The effects of Ca(II) and Mg(II) ions on the flotation of spodumene using sodium oleate (NaOL) as the collector were investigated by micro-flotation tests, zeta-potential measurements, absorption measurements, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses. The micro-flotation results indicated that the pH value has a significant influence on the activation of spodumene minerals by Ca(II) and Mg(II) ions. Good floatability of spodumene was obtained with Ca(II) and Mg(II) ions at a pH of 12.5 and 10.0, respectively. In strongly alkaline solutions, Ca(II) and Mg(II) ions'readily form hydroxy complexes (CaOH(I) and MgOH(I)) and precipitates (Ca(OH)(2) and Mg(OH)(2)). FT-IR and XPS analyses revealed that the hydroxy complexes and the precipitates adsorbed onto the spodumene surface. These species contributed to the formation of oleate complexes and thus increased the amount of collector adsorption and the floatability of spodumene. (C) 2015 Elsevier Ltd. All rights reserved.