Partition of pyrite in aqueous biphase systems

The feasibility of extending the aqueous biphase extraction process to mine ral sulfides was investigated with pyrite (FeS2) as a model metal sulfide i n polyethylene glycol (PEG)-based biphase systems. The phase diagram for th e PEG-2000/Na2CO3/H2O system was determined; with increase in the PEG molec ular weight, the binodal curve shifted in the direction of lower polymer an d salt concentrations. The partitioning behavior of pyrite in PEG/Na2CO3/H2 O and PEG/Na2SO4/H2O systems was investigated and the effects of conditioni ng time, pH, and PEG molecular weight were also studied. Pyrite particles d istributed to the interface initially; but with increasing conditioning tim e, the particles transferred preferentially to the bottom salt-rich aqueous phase. Pyrite partition was also pH-dependent. When the pH was above 9, py rite transferred into the salt-rich phase; between pH 5 and 9, it preferred the interface; and below pH 5, pyrite went into the top polymer-rich phase . The above trends an rationalized in terms of the effects of conditioning time and pH on the surface oxidization of pyrite and how this, in turn, cha nges the relative concentrations of hydrophilic and hydrophobic sites on th e solid surface. (C) 2000 Elsevier Science B.V. All rights reserved.