Phosphorus Solubilization From Phosphate Rock Using Organic and Inorganic Acids

Phosphorus (P) is an essential element for plant growth, but its availability in soils is often limited due to the low solubility of phosphate rock (PR), a major natural P source. Acid-based solubilization is a common strategy to enhance P availability, using both inorganic acids (sulfuric acid, H2SO4; nitric acid, HNO3) and organic acids (citric acid, C6H8O7; oxalic acid, C2H2O4). This study assessed the solubilization efficiency of these acids at three different molar concentrations (0.01, 0.05, and 0.1 M) under controlled laboratory conditions. PR samples were treated with acid solutions for 24 h, and soluble phosphorus was quantified using the vanadomolybdate method. Results showed that nitric acid at 0.1 M (102 ± 3 mg L-1), sulfuric acid at 0.01 M (102 ± 1 mg L-1), and oxalic acid at 0.01 M (101 ± 2 mg L-1) exhibited comparable and high solubilization values. In contrast, citric acid at 0.01 M showed the lowest efficiency (58 ± 1 mg L-1). Analysis of variance (ANOVA) and Tukey’s test (p < 0.05) confirmed significant differences among treatments. These findings suggest that oxalic acid at a low concentration (0.01 M) may serve as an environmentally friendly alternative to strong mineral acids for PR solubilization. Furthermore, combining acid treatments with biological strategies could enhance P availability in a sustainable manner.