Thermal pretreatment and incongruent dissolution of Lac à Paul apatite: Implications for phosphorus bioavailability and carbon sequestration

• Heated apatite (800 °C) releases 33 % more phosphorus than unheated samples in dissolution. • No physical changes in apatite grains due to thermal pretreatment, even at micrometer scale. • Incongruent dissolution favoring calcium: potential for CO 2 sequestration. • Etch pits formed by acid attack reveal active dissolution on apatite grain surfaces. A growing global population and climate change pose significant challenges to sustainable agriculture, requiring innovative approaches to fertilizer production and carbon sequestration. This study investigates the potential of thermally-treated igneous apatite from the Lac à Paul magmatic deposit (Québec, Canada) as an environmentally friendly alternative to conventional phosphate fertilizers. The research examines the physical and chemical transformations of heated apatite concentrate, focusing particularly on phosphorus release mechanisms and carbon sequestration potential. Heat treatment at 800 °C demonstrated the highest phosphorus liberation after 30 min, although concentrations remained lower than conventional fertilizers (129.8 mg/L for UQC2 versus 1171.1 mg/L for NPK 10–52-10); Scanning electron microscopy revealed the formation of etch pits on acid-attacked grains within 30 min of reaction, indicating rapid surface modification. Notably, the dissolution process exhibited early-stage incongruency favoring calcium release, with concentrations reaching 330 mg/L. This preferential calcium liberation suggests potential for CO 2 sequestration through carbonate mineral formation in the soil. Although the immediate phosphorus availability from heated igneous apatite is lower than conventional fertilizers, its geochemical stability favors sustained nutrient release capabilities in the longer term. Furthermore, the low concentration of contaminants (U, Th, Cd) in igneous apatite relative to sedimentary sources makes igneous apatite particularly suitable for agricultural applications. Our findings contribute to the development of sustainable fertilizer alternatives that could simultaneously address agricultural productivity and climate change mitigation through carbon sequestration and offer insights into the intricate relationship between mineral composition and nutrient availability.