Effects of water chemistry on the flotation of pyrochlore and silicate minerals

Abstract

Flotation of pyrochlore and silicate minerals (albite, biotite, chlorite and microcline) in distilled water, Montreal tap water and plant recycle water from La Mine Niobec has been investigated. Pyrochlore recovery with a secondary amine type reagent is much lower in recycle water than in the other waters. Treatment with oxalic acid (to a pH of about 2) improves the recovery in recycled water. No significant improvement is observed when the pH is lowered by HCl. This suggests that the precipitation of Ca++ (as Ca oxalate) present in recycle waters leads to improved recovery. This is confirmed by treatment of the recycle water with a cationic exchange resin which resulted in excellent flotation of pyrochlore. Removal of Ca++ by precipitation with Na2CO3 did not improve flotation; it is shown that Na+ is equally detrimental to flotation.Electrokinetic measurements indicate that Ca++ and Mg++ cations strongly reduce the negative charge at the pyrochlore surface. This hinders adsorption of the cationic collector. A possible mechanism of collector action is discussed.Treatment of recycle water with active carbon removes the organic matter. This improves pyrochlore selectivity by reducing the flotation of silicate minerals.