Effect of Iodide Ion Concentration on the Physicochemical Properties of Aqueous Sodium Phosphate Solutions as Fertilizer

This study aims to investigate the physicochemical properties of fertilizers containing sodium phosphate and sodium iodide salt. The research employs a hygrometric method to analyze properties of the NaI–NaH₂PO₄–H₂O ternary system at 298.15 K from dilution (0.2 mol kg^–1) to about saturated solution and for different ionic-strength fractions y of NaI (y = I_NaI/(\({{I}_{{{\text{Na}}{{{\text{H}}}_{{\text{2}}}}{\text{P}}{{{\text{O}}}_{{\text{4}}}}}}}\) + I_NaI)) with y = 1/4, 1/3, 1/2, 2/3, 3/4. The obtained data allow the deduction of diverse thermodynamic properties of the system (water activity, osmotic coefficient). Experimental results were compared with predictions from four models (Dinane’s ECA, Lin et al., Robinson and Stokes (RS) and Lietzke and Stoughton (LS II). Additionally, the Pitzer–Simonson–Clegg (PSC) model was used to correlate the data for determining binary and ternary interionic parameters for predicting solute activity coefficients of solutes and excess Gibbs energy G^ex of the NaH₂PO₄–NaI–H₂O at different compositions. This analysis enhances our understanding of the influence of NaI on phosphate-based fertilizer systems, offering crucial insights for developing fertilizers aimed at improving agricultural productivity and fostering sustainable farming practices.