Liquid–liquid extraction of phosphorus from sulfuric acid solution using benzyl dimethyl amine

This study addresses the liquid–liquid extraction behavior of phosphorus from a sulfuric acid solution using benzyl dimethyl amine (BDMA) in kerosene. The extraction equilibria investigated with varied BDMA concentrations could reveal the formation of\begindocument\overline 3\left \rmBDMA \right \cdot \left \rmH_3\rmP\rmO_4 \right \enddocumentcomplex in the organic phase. The thermodynamic properties determined at various temperatures indicated that the process was exothermic with a calculated enthalpy (\Delta H^ \ominus ) of −24.0 kJ·mol⁻¹. The organic-to-aqueous phase (O/A) volume ratio was varied to elucidate the quantitative extraction of phosphorus. The McCabe–Thiele diagram plotted for the extraction isotherm was validated for the requirement of three counter-current stages in the extraction at an O/A volume ratio of 2.0/3.5. The back-extraction of phosphorus from the loaded organic phase was quantitatively achieved by contacting 4.0 mol·L⁻¹ H₂SO₄ solution in three stages of counter-current contact at an O/A volume ratio of 3/2. This study can be applied to remove phosphorus from the sulfuric acid leach solutions of monazite processing, and many other solutions.