Title : Evaluation of the efficiency of portable X-ray fluorescence (pXRF) in the chemical characterization of soil remineralizers: Comparison between filler and powder granulometry
Abstract:
Portable X-ray fluorescence (pXRF) is a non-destructive analytical technique widely used to determine the chemical composition of a wide range of materials, based on the emission of characteristic fluorescent radiation, in which the atoms constituting the irradiated sample emit a specific energy signature that enables their identification. In soil remineralizers, the quantification of oxides is particularly relevant, as these are essential for evaluating the agronomic and industrial potential of such materials, based on the analytical parameters established by Law No. 12,890 of December, 2013, and Normative Instruction No. 5 of March, 2016 of Brazil. The objective of this study was to evaluate the efficiency of pXRF in determining macronutrients in remineralizers., considering the influence of sample particle size (filler < 0.075 mm and powder) on the analytical results. The material analyzed was a remineralizer registered in Bahia, Brazil, commercially known as Ipirá Fértil. The study aimed to compare possible variations in oxide quantification and their implications for the chemical characterization of the material. Initially, the remineralizer was placed in Petri dishes until the surface was fully covered, one dish for each granulometry. Analyses were performed using a portable XRF spectrometer (Niton XL3t Ultra Analyzer), which was calibrated and operated using the “Test All Geo” function, with an analysis time of 120 seconds. A Sum of Bases (TBS) of 6.26% was obtained for the powder fraction, below the minimum threshold of ≥ 9% established by Normative Instruction No. 5/2016. However, the same material in the filler fraction showed a value of 11.8%. This difference is possibly associated with the greater homogeneity and surface area of finer particles, which enhances their interaction with radiation and improves the representativeness of pXRF analysis, given that both fractions share the same mineral constituents. Potassium content was similar between the two particle size fractions, with 2.66% in the filler and 2.94% in the powder. The observed difference in the total base sum (TBS) is mainly associated with CaO and MgO contents, with the filler fraction showing increases of 1.69% in CaO and 3.64% in MgO relative to the powder fraction. It is noteworthy that Ca and Mg have lower fluorescence energies, making them more susceptible to interferences and matrix absorption effects. Consequently, small variations in sample characteristics may result in more pronounced differences in the quantification of these oxides. Potentially toxic elements (Cd, As, Hg, Pb) were not detected by the instrument. Aluminum contents were low, with 5.93% in the powder and 10.34% in the filler, which is considered favorable, as this element can be toxic to plants. However, manganese content differed between fractions, with 0.1% in the powder (low) and 0.34% in the filler (moderate). In conclusion, portable X-ray fluorescence (pXRF) is an efficient technique for the chemical characterization of ground rocks with potential use as remineralizers. However, particle size significantly influences the results, with finer samples (filler) providing more reliable data due to greater homogeneity and improved interaction with incident radiation.
