This paper reports a study on the purification behavior of methyl isobutyl ketone (MIBK) for the major impurities of the phosphoric acid wet process (Ca2+, Mg2+, Al3+, Fe3+, SO42-, and F-). Distribution coefficients of phosphoric acid (PA) and impurities, as well as selectivity of MIBK for PA, have been studied as a function of the PA concentration (wt%) in the organic phase. Our results are compared to those obtained with other solvents (isoamyl alcohol, dibutyl ether, and dipropyl ether) described in the literature. MIBK seems to have the best selectivity far PA against SO42-, and it shows an intermediate behavior between those of isomyl alcohol and ethers with regard to metallic impurities.