted to this model to determine the mass transfer constant for HAP dissolution in acid solutions. The activation energy of the reaction is about 14kJ/mol. This study was carried on in conditions similar to the industrial ones for the production of phosphoric acid by the dihydrate-proces

Opportunities to Alleviate Soil Acidity Impact Through Exploitation of Diverse Liming Materials Integrated with Different Phosphatic Fertilizer Sources in Ethiopia

“…Deposits that could be mined and processed economically to give about 28-38% P2O5 are considered commercial phosphate deposits (Sengul et al, 2006). However, phosphate rocks decomposition by sulfuric acid remains the most widely used method (Sinirkaya et al, 2014) and over 90% phosphoric acid produced worldwide is manufactured by digestion of phosphate rocks with sulfuric acid (Calmanovici et al, 1997). The phosphate rocks are decomposed by sulfuric acid in the manufacturing units of phosphate fertilizers according to the following reaction (Becker, 1989)…”

“…Production of ammonium polyphosphate fertilizer (APP) requires dehydration and polymerization of phosphoric acid prior to ammoniation. This polymerization is accomplished by the dehydration of phosphoric acid (Calmanovici et al, 1997). The most common commercially available inorganic P fertilizers are DAP, MAP, and APP.…”

Dissolution of Tunisian phosphate ore by a mixture of sulfuric and phosphoric acid: Kinetics study by means of differential reaction calorimetry

“…Several studies on the dissolution of synthetic phosphate [5][6][7][8][9][10][11][12] or phosphate ore [13][14][15][16][17][18][19][20][21][22][23] in acid solutions have been carried out such as phosphoric acid [5,[15][16][17], succinic acid [18], acetic acid [19], and hydrochloric acid [6,[20][21] to illustrate the kinetics and process mechanism as well as enhancing the yield of the phosphate attack. Nevertheless, phosphate ore dissolution by sulfuric acid remains the most extensively used process [22] and over 90% of the phosphoric acid produced globally is manufactured through the decomposition of phosphate ore with sulfuric acid as an acidulate [23]. The decomposition of phosphate rocks using aqueous sulfuric acid has been studied by several authors [24][25][26][27][28][29][30][31].…”

Attack of Tunisian Phosphate Ore by a Mixture of Sulfuric and Phosphoric Acid: Thermochemical Study by Means of Differential Reaction Calorimetry

“…It is well know that natural phosphates cannot be used directly as a fertilizer because of their insolubility to make them available to plants, phosphate are dissolved by acids. A number of published studies devoted to phosphate synthetic [9]- [16] or natural [17]- [37] in single aqueous acid solutions were carried such as phosphoric acid [10] [23], succinic acid [24], nitric acid [28] and hydrochloric acid [9] [13] [26] [27] or mixture acid solution [33] [34] [35] [36] in literature to clarify the kinetics and process mechanism and improve the performance of phosphate attack. However, phosphate rocks decomposition by sulfuric acid remains the most widely used method [29] [30] [21] [32] and over 90% of the phosphoric acid produced worldwide is manufactured by digestion of phosphate rocks with sulfuric acid as an acidulant [37].…”