The value and limitations of electrochemical measurements in flotation of precious metal ores Z. Ekmekc ¸i a, * , M.A. Buswell b , D.J. Bradshaw b , P.J. Harris b a Hacettepe University, Mining Engineering Department, 06532 Beytepe, Ankara, Turkey b Mineral Processing Research Unit, Department of Chemical Engineering, University of Cape Town, PO Rondebosch, Cape Town 7700, South Africa Received 4 December 2004; accepted 7 January 2005 Available online 25 May 2005 Abstract Electrochemicalmeasurementshavesuccessfullybeenusedtointerpretflotationbehaviourofsulphideoresastheirflotationper- formance is considerably affected by the oxidation state and amount of different minerals in the ore, the galvanic interactions between grinding media/sulphide minerals and sulphide minerals with different rest potentials, chemicals and dissolved ions in the pulp. However, although the Merensky ore obtained from Bushveld Igneous can be considered as a complex sulphide ore in terms of variety of the sulphide minerals, the total sulphide mineral content is less than 1%. Therefore, the usefulness of the elec- trochemicalmeasurementsinflotationofMerenskyorewasdiscussedbasedonthemineralpotentialmeasurementstakenfromthe experiments performed with different types of milling media in the presence and absence of copper sulphate. The results revealed thatitcouldbemisleadingtorelateflotationbehaviourofthesulphidemineralsinMerenskyoredirectlywiththeelectrodepoten- tials,presumablyduetopresenceofverylowcontentofsulphidemineralsandtheinfluenceofotherfactorssuchasfrothstability which changed depending on the type of milling media and copper sulphate addition. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Precious metal ores; Redox reactions; Grinding; Froth flotation 1. Introduction Inflotation,theseparationofvaluablemineralsfrom unwanted gangue is made on the basis of differences in mineral surface hydrophobicity. In sulphide flotation, thiolcollectorsareaddedtorenderthesulphidemineral surfaceshydrophobic.Thisisachievedbythecollector— mineral reactions resulting in the formation of hydro- phobic surface species such as elemental sulphur, a metal-deficient sulphur layer, metal–xanthate or dix- anthogenformationatthesurface.Thesereactionshave beenshowntobeelectrochemicalinnature(Toperi and Tolun,1969;Allisonetal.,1972;FinkelsteinandPoling, 1977;Woods,1984)andtheiroccurrenceisinfluencedby process conditions such as the amount of different sul- phide minerals, the oxidation state of the minerals and theirgalvanicinteractions,aswellaschemicalsanddis- solvedionspresentintheflotationpulp. It is therefore expected that it would be possible to optimize flotation performance, both bulk recovery and selectivity, by the control of the oxidation–reduc- tionorredoxpotential(E h )asmeasuredintheflotation pulp.However,ithasnotbeenpossibletogeneralizethe relationship between the electrochemical measurements inthepulp(suchas E h anddissolvedoxygenconcentra- tion(DO))andtheflotationbehaviourofsulphidemin- eralsfromdifferentdepositsduetothedifferencesinthe mineralogy and electrochemical reactivity of the sul- phide minerals (Labonte and Fich, 1988; Hintika and 0892-6875/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2005.01.026 * Corresponding author. Tel.: +90 312 297 7660; fax: +90 312 299 2155. E-mail address: zafir@hacettepe.edu.tr (Z. Ekmekc ¸i). Thisarticleisalsoavailableonlineat: www.elsevier.com/locate/mineng Minerals Engineering 18 (2005) 825–831