Thermodynamic and experimental insights toward an eco-friendly phosphorus production

Abstract

High-purity phosphorus production from varying grades of phosphate ore typically involves energy-intensive and operationally complex processes. In this study, thermodynamic analyses and experimental validations were performed to evaluate the feasibility of phosphorus gas production through a sustainable process comprising thermal decomposition and smelting of phosphate ores. The thermal treatment, conducted without a reducing agent, facilitated the removal of carbon dioxide (CO₂) and heavy metals from the ore, simplifying downstream processing and reducing the size of required equipment. Experimental results confirmed that fluorapatite remains stable up to 900 °C and begins decomposing at higher temperatures, aligning closely with thermodynamic predictions. The subsequent smelting step, conducted with carbon as the reducing agent and silica as the fluxing agent, enabled over 95 % recovery of gaseous phosphorus at 1500 °C under optimal conditions.

Thermodynamic and experimental findings demonstrated that higher-grade phosphate ores necessitate higher operating temperatures for smelting. Optimal temperature ranges for thermal treatment and smelting of low-to high-grade phosphate ores were determined to be 800–1100 °C and 1300–1600 °C, respectively. Heavy metals such as cadmium, arsenic, and lead were fully removed during thermal treatment, while chromium, uranium, and vanadium predominantly remained in the slag phase during smelting. Zinc was the only heavy metal likely to co-mingle with gaseous phosphorus in the proposed process. The results validate the importance of fluxing and reducing agents in optimizing phosphorus recovery and highlight the potential for sustainable high-temperature processes. The influence of temperature, fluxing agents, and gaseous reactants on phosphorus recovery is thoroughly discussed, providing critical insights for process optimization.