<p>The selective recovery of rhenium (Re) from molybdenum-rich (Mo) hydrometallurgical solutions is a persistent challenge, hindered by the chemical similarity of the two elements and the poor performance of conventional extraction systems. This study elucidates a highly efficient separation strategy using the tertiary amine extractant N235, uniquely enabled by a synergistic phosphoric–sulfuric mixed-acid medium. We reveal a novel dual-pathway separation mechanism termed “acidity regulation and ion competition.” Specifically, sulfuric acid modulates the solution acidity to promote the dissociation of extractable molybdate anions (PMo₁₂O₄₀³⁻) into non-extractable MoO₂²⁺. Concurrently, phosphoric acid introduces a high concentration of competitive phosphate anions that saturate the extractant’s active sites, effectively suppressing the co-extraction of any residual anionic Mo species. This synergistic effect, corroborated by FTIR and DFT calculations, leads to exceptional selectivity. Under optimized conditions, a single-stage Re extraction of 98.6% was achieved with only 1.4% Mo co-extraction, yielding an outstanding separation factor (<i>β</i>_Re/Mo) of 4183. Furthermore, the loaded Re was efficiently stripped (&gt;98.2%) using 1 mol/L aqueous ammonia, and the organic system demonstrated excellent stability, maintaining over 96.3% extraction efficiency after six cycles. This work presents not only a robust and industrially viable process but also a new mechanistic paradigm for separating chemically analogous metals by synergistically manipulating solution speciation and competitive equilibria.</p>