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Purpose <p>Rock phosphate (RP) is a vital phosphorus (P) source but is limited in agricultural use due to its low solubility in soil. This review investigates the potential of low-molecular-weight organic acids, specifically oxalic, citric, and malic acids, to enhance RP solubilization. The study aims to understand the mechanisms, kinetics, and influencing factors of this process, with the ultimate goal of evaluating the applicability of organic acids for improving P bioavailability and promoting sustainable P management in agriculture.</p> Materials and methods <p>A comprehensive review of peer-reviewed literature was undertaken, focusing on studies that investigate the interaction between RP and organic acids under both laboratory and soil-based conditions. Articles were selected based on their relevance to RP solubilization mechanisms, kinetic behaviors, and influencing parameters. The review particularly examined how oxalic, citric, and malic acids enhance RP solubilization through acidification, metal chelation (Ca²⁺, Fe³⁺), ligand exchange, and electrostatic interactions. Key variables considered included pH, acid concentration, solid-to-liquid (S/L) ratio, and contact time. In addition to the qualitative synthesis, a standardized secondary data analysis was performed on phosphorus release from RP using seven different organic acids, integrating more than 400 data points extracted from eight peer-reviewed studies. Regression modeling demonstrated that oxalic and citric acids were the most effective solubilizers, with oxalic acid exhibiting superior performance under low-concentration, extended-duration conditions. These revisions ensure that the abstract aligns coherently with the rest of the manuscript and maintains a consistent narrative flow.</p> Results and discussion <p>Organic acids significantly improve RP solubilization via multiple pathways. Acidification lowers pH, enhancing P release, while chelation and ligand exchange remove metal cations from the RP matrix. Solubilization typically exhibits biphasic kinetics, an initial rapid release of P followed by a slower, sustained phase. Among the acids studied, oxalic acid showed the highest solubilization efficiency due to its strong chelating properties. The process is sensitive to physicochemical conditions, with optimal performance observed at lower pH levels, higher acid concentrations, and suitable S/L ratios. The variability in efficiency among different acids and experimental setups highlights the need for condition-specific application strategies. Oxalic acid demonstrated the highest P release efficiencies, showing a strong time-dependent response and potential inhibition at high concentrations due to calcium oxalate precipitation. Comparative modelling and contour analysis confirmed the superior solubilization potential of oxalic acid under typical agronomic conditions. Among the organic acids reviewed, oxalic acid showed the highest efficiency for phosphorus release from rock phosphate, with optimal conditions reported at an oxalic acid concentration of 0.1–0.5&#xa0;mol L⁻¹, a S/L ratio of 1:20–1:50, and a reaction time of 2–6&#xa0;h, resulting in a maximum phosphorus release of up to 60–85%, depending on the rock phosphate source.</p> Conclusion <p>Organic acids offer a promising, eco-friendly alternative to chemical P fertilizers by enhancing RP solubilization and increasing P availability in soils. Their application can contribute to more sustainable agricultural practices, reducing environmental risks associated with synthetic fertilizers. Future research should focus on field-level validation and formulation strategies to optimize organic acid use for different soil types and cropping systems.</p>

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Mechanistic and kinetic insights into organic acid-mediated rock phosphate solubilization for sustainable phosphorus mobilization

  • 期刊论文

  • 发表日期：

    2026年3月14日

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  • Sanduni Dabare,
  • Imalka Munaweera

摘要

Purpose

Rock phosphate (RP) is a vital phosphorus (P) source but is limited in agricultural use due to its low solubility in soil. This review investigates the potential of low-molecular-weight organic acids, specifically oxalic, citric, and malic acids, to enhance RP solubilization. The study aims to understand the mechanisms, kinetics, and influencing factors of this process, with the ultimate goal of evaluating the applicability of organic acids for improving P bioavailability and promoting sustainable P management in agriculture.

Materials and methods

A comprehensive review of peer-reviewed literature was undertaken, focusing on studies that investigate the interaction between RP and organic acids under both laboratory and soil-based conditions. Articles were selected based on their relevance to RP solubilization mechanisms, kinetic behaviors, and influencing parameters. The review particularly examined how oxalic, citric, and malic acids enhance RP solubilization through acidification, metal chelation (Ca²⁺, Fe³⁺), ligand exchange, and electrostatic interactions. Key variables considered included pH, acid concentration, solid-to-liquid (S/L) ratio, and contact time. In addition to the qualitative synthesis, a standardized secondary data analysis was performed on phosphorus release from RP using seven different organic acids, integrating more than 400 data points extracted from eight peer-reviewed studies. Regression modeling demonstrated that oxalic and citric acids were the most effective solubilizers, with oxalic acid exhibiting superior performance under low-concentration, extended-duration conditions. These revisions ensure that the abstract aligns coherently with the rest of the manuscript and maintains a consistent narrative flow.

Results and discussion

Organic acids significantly improve RP solubilization via multiple pathways. Acidification lowers pH, enhancing P release, while chelation and ligand exchange remove metal cations from the RP matrix. Solubilization typically exhibits biphasic kinetics, an initial rapid release of P followed by a slower, sustained phase. Among the acids studied, oxalic acid showed the highest solubilization efficiency due to its strong chelating properties. The process is sensitive to physicochemical conditions, with optimal performance observed at lower pH levels, higher acid concentrations, and suitable S/L ratios. The variability in efficiency among different acids and experimental setups highlights the need for condition-specific application strategies. Oxalic acid demonstrated the highest P release efficiencies, showing a strong time-dependent response and potential inhibition at high concentrations due to calcium oxalate precipitation. Comparative modelling and contour analysis confirmed the superior solubilization potential of oxalic acid under typical agronomic conditions. Among the organic acids reviewed, oxalic acid showed the highest efficiency for phosphorus release from rock phosphate, with optimal conditions reported at an oxalic acid concentration of 0.1–0.5 mol L⁻¹, a S/L ratio of 1:20–1:50, and a reaction time of 2–6 h, resulting in a maximum phosphorus release of up to 60–85%, depending on the rock phosphate source.

Conclusion

Organic acids offer a promising, eco-friendly alternative to chemical P fertilizers by enhancing RP solubilization and increasing P availability in soils. Their application can contribute to more sustainable agricultural practices, reducing environmental risks associated with synthetic fertilizers. Future research should focus on field-level validation and formulation strategies to optimize organic acid use for different soil types and cropping systems.