In situ study of aggregate sizes formed in chalcopyrite-quartz mixture using temperature-responsive polymers

An interesting property of temperature-responsive polymers, such as poly(N-isopropylacrylamide) (PNIPAM), is the ability to behave as flocculants above a lower critical solution temperature (LCST). This study examines the aggregation of a chalcopyrite-quartz mixture using a sulfide-selective temperature-responsive polymer, P(NIPAM-co-ethyl xanthate methacrylate (EXMA)) in a continuously-sheared suspension, relative to polyacrylamide (PAM). The investigation was carried out in situ using imaging and Focused Beam Reflectance Measurement techniques to obtain real-time chord length distributions. While particle aggregates were observed in the presence of PNIPAM only upon heating above the LCST, P(NIPAM-co-EXMA) induced particle aggregation below the LCST, due to the attraction between the xanthate moiety and the sulfide surfaces. The largest aggregates were observed with P(NIPAM-co-EXMA) (1.5 MDa), followed by PNIPAM, PAM, and P(NIPAM-co-EXMA) (115 kDa). Particle aggregates formed with PAM did not exhibit further breakage under increasing shear to 1100 s⁻¹, while large-scale fragmentation was observed with the PNIPAM-based flocculants. Unlike PNIPAM, addition of P(NIPAM-co-EXMA) to suspension above the LCST was able to yield particle aggregation, attributed to the formation of charge-stabilised micelles. The influence of the shear rate on the size of the aggregates formed with P(NIPAM-co-EXMA) is unaffected by the polymer addition and measurement temperature below or above the LCST.