The oil agglomeration of quartz with sodium oleate in the presence of calcium and magnesium ions comprises three consecutive stages: adsorption of cations onto quartz surfaces, which leads to coagulation of the Suspension, shear flocculation with sodium oleate and finally, agglomeration of flocs by kerosene. The effects of pH and cation concentration on these stages were investigated and the results were presented comparatively. It was found that all the stages of oil agglomeration of quartz exhibited sharp dependences on pH and cation concentration. That is, these stages generally took place in the pH and concentration ranges in which hydroxy complexes of the cations existed in the Suspension. In the case of magnesium ion, the coagulation, shear flocculation and especially oil agglomeration of quartz improved after precipitation of hydroxide. These species of calcium and magnesium ions formed at high pH were adsorbed oil the negatively charged Surface of quartz, as a result Of which the adsorption of sodium oleate became possible and thus the shear floccuation of the particles was achieved. Thereafter, the hydrophobic quartz flocs could be agglomerated by kerosene as bridging liquid. The increase in the shear flocculation efficiency depending oil the increase of surface hydrophobicity enhanced the oil agglomeration of quartz with kerosene. The maximum recoveries for all the stages of the quartz were obtained in the presence of 10(-3) M magnesium and 5 x 10(-3) M calcium ions at pH 11. However, some differences in file behavior of shear flocculation and oil agglomeration of quartz suspension were observed above 10(-3) M concentration of magnesium ion. (C) 2008 Elsevier Inc. All rights reserved.