Pyrite and pyrrhotite open circuit potentials study: Effects on flotation H. Moslemi a , P. Shamsi b,⇑ , F. Habashi c a University of Tehran, Iran b Islamic Azad University – Shahindezh Centre, Iran c Laval University, Canada article info Article history: Received 2 September 2009 Accepted 1 May 2011 Keywords: Mineral processing Froth flotation Oxidation Reduction pH control abstract In this research, effects of chloride & sulfate ions and pH changes on the open circuit potentials of pyrite, pyrrhotite and steel and also their reduction–oxidation processes were studied. These potentials were measured at different pH values in 3 electrolytes: distilled water, sodium chloride solution and sodium sulfate solution. A pair of electrodes including reference and operative electrodes was used for measure- ment and control of potentials. The results showed that with pH increasing, pyrite and pyrrhotite open circuit potentials decrease whereas under the same conditions the mentioned potential for steel rises. It was also observed that use of sodium chloride and sodium sulfate solutions as electrolyte decreases the open circuit potentials, because the presence of chloride and sulfate ions speeds up the oxidation– reduction process. Furthermore, the effect of the mentioned parameters on galvanic interactions between minerals and grinding media in grinding circuits, as well as galvanic interactions between the minerals in flotation process, mineral floatability and their collector adsorption have been discussed. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction It is more than five decades that electrochemistry mechanism has been used for justification of some phenomena in flotation operations (Woods, 1996) and electrochemical techniques were applied by a number of authors to the investigation of sulfide flo- tation systems, particularly during the late 1970s and the 1980s (Woods, 2003). Floatability of sulfide minerals depends on the potential differ- ence at the interface of minerals and solution; and their flotation is implemented by oxidation and reduction reactions. Pulp oxidation potential (Eh) controls the formation of surface species responsible for minerals flotation (Leppinen et al., 1995; Leja, 1982; Rao, 1971). Therefore we can obtain the flotation conditions of minerals by measurement of oxidation and reduction potentials (Marouf et al., 1986; Kocabag et al., 1990; Goktepe and Williams, 1995). It is well known that the chemical environment determines the success of the flotation process (Bradshaw et al., 2006) and control of the solution pH is one of the most widely applied methods for the modulation of mineral flotation (Janetski et al., 1977). Change of pH is a factor which affects oxidation–reduction reac- tions as well as open circuit potentials; therefore it influences the galvanic interactions between the minerals. As the Iranian mines are located in desert, the water used for mineral processing plants includes different compounds in solution. Sodium chloride and sodium sulfate are common compounds in these waters and their effect on the open circuit potentials is as significant as that of pH amount. This causes changes in the floatability of sulfide minerals. One of the most important separation stages in flotation circuits is the elimination of pyrite and pyrrhotite (abundant gangue min- erals for base metal sulfides) from other sulfide minerals. These minerals have very little economical value and are the main source of SO 2 (which causes corrosion in operational equipment during grinding), difficulty in selective flotation and hazardous effects on the environment. Galvanic interactions between grinding media and sulfide minerals (especially pyrite and pyrrhotite) are a com- mon and unavoidable phenomenon in minerals beneficiation. In this study effects of pH changes and presence of chloride and sulfate ions on open circuit potentials by two electrodes (reference and operational), in the laboratory tests (with carefully controlled conditions) were determined and the effects of these factors on oxidation–reduction reactions have been discussed. 2. Methods and materials Fig. 1 shows the circuit used for measurement of open circuit potentials. In this circuit, potential differences between mineral and metal electrodes in different electrolytes with regard to refer- ence electrode were determined by use of a digital multimeter (Hioki32 model). Potentials were read promptly after submerging the electrodes inside the solution and at 5 min intervals. This 0892-6875/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2011.05.001 ⇑ Corresponding author. Tel.: +98 912 437 2105. E-mail address: pourang_shamsi@yahoo.com (P. Shamsi). Minerals Engineering 24 (2011) 1038–1045 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng