Tommi Rinne1, Mohazzam Saeed1, Rodrigo Serna Guerrero1,* 1 Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, 02150 Espoo, Finland; This email address is being protected from spambots. You need JavaScript enabled to view it. (T.R.);
* Correspondence: This email address is being protected from spambots. You need JavaScript enabled to view it. (R.S.)
Abstract: This research article studies selective flocculation as a means for entrainment prevention in flotation of analytically pure electrode mixtures of LiCoO2 (LCO) and graphite. Furthermore, scanning electron microscopy (SEM) is presented as a novel method for characterizing floc structure and morphology, and to determine the degree of selectivity in a process that applies selective flocculation as a conditioning stage for froth flotation. The results of the flotation experiments suggested that a branched, medium cationic polyacrylamide flocculant can be used to selectively aggregate LCO from mixtures with graphite when the pH of the pulp is maintained in the slightly acidic region of 5-6. Selective flocculation was observed to increase the grade of the recovered graphite concentrate from 99.3% to 99.5%. Proper pH control before and during the experiment allowed for the kinetics of the separation to not be influenced negatively by flocculation, which had been reported in earlier experimental campaigns. Furthermore, SEM was shown to provide visual proof of flocculated particles, even in dried froth samples. Under optimal flocculant concentration of 10 g/t, only a few flocs, consisting of ultrafine LCO particles only, were detected in the froth concentrate, which was evidence of a high degree of selectivity in flocculation. High flocculant concentration (50 g/t) was observed to result in multiple flocculated LCO particles within the froth. With the high flocculant concentration, the LCO flocs were observed to involve coarse particle in addition to fine particles, which could explain the drop in the selectivity of flocculation. The results suggest that selective flocculation could be a viable method for improving the separation efficiency of graphite from Li-ion battery waste, and that SEM can be applied for determining the selectivity in combined flocculation-flotation processes.