Contamination of corn growing areas due to intensive fertilization in the High Plane of Mexico

The agricultural activities practice often demands an intensive application of fertilizers. Phosphate and nitrogen fertilizers are the most employed in the corn growing areas of the central Mexico highlands. The first ones presents an uranium content ranging from 50 to 200 mg · kg−1 depending on the origin of the phosphate rock used in its production. It is crucial to analyze the rainwater, surface water, soil water at several depths, groundwater and soil to determine the simultaneous behavior of phosphate, nitrate and uranium, and their leaching in a specific agricultural land. Uranium concentration, 16 mg · kg−1, in the soil water was higher than that in the surface water and groundwater. The different concentrations are due to an unequal uranium distribution in the environment. The phosphate concentration, 37.4 mg · kg−1, diminished throughout the profile of the soil due to a sorption–precipitation process. The nitrates were leached toward groundwater after the application of fertilizers, but the nitrate concentration in it did not exceed the limit for drinking wáter

Uranium and phosphate behaviour in the vadose zone of a fertilised corn field

Phosphate fertilizers contain approximately 200 mg.kg–1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1–50 mg.k –1) and phosphates (22–33 mg.kg–1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg.l–1 and phosphates between 1 and 0.3 mg.l–1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved

Spectroscopic Determination of Optimal Hydration Time of Zircon Surface

When a mineral surface is immersed in an aqueous solution, it develops an electric charge produced by the amphoteric dissociation of hydroxyl groups created by the hydration of the solid surface. This is one influential surface property. The complete hydration process takes a time which is specific for each mineral species. The knowledge of the aqueous solution contact time for complete surface hydration is mandatory for further surface phenomena studies. This study deals with the optimal hydration time of the raw zircon (ZrSiO4) surface comparing the classical potentiometric titrations with a fluorescence spectroscopy technique. The latter is easy and reliable as it demands only one sample batch to determine the optimal time to ensure a total hydration of the zircon surface. The analytical results of neutron activation analysis (NAA) showed the presence of trace quantities of Dy3+, Eu3+ and Er3 in the bulk of zircon. The Dy3+ is structured in the zircon crystalline lattice and undergoes the same chemical reactions as zircon. Furthermore, the Dy3+ has a good fluorescent response whose intensity is enhanced by hydration molecules. The results show that, according to the potentiometric analysis, the hydration process for each batch (at least 8 sample batches) takes around 2 h, while the spectrometric method indicates only 5 min from only one batch. Both methods showed that the zircon surface have a 16h optimal hydration time

Interaction of salicylic acid with zirconium diphosphate and its reactivity toward uranium (VI)

International audienceThe interaction of salicylic acid with zirconium diphosphate surface and its reactivity toward uranium (VI) was investigated. The interaction of salicylic acid with zirconium diphosphate was firstly studied using several analytical techniques including atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The sorption of uranium (VI) onto surface modified zirconium diphosphate was evaluated by the classical batch method at room temperature. This study showed that the uranium (VI) sorption onto zirconium diphosphate is influenced by the presence of salicylic acid. A fluorescence spectroscopy study revealed the presence of a uranyl specie onto the modified solid surface. The spectroscopy results were then used to restrain the modeling of experimental sorption data, which are interpreted in terms of a constant capacitance model using the FITEQL code. The results indicated that interaction between the uranium (VI) and the surface of zirconium diphosphate modified with salicylic acid leads to the formation of a ternary surface complex

Titanium Pyrophosphate for Removal of Trivalent Heavy Metals and Actinides Simulated by Retention of Europium

This work addresses the synthesis of titanium pyrophosphate, as well as the characterization and evaluation of the sorption process of europium, for removal of trivalent heavy metals and actinides simulate. The evaluation of the surface properties of titanium pyrophosphate was carried out determining the surface roughness and surface acidity constants. The values obtained from the determination of the surface roughness of the synthesized solid indicate that the surface of the material presents itself as slightly smooth. The FITEQL program was used to fit the experimental titration curves to obtain the surface acidity constants: log⁡K+=3.59±0.06 and log⁡K-=-3.90±0.05. The results of sorption kinetics evidenced that the pseudo-order model explains the retention process of europium, in which the initial sorption velocity was 8.3 × 10−4 mg g−1 min−1 and kinetic constant was 1.8 × 10−3 g mg min−1. The maximum sorption capacity was 0.6 mg g−1. The results obtained from sorption edge showed the existence of two bidentate complexes on the surface