n-octylphosphonic acid (OPA) was introduced as a novel collector for ilmenite flotation and its effectiveness was compared with the conventional chelating collector, benzohydroxamic acid (BHA). Micro-flotation tests demonstrated that OPA was a highly effective and selective collector for separating ilmenite from titanaugite over acidic conditions (optimal pH around 3), which was also supported by adsorption amount measurements. X-ray photoelectron spectroscopy (XPS) tests indicated that the chemisorption of OPA onto ilmenite surface was much stronger than that of BHA. Solution chemistry diagram analyses indicated that OPA could dissociate well at pH 3.0 and mostly exist in anion form. DFT calculations further confirmed that OPA was much easier to adsorb onto ilmenite surface with shorter bond length and lower adsorption energy in comparison with BHA. Therefore, OPA maintained good collecting ability and selectivity for ilmenite flotation in the strongly acidic pulp, providing valuable insights into new collector design and development.