Assessment of Trace Metals (TMs) in Fertilizers Formulated from Phosphate Slimes through the Progressive Substitution of Phosphoric Acid

Abstract

As part of valorizing ICS slimes, chemical fertilizers were produced according to 6-20-10, 15-10-10, and 15-15-15 formulas. Their quality was evaluated based on parameters related to dissolution, in particular conductivity, solubility, and pH. This dissolution releases chemical elements and induces the deposition of trace metals (TMs). The analysis of the samples provided key parameters essential for understanding the behavior of the fertilizer. The concentrations of TMs were measured by X-ray fluorescence spectrophotometry. Four major elements, cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb), were identified. Their concentrations varied depending on the fertilizer formulation and the proportion of slimes incorporated. Cadmium remains generally low (0 to 30.59 ppm) and complies with regulatory thresholds. Chromium shows high levels, reaching up to 404.63 ppm. Copper and lead, which are correlated, present moderate concentrations, with maximum values of 64.6 and 15.22 ppm, respectively. The measured pH is acidic and inversely correlated with conductivity. The results demonstrate the quality of fertilizers based on slimes and their compliance with agricultural standards. Environmental safety was observed for formulations containing 15% P 2 O 5 at 25% slimes substitution, while compliance depended on both fertilizer formulation and slimes substitution level.