1、英文原文A review of techniques for measurement of Contact angles and their applicabilityon mineral surfacesT.T. Chau CSIRO Minerals, Box 312 Clayton South, Vic. 3169, AustraliaAbstract. Knowledge of the wetting characteristic of mineral surfaces is paramount in enhancing the efficiency of separation of
2、valuable minerals from gangue using froth flotation. The contact angle value is a useful indi-cator providing the hydrophobic characteristic of the solid mineral surfaces due to a close relationship between this parameter and the floatability of minerals.In this paper, techniques for contact angle m
3、easurements and their applicability on mineral surfaces are reviewed. Two main groups of techniques for contact angle measurements are available; one group is applicable to flat and smooth surfaces while the other one has been especially developed for non-ideal surfaces or particles. Capillary penet
4、ration methods have been found to be more applicable than the other methods cited in measuring contact angles on real mineral surfaces. The major challenge with this tech-nique is the modification required to overcome the difficulties in the experimental packing technique needed, and more importantl
5、y, to obtain the receding contact angle values. The coupling of accurate con-tact angle measurements with real (batch) flotation data would seem to be area which has had limited attention.Key words. Contact angle Hydrophobicity Froth flotation1. IntroductionIn mineral processing, after grinding the
6、ore to liberate the min-erals, flotation is widely used to quickly and efficiently separate valuable minerals from the gangue minerals based on the differ-ences in their natural or induced hydrophobicity. Hydrophobic mineral particles are more readily attached to air bubbles and floated to the top o
7、f the pulp, whereas the hydrophilic gangue are not and report to the tailing.Overall, the flotation process can be divided into three major sub-processes; particlebubble collision, adhesion of the mineral particles to the air bubble, and detachment. The whole process is complicated further by the ad
8、dition of numerous reagents to the pulp to control surface properties of particles and the pulp chemis-try. The primary requisite for flotation is the replacement of water at the mineral surface by an air bubble and this can be quantified by a receding contact angle value. It is clear that a fundame
9、ntal under-standing of surface chemistry and wettability plays a crucial role in controlling the bubble/mineral adhesion sub-process ( Wark,1984). However, there is a gap in this area which requires further investigation to make improvements to the flotation process. Seri-ous efforts based on differ
10、ent approaches, including modeling, the-oretical and experimental studies are being conducted to bridge this gap. At CSIRO, a computational fluid dynamics (CFD) model is cur-rently being developed for mechanically stirred flotation cells where contact angle is one of a number of very important input
11、 parameters,that affects the accuracy and applicability of the model ( Koh and Schwarz, 2003, 2006). The success of this model may offer significant cost savings in modifications to existing equipment and operations to improve flotation performance. Therefore, achieving realistic con-tact angle valu
12、es for real mineral samples and precisely quantifying the impact of various factors on these values is important.The contact angle is a useful indicator in providing data on the wetting characteristic of solid mineral surfaces due to the close relationship between the contact angle and the floatabil
13、ity of min-erals. Over the years, many different techniques have been devel-oped for the measurements of contact angles. However, controversy still reigns in the literature on the accuracy and quality of the data reported and its suitability for use in the Young equa-tion, as discussed later. For re
14、al mineral systems, only a few of the available techniques can offer precise, meaningful and realistic contact angle values without unreasonable requirements and/or assumptions.This paper is aimed at reviewing available contact angle mea-surement techniques, especially those that are applicable to m
15、in-eral surfaces, accessing their pros and cons, and identifying possible methodologies for improvement and adaptation to real mineral surfaces to gain further understanding on their practical application in froth flotation. Details of most of the major contact angle measurement techniques and their
16、 experimental set-ups have been described by Adamson and Gast (1997), Hunter (2001), Ralston and Newcombe (1992) and Kwok and Neumann (1999). The methods can be generally divided into two main groups; one group is applicable to flat and smooth surfaces while the other one can be used for non-ideal surfaces or particles, which is arguably more relevant for real mineral surfaces. An up-to-date critical review of the proposed techniques is presented here.2. Background
