| Summary: | In this paper, the beneficiation of rejected phosphate washing sludges (Ps) was investigated using acid leaching methods. Chemical analysis showed that these sludges are a low-grade ore (15.84% P<sub>2</sub>O<sub>5</sub>). The optimum milling parameters have helped to increase the P<sub>2</sub>O<sub>5</sub> grade to 18.51%. Then, the effects of three different organic acids (acetic, lactic, and citric acid), acid concentrations, reaction temperatures, reaction times, and solid concentrations on the beneficiation of P<sub>2</sub>O<sub>5</sub> were evaluated. Single-factor experiments indicate that with the optimal conditions: leaching for 60 min with an acetic acid concentration of 7%, a solid concentration of 25%, and a temperature of 40 °C, Ps could reach 30.1% P<sub>2</sub>O<sub>5</sub> with a CaO/P<sub>2</sub>O<sub>5</sub> ratio of 0.58. Taguchi experimental design, Pareto plot, desirability function, and Analysis of Covariance (ANCOVA) showed that the acid type has the most significant impact on the leaching and the optimized leaching conditions: 7% of acetic acid, a solid concentration of 30%, a reaction time of 100 min, and a temperature of 40 °C, helped to produce a Ps with 30.7% P<sub>2</sub>O<sub>5</sub>. The kinetic study showed that the leaching process was controlled by a chemical reaction, with an activation energy of 48.9 kJ/Mol, which confirms the chemical reaction’s control of the process.
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