The dissolution of minerals provides elevated concentrations of alkaline earth metal ions such as calcium (Ca2+) in water which may have a significant influence on flotation performance. The effects of Ca2+ ions dissolved from calcite surfaces on the flotation performance of a monazite-calcite system have been investigated using micro-flotation tests followed by fundamental-collector adsorption studies. The results indicate that specially adsorbed CaOH+ via hydrogen bonding competed with hydroxamic acid for the phosphate-oxygen active sites on the monazite surface and decreased its hydrophobicity due to hydration. Electrostatically adsorbed CaOH+ on monazite increased the adsorption density of hydroxamic acid through a chelating interaction. At higher dosages of calcium and hydroxamic acid, bulk and surface precipitation of calcium-hydroxamate occurs in the monazite-calcium-hydroxamic acid system. (C) 2016 Elsevier Ltd. All rights reserved.