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

Abstract

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%.

Enhancing chemical properties and maize yield through dolomite application on rock phosphate-amended oxisol

“…Soil pH increased to 0.47, 0.79, and 0.97 units at 15, 30, and 90 DAP respectively. This current research is in line with several studies, where the application of dolomite can increase soil pH [17][18][19][20] Morocco rock phosphate contains 27.70% -31.20 P2O5 [21,22]. Rock phosphate application will significantly affect soil with low pH (<5.5).…”

Enhancing the Concentration of Nodular Phosphoriteby Selective Leaching

“…One of these factors is the CaO/P 2 O 5 weight ratio, which determines the amount of sulfuric acid needed to acidulate the phosphate rock in the manufacture of wet-process acid. The CaO/P 2 O 5 weight ratio is a widely used measure of the quality of phosphate rock, with a ratio of 1.32 for pure apatite, while commercially available rock may have a CaO/P 2 O 5 ratio of up to 1.6 (Gilmour, 2013;Ryszko, 2023). In our case, this ratio is 1.05, which may require the least amount of sulfuric acid to process.…”

Phosphorus Recovery from Whole Digestate through Electrochemical Leaching and Precipitation

“…The solids were enriched with P under all current densities, with a P content of 12.41−14.63% (Figure 4B), or 28.42− 33.51% as P 2 O 5 that fell in the range for high-grade phosphate rock and similar to the value reported in a three-chamber electrochemical nutrient recovery cell. 10,50 The highest calcium content (29.53%) and Ca/P molar ratio (1.61) in suspended solids were observed under 5 A m −2 , compared to 19.69− 22.04% and 1.14−1.24 for current densities of 10−30 A m −2 (Figure 4C). The greater relative abundance of Ca in suspended solids under 5 A m −2 suggests that more calcium precipitates formed, consistent with the lowest Ca 2+ concentration in the cathode effluent (Figure S5).…”