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Concentrations of potentially toxic elements were determined in the soil solution of two soils (acidic sandy and slightly acidic clay loam) treated with phosphate rocks having high Cd content in a pot experiment. Relative concentrations characterizing the mobility of metals (expressed as soil solution concentrations in percentage of their “total” amounts in the phosphate rock-treated soil) decreased with increasing phosphate rock rates in the sandy soil. Mn@Sr>Cd@Co were the most, while Pb and Cr the least mobile elements. The relative concentrations in the clay loam soil were much lower than in the sandy soil and they practically remained constant with increasing phosphate rock rates. It was concluded that in the experimental time frame the environmental risk did not increase with the increase of phosphate rock rate. 

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Abstract  

Uranium in phosphate rock was removed by means of alkaline leach solutions. Ammonium carbonate/bicarbonate solution produced a very stable uranyl carbonate compound which was separated by centrifugation. Radiometric analysis showed that about 40% of uranium was solubilized and it can be recuperated. This process could be used before the manufacture of phosphatic fertilizers and the final products would contain smaller uranium quantities.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
E. Romero-Guzmán
,
E. Ordoñez-Regil
, and
V. Lara Corona

Abstract  

The uranium content in ground phosphate rock was leached out with alkaline solution, however, a poor yield was obtained. XRD, TGA and -spectrometric analyses in the solid fraction showed that francolite is the main mineral in which uranium is present in different oxidation states (+4 and +6). It was found that considerable amounts of uranium and carbonate were extracted from francolite, which suggests the presence of different uranium compounds in the bulk.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
E. Romero Guzmán
,
M. Solache Ríos
,
J. Iturbe García
, and
E. Ordoñez Regil

Abstract  

It is well known that phosphate rock contains a small amount of uranium. During the production of phosphate fertilizers, most uranium present is found in the phosphate fraction. Uranium was determined in the 70–200 ppm range in the phosphate rock and the final products by nuclear and classical methods.

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Abstract  

The substoichiometric isotope dilution analysis for U(VI) in a synergic extraction system of an excess amount of a chelating agent HHFA and a substoichiometric amount of neutral ligand TOPO has been developed. A constant but substoichiometric amout of U(VI) can be precisely extracted, and U down to ppm levels can be accurately determined by the present method. This method was applied to the analysis of a phosphate rock.

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Summary  

Phosphate deposits are generally characterized by enhanced radionuclide concentrations compared to natural levels. The mining and processing of this phosphate ore redistribute radionuclides throughout the environment and introduce them into phosphoric acid and phosphogypsum. Phosphoric acid is the starting material for triple superphosphate (TSP), single superphosphate (SSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), NPK fertilizers and di-calcium phosphate (DCP). Contents of natural radionuclides from thorium and uranium series, 226Ra, 210Pb and 228Ra, were measured in Brazilian igneous phosphate rock, phosphoric acid, phosphogypsum and phosphate fertilizer samples, using high-resolution gamma-spectrometry. Neutron activation analysis was used for the determination of U and Th in the same samples. The fertilizers samples which are derived directly from phosphoric acid, MAP and DAP, presented activity concentrations around the detection limits of the counting system for 226Ra (<5.0 Bq . kg-1 ), for 228Ra (<3.0 Bq . kg-1) and for 210Pb (<19 Bq . kg-1). As for U and Th, the concentrations found in MAP and DAP are more significant, up to 374 and 250 Bq . kg-1, respectively. SSP, TSP and NPK, which are obtained by mixing phosphoric acid with different amounts of phosphate rock and NH3, presented higher concentrations of radionuclides, up to 871 Bq . kg-1 for 226Ra, 283 Bq . kg-1 for 228Ra, 1255 Bq . kg-1 for 210Pb, 413 Bq . kg-1 for U and 538 Bq . kg-1 for Th.

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Abstract  

Extensive sedimentary phosphate deposits exist in the Sirhan-Turayf basin in northwestern Saudi Arabia containing significant amounts of uranium, thorium, vanadium and rare earth elements. The determination of the concentration and pattern of distribution of some of these elements is essential for economic aspects. This study reports the analysis of vanadium in selected phosphate rock samples from the basin using accelerator-based thermal neutrons activation analysis (TNAA). Samples were irradiated in a thermal neutron flux of 2.5·106 n·cm−2·s−1. The induced activity was measured with a HP-GMX detector coupled to a PC-based data acquisition and analysis system. The facility was calibrated using certified standards of vanadium. The minimum detection limit of vanadium was about 1 mg. Three independent measurements on each sample yielded comparable results indicating the reliability of the technique. The vanadium concentrations in the samples vary from 23 to 457 ppm.

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Abstract  

A relatively rapid, economic and robust procedure is described for the radiometric analysis of uranium in phosphate rock and phosphogypsum. The analysis is performed by alpha spectroscopy after pre-concentration and separation of uranium by liquid-extraction using tributyl-phosphate (30% TBP in dodecan) and finally its electrodeposition on stainless steel discs. The method has been successfully applied to 0.1 g samples of phosphate rock and phosphogypsum resulting in high-quality spectra for measurement times ≥15 h. The main advantage of the procedure is the use of tracer solution (232U) that allows reliable measurements and evaluation of the separation procedure. The separation efficiency of the proposed method has been estimated to be (75 ± 20)%.

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Acta Phytopathologica et Entomologica Hungarica
Authors:
S. Kribel
,
S. Qostal
,
A. Ouazzani Touhami
,
K. Selmaoui
,
A. Mouria
,
R. Benkirane
,
El. H. Achbani
, and
A. Douira

Thirty Trichoderma isolates isolated from compost, various crops and soil with roots of adjacent sites to the phosphate mines of Morocco, were tested in vitro for their potential to solubilize phosphorus from phosphate rock. The qualitative assessment of phosphate solubilization by Trichoderma isolates was performed on Modified Pikovskaya Agar (MPA) solid medium. The visual observation of the 3- and 6-day-old cultures did not show any clear zone around the colony. However, all the isolates were able to grow on the culture medium 3 days after incubation, the maximum recorded diameter was 58.6 mm for isolate TR-B 98 (3) and the minimum value was 34.8 mm for isolate TS-EM-98 (2). After 6 days, they showed good radial growth that exceeded 79.8 mm with variable appearance of the mycelial density such as the isolates TS-B 98, TS-EM-98 (1) and TR-CB 2000 (1) that presented, respectively, high, regular and low mycelial density. Also, the Trichoderma isolates produced variable number of conidia on MPA medium. Quantitative estimation on the Modified Pikovskaya Broth (MPB) liquid medium showed a variable potential of the Trichoderma isolates to solubilize phosphate when the amount of soluble phosphorus remained low in the liquid medium without the fungus (0.26 mgL−1). The maximum concentration of soluble phosphorus was 11.92 mgL−1 with percentage of soluble phosphorus equal to 95.39% recorded by the isolate TR-TB 2000 after 9 days of incubation, followed by the isolates TR-B 98 (3), TS-B 98 and TR-EM 2 respectively, 11.20, 10.47 and 9.61 mgL−1 and 89.6, 83.76 and 76.38%. In addition, treatments with Trichoderma isolates provided a lower final broth pH which varied between 6.81 for TOL isolate and 3.40 for TS-B-2000 (2) compared to initial pH (7.2). The isolates that proved potent for phosphate solubilization displayed the highest fresh and dry weights such as TR-TB 2000 (FW = 4.11 g and DW = 2.56 g), while the lowest fresh and dry weight were noted in the weakest isolates for phosphate solubilization such as T27 (FW = 1.025 g and DW = 0.58 g).

The high solubilization potential of Trichoderma isolates can be exploited for the solubilization of fixed phosphorus present in the soil, thus improving soil fertility and plant growth.

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Journal of Thermal Analysis and Calorimetry
Authors:
S. El Asri
,
A. Laghzizil
,
A. Alaoui
,
A. Saoiabi
,
R. M’Hamdi
,
K. El Abbassi
, and
A. Hakam

Abstract  

Moroccan phosphate ores have important phosphate reserves, thus makes possible to distinguish three main layers: submittal, principal and basal. A characterization of the ore was carried out to determine the mineralogical and chemical characteristics. Thermal analysis, infrared and NMR techniques were used to study the thermal and structure behaviors of the organic matter in Moroccan phosphate from Bengurir. The TG analysis showed that the investigated mineral exhibited 7 mass% as total mass loss. The calcination-separation enrichment of carbonate-phosphorite ores from Bengurir region (Morocco) has been studied.

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