Abstract
The Ba 2+ ion adsorption isotherms on β-MnO 2 were of the Langmuir type. The endothermic heat of adsorption (40 kJ mol −1) is ascribed to entropy contributions associated with the Na + Ba 2+ ion-exchange mechanism. The Ba 2+ ion adsorption density was higher at pH 10 than that at pH 7, due to the more negative surface charge at the higher pH. Ba 2+ ions were found to reverse the sign of the ζ potential of the MnO 2 particles. More oleate was adsorbed by β-MnO 2 in the presence of Ba 2+ ions than in their absence. The oleate adsorption isotherms on Ba 2+-activated MnO 2 were of the Freundlich type and indicated an exothermic process. Hallimond flotation recovery of Ba 2+-activated MnO 2 was higher at pH 10 than at pH 7, although less oleate was adsorbed at the higher pH. At pH 7, Mn 2+-activation led to higher recoveries than Ba 2+-activation. It seems that the attraction between the surface and the activator plays an important rôle in determining the flotation recovery.
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