A series of flotation tests on coarse KCl particles in brine solution prepared from potash ore from the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil was carried out to determine the recovery of sylvite in the presence of high concentrations of Mg2+. The introduction of Mg2+ caused the precipitation of fine salt crystals that consist mostly of NaCl (90%+) but also some KCl. However, the introduction of Mg2+ also caused the nucleation of fine crystals of NaCl and KCl on the surface of the coarse KCl in the flotation feed. The nucleation of these fine surface crystals on the coarse KCl may have added to a (net) improvement in the recovery of the coarse KCl. However, a precipitate of fine NaCl with some KCl crystals, competed for collector and caused depression of the coarse KCl. When these precipitates were removed before collector addition, the collector subsequently adsorbed on the coarse KCl and the recovery of coarse KCl improved significantly. (C) 2007 Elsevier Ltd. All rights reserved.