Adsorption of guar gum and CMC on pyrite O. Bicak a, * , Z. Ekmekci a , D.J. Bradshaw b , P.J. Harris b a Hacettepe University, Mining Engineering Department, 06800 Beytepe, Ankara, Turkey b Centre for Mineral Research, University of Cape Town, Cape Town, South Africa Received 13 December 2006; accepted 19 March 2007 Available online 9 May 2007 Abstract The depression of pyrite in sulfide flotation by two types of polysaccharides, CMC and guar, was investigated using micro-flotation tests, zeta potential measurements and adsorption tests. Environmentally and from an occupational safety standpoint – this would be a better processing option than cyanide. The range of variables tested included molecular weight of guar, degree of substitution of CMC, pH and the concentration of calcium ions in the flotation process water. The guar gums depressed pyrite considerably even at low dos- ages. An optimum dosage of 10 ppm was recommended. The CMC’s were not as effective as the guar gums, and required much higher dosages to achieve pyrite depression. Within the range of CMC’s tested, lower degree of substitution was more effective than high degree of substitution. This was presumably due to lower electrostatic repulsion between the negatively charged CMC and pyrite. When calcium ions were introduced with CMC’s, the adsorption of the CMC was considerably enhanced. No such effect was observed for guar gums. Both CMC and guar gums demonstrated Langmuirian behavior in their adsorption isotherms. Two different adsorption mechanisms were displayed. The guar gum adsorption was attributed to hydrogen bonding and Bronsted acid–base interaction. The CMC was considered to occur through electrostatic interaction in the presence of calcium ions, and Bronsted acid–base interaction depending on pH. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Sulfide ores; Flotation depressants; Polysaccharides; Adsorption 1. Introduction Pyrite is the most widespread and abundant of naturally occurring metal sulfides. It is commonly present in base metal sulfide bearing ores and frequently appears in coal as a major source of sulfur in coal. Pyrite lowers the quality of base metal concentrates and increases the amount of sul- fur compounds produced in the base metal extraction pro- cesses. Therefore, depression of pyrite is essential in the concentration of base metal sulfides by flotation. This can be achieved by floating in alkaline solutions using highly selective inorganic modifiers such as cyanides, sulfites, ferro-cyanides, etc. However, the use of inorganic depres- sants have raised concerns on environmental grounds. Hence, natural, bio-degradable, non-toxic agents such as polysaccharides are worth investigating as alternative selec- tive depressants. Kydros et al. (1994) have reported separa- tion of pyrite/sphalerite mixtures with copper sulphate, ethyl xanthate and white dextrin. Valdivieso et al. (2004) showed that dextrin can be as an effective depressant of pyrite as cyanide. Polysaccharides are a promising class of strong depres- sants that could replace the highly toxic inorganic modifi- ers in the differential flotation of sulfide minerals. However, although they have been reported as selective depressants in the differential flotation of sulfide minerals (Laskowski et al., 2000) a general lack of understanding of the interaction mechanism between the polysaccharides and sulfide mineral surfaces hinders the development in this area. It has been reported that these polymers adsorb through interactions with metal-hydroxy species on the mineral surfaces (Laskowski and Liu, 1999a,b) but other mechanisms such as hydrogen bonding, hydrophobic 0892-6875/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2007.03.002 * Corresponding author. E-mail address: obicak@hacettepe.edu.tr (O. Bicak). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 20 (2007) 996–1002