A novel switchable collector for selective flotation of fine copper oxide from silica

A novel pseudo-Gemini collector (PGC) featuring pH-responsive collecting power and enhanced selectivity is developed for flotation recovery of fine copper oxides from silica. The switchable PGC is formed through ionic pairing between protonated triethylenetetramine (TETA) and deprotonated oleic acid (OA) and is referred to as T-OA. The formation of T-OA was characterized by determining its critical micelle concentration of 0.6 mM at pH 10, which is much lower than that of 2.5 mM for its counterpart of OA, demonstrating a stronger surface activity of the novel T-OA collector for hemimicelle formation. Micro-flotation results showed a CuO recovery of over 90% at T-OA concentrations as low as 0.01 mM and pH 10, at which the collector exists in pseudo-Gemini form. Adjusting the flotation pH to 5 switched T-OA to monomeric form of OA with a lower surface activity but a higher selectivity which was further improved by removal of activating ions from silica by TETA. Introducing T-OA of higher collecting power in the rougher stage and then switching to a lower collecting power form of higher selectivity in the subsequent cleaner stage enhanced the flotation separation of fine CuO from silica. Zeta potential measurements indicated adsorption of T-OA on copper oxide at pH 5 and 10 with the hydrophobicity of copper oxide being stronger at alkaline conditions than that at acidic conditions as determined by contact angle measurement. The switchability of T-OA activity on CuO surfaces was illustrated by contact angle and in situ particle size distribution measurements. The reversible adsorption of T-OA on copper oxide at pH 10 was shown by QCM-D results. The results in the current study using switchable T-OA provide a clear direction for design of switchable collectors to achieve the control of the collecting performance and selectivity during the flotation processes, enhanced overall flotation performance.