Hallimond tube flotation of scheelite and calcite with amines

Abstract

Hallimond tube flotation experiments have been carried out on the two calcium minerals scheelite and calcite using dodecylammonium chloride as collector. The main variables studied were the calcium ion concentration and the pH. In the case of scheelite, addition of calcium chloride markedly lowered the flotation recovery. Recovery was also lowered when the pH was reduced below about 10. Since it is known that the zeta potential of scheelite is almost independent of pH this confirms that co-adsorption of un-ionized amine is necessary for good flotation. Other un-ionized long-chain molecules can replace the amine; thus it was shown that excellent flotation can be obtained event at about pH 7 by adding dodecanol together with dodecylammonium chloride. With the completely ionic trimethyldodecylammonium chloride recoveries were poor and were independent of pH. In the case of calcite, calcium chloride had no immediate effect on flotation recovery, but at low collector concentrations marked depression occurred after many hours standing in the presence of calcium ions. The effect of pH on flotation of calcite was anomalous and there appear to be two pH regions in which recoveries are high. The results are discussed and attention is drawn to the need for more thorough studies of the calcium carbonate/water interface.