Oxalic acid is more efficient than sulfuric acid for rock phosphate solubilization

• Published in: Minerals engineering Vol. 155; p. 106458
• Main Authors: Mendes, Gilberto de Oliveira, Murta, Hiunes Mansur, Valadares, Rafael Vasconcelos, Silveira, Wendel Batista da, Silva, Ivo Ribeiro da, Costa, Maurício Dutra
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.08.2020
• Subjects: Bioleaching; Fertilizer; Phosphorus; Phosphorus; Bioleaching; Fertilizer
• ISSN: 0892-6875; 1872-9444
• DOI: 10.1016/j.mineng.2020.106458

•Oxalic acid extracts 100% of P from rock phosphates.•Compared to sulfuric acid, lower amount of oxalic acid is required to solubilize P.•Oxalic acid is a biotechnological alternative to produce P fertilizer. Organic acids produced by microorganisms have been proposed as a biotechnological tool to release phosphorus (P) from sparingly soluble rock phosphates (RPs). In this work, organic acids commonly associated with microbial P solubilization (citric, gluconic, itaconic, malic, and oxalic) were applied at increasing doses to solubilize RPs with distinct reactivity grades. P solubilization by organic acids was compared to sulfuric acid, the traditional reagent applied in RP solubilization for fertilizer production. The acid type and its concentration had more influence on solubilized P than RP reactivity. In general, the efficiency of organic acids was oxalic > citric ≥ malic > itaconic > gluconic. Oxalic and sulfuric acids solubilized 100% of the P contained in all RPs composed by apatite [Ca5(PO4)3(OH,F,Cl)]. However, oxalic acid was superior to sulfuric acid, releasing more P per mmol of acid applied. In average, each mmol of oxalic acid released 21 mg P, while sulfuric acid solubilized 14 mg P mmol−1. Thus, microorganisms producing oxalic acid appear as a promising alternative to process RP via a biotechnological route.