Quantitative assessment of hydrophobic agglomeration performance X.Q. Wu a, * , A.J. Monhemius b, * , R.J. Gochin b a School of Resource Processing and Bio-engineering, Central South University, Changsha 410083, Hunan, China b Department of Earth Science and Engineering, Royal School of Mines, Imperial College, SW7 2BP London, UK Received 15 July 2004; accepted 9 September 2004 Abstract The process of agglomeration is quantitatively described by the use of two factors: (i) the hydrophobic compatibility between the solid and the liquid, and (ii) an agglomeration coefficient. If in an agglomeration system, the gap between the hydrophobicities of the agglomerants (i.e. the solid and the liquid) exceeds certain tolerances, it is difficult for the agglomeration process to proceed prop- erly, especially to produce appropriately sized, dense, agglomerates. By the use of certain organic surfactants, it is possible to adjust agglomerant compatibilities and make the agglomeration system work well. This promotion action of surfactants is explained in terms of the interfacial interactions and the immersion energy of the system. In addition, the agglomeration efficiency of different agglomerants can be evaluated by the Ôagglomeration coefficientÕ, which is measured by the capillary rise method and reflects the physical properties of the liquid and the mutual interactions between the solids and the liquid. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Agglomeration; Coal; Fine particle processing 1. Introduction Oil agglomeration is a process in which oil-solid agglomerates are formed by mixing oil with hydropho- bic solid materials. The main purpose of oil agglomera- tion is to selectively separate fine coal from coal shale slimes (Szymocha, 2003). In recent years, however, the oil agglomeration process has been used directly to re- cover gold particles, and the dense oil-carbon agglomer- ates formed by oil agglomeration have been used as a carrier or absorbent to recover gold from gold-bearing ores (House et al., 1988; Calvez et al., 1998). It is this lat- ter application of oil agglomeration that is the main focus of this paper. Specifically, the paper is primarily concerned with the quantitative assessment of the oil agglomeration process on the basis of the surface prop- erties of the liquid and solid agglomerants. The solid materials most commonly used for agglom- eration are various types of coal. Generally speaking, anthracite and bituminous coals respond better than lig- nite (Mehrotra et al., 1983). Furthermore, the moisture content, the porosity and the compositional parameters (carbon content, hydrogen content, oxygen content, atomic ratio of hydrogen/carbon, atomic ratio of oxygen/carbon) of coal are among the factors that affect the agglomeration response (Hatten, 1982; Moxon et al., 1987; Labuschagne et al., 1988). Labuschagne et al. (1988) proved that the moisture content of coal corre- lated more closely with its agglomeration response than the compositional parameters. Oil is preferentially ab- sorbed into the coal pores instead of spreading over the surface to form a film, and this results in the loss of collecting or bridging power. Being more porous, the coal surface is thus less easily covered by the oil (Moxon et al., 1987). 0892-6875/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2004.09.005 * Corresponding authors. Tel.: +44 207 594 7329; fax: +44 207 594 7444. E-mail addresses: xiqingwu@hotmail.com (X.Q. Wu), j.monhemius@imperial.ac.uk (A.J. Monhemius). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 18 (2005) 567–573