Colloids and Surfaces A: Physicochem. Eng. Aspects 398 (2012) 32–36 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journa l h omepa g e: www.elsevier.com/locate/colsurfa Critical oil–liquid interfacial tension for some oil-assisted fine particle processing methods S. Duzyol a,∗ , A. Ozkan a , M. Yekeler b a Department of Mining Engineering, Selcuk University, 42075 Konya, Turkey b Department of Mining Engineering, Cumhuriyet University, 58140 Sivas, Turkey a r t i c l e i n f o Article history: Received 29 November 2011 Received in revised form 10 February 2012 Accepted 12 February 2012 Available online 17 February 2012 Keywords: Oil–liquid interfacial tension Oil agglomeration Liquid–liquid extraction a b s t r a c t This paper presents that oil–liquid interfacial tension ( OL ) value significantly affects the oil agglom- eration and liquid–liquid extraction processes as oil-assisted methods in fine particle processing. The decrease in the oil–liquid interfacial tension leads to the decreases in the recoveries of minerals in both oil agglomeration and liquid–liquid extraction techniques. Eventually, these oil-assisted methods do not take place below a particular value of oil–liquid interfacial tension. The oil–liquid interfacial tension value at which oil agglomeration does not occur was defined as ‘critical oil–liquid interfacial tension for oil agglomeration,  c–OL–a ’ and at which liquid–liquid extraction does not take place was also defined as ‘critical oil–liquid interfacial tension for liquid–liquid extraction,  c–OL–e ’. Consequently, the oil–liquid interfacial tension of the medium for successful processes of oil agglomeration and liquid–liquid extrac- tion of a mineral must be higher than the related critical interfacial tension value. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Fine particles produced during grinding process in mineral pro- cessing operations decrease the efficiency of the concentration processes. Therefore, there is considerable interest in develop- ing a process that could successfully handle such fine particles. Oil agglomeration and liquid–liquid extraction are important sep- aration techniques among oil-assisted fine particle processing processes [1]. In the oil agglomeration technique, hydrophobic par- ticles in aqueous suspensions are aggregated by oil droplets since oil preferentially wets the hydrophobic surfaces. Solid particles, therefore, can be bridged by the second liquid which is immiscible with the medium in which the process takes place [1,2]. In the case of liquid–liquid extraction process, large amounts of organic and aqueous phases are contacted and the particles, depending on their hydrophobicity, transfer either to the aqueous or organic phases. Both processes are only possible when the treated particles are suf- ficiently hydrophobic so that they are selectively wetted in water by oil [1,3]. Wetting of solid surfaces by liquids has many practical appli- cations and consequently has been an important area of both applied and basic research for many years. The wettability prop- erties of solids or minerals are assessed quantitatively by a number of experimental and empirical techniques. ‘The critical surface ten- sion of wetting ( c )’ is one of these quantifying parameters to ∗ Corresponding author. Tel.: +90 332 2232043; fax: +90 332 2410635. E-mail address: selmad@selcuk.edu.tr (S. Duzyol). achieve selectivity in surface chemistry processes such as flotation, shear flocculation, oil agglomeration, liquid–liquid extraction, dust abatement and solid–liquid separation [4,5]. Shafrin and Zisman [6] found that the contact angle () of a sessile liquid drop on a solid sur- face decreases in tandem with decrease of the air–liquid interfacial tension. Thereafter, Yarar and Kaoma [7] reported that the flota- tion recovery of minerals decreases as decrease of the air–liquid interfacial tension of the liquids used as flotation medium. Sim- ilar to the flotation behavior of minerals, the shear flocculation, oil agglomeration and liquid–liquid extraction recoveries of miner- als also decrease with decreasing the air–liquid interfacial tension. Eventually, while the flotation and shear flocculation of minerals do not occur at the air–liquid interfacial tensions below ‘the criti- cal surface tension of wetting ( c )’ value of the mineral [7,8], the oil agglomeration and liquid–liquid extraction processes of minerals do not take place at the air–liquid interfacial tensions lower than ‘the critical solution surface tension ( c–a ) for oil agglomeration’ and ‘the critical solution surface tension ( c–e ) for liquid–liquid extraction’, respectively. Also, it has been reported that the  c–a and the  c–e parameters are essentially the same, which are slightly higher than the  c value of the mineral [9,10]. The effect of air–liquid interfacial tension on flotation, shear flocculation, oil agglomeration and liquid–liquid extraction pro- cesses has been largely investigated previously as stated above. It is important to understand the interfacial phenomena of the three-phase system composed of oil, water and solids and to clar- ify the criteria of surface properties for successful operation of the oil-assisted separation methods such as emulsion flotation, oil agglomeration and liquid–liquid extraction [11]. However, the 0927-7757/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2012.02.005