Controlling clay behaviour in suspension: developing a new paradigm for the minerals industry

© 2011 Dr. Josephine LimClays, which are often associated with mineral deposits, can be the source of significant problems in mineral processing operations. Their presence as impurities in low grade ores can lead to issues such as high pumping energy, high water consumption and large volume of tailings. Current strategies for dealing with clay related issues in mineral processing are all end-of-pipe in nature, in the sense that they all attempt to solve the problems well after they have been created through clay dispersion. However, the effectiveness of such strategies will always be limited due to the physical and chemical nature of clays. The purpose of this study is to develop a new paradigm for the minerals industry to control clay behaviour in suspensions using a start-of-pipe, or up front strategy that reduces the level of dispersion and break-up of the clays throughout the process. Through such a strategy, the occurrence of clay-associated problems will be predicted and moderated at the front end of a processing plant. This could result in significant improvements in dewaterability over the current end-of-pipe practice. The investigation of the start-of-pipe strategy for minimising in process clay break-up, referred to as controlled dispersion, was conducted on two clay minerals that are commonly associated in mineral ore bodies: kaolinite (non-swelling clay) and montmorillonite (swelling clay). In both cases, the focus was on controlling the dispersion and break-up of the clays during initial hydration, but due to differences in their physical and chemical properties, different strategies were investigated for each clay mineral subgroup. For the swelling clay minerals, the investigation was focused on as-mined Volclay bentonite swelling control through monovalent (Na+) and divalent (Ca2+) ion exchange and double layer compression. For the non-swelling clay minerals, the investigation was focused on the implementation of cementation via aluminium hydroxide precipitation on as-mined Skardon River kaolin. The outcomes from the investigation demonstrated that effective dispersion control could be achieved with the application of different controlled dispersion strategies. The resultant quantitative improvements in the physical properties of the clays, such as their dewaterability, were in excess of one order of magnitude in many cases. The benefits of the strategy to a mineral processing operation were illustrated via model simulations of the operation of an arbitrary steady state thickener. With the implementation of the controlled dispersion strategy, improvements were observed in either throughput or required equipment size in excess of one order of magnitude. Further investigations were then conducted on mixed clay mineral systems to illustrate the additive nature of the dispersion control strategies. The results highlighted the effectiveness of each controlled dispersion strategy in controlling the dispersion of the respective clay minerals, and also highlighted the importance of adequate clay mineralogical data for the processing plant feed to allow continuous adjustment and optimisation of the controlled dispersion strategy for systems with a clay composition that varies. For this reason, the potential use of Quantitative Scanning Electron Microscope system (QEMSCAN) technology as a clay mineral characterisation tool was investigated. However, due to its limitations in quantifying different clay minerals, the existing QEMSCAN technology needed development by customising the existing sample preparation method for clay-rich samples and updating the Species Identification Protocol (SIP) with the mineral database from a number of swelling and non-swelling clays. As a validation study, the QEMSCAN measurements of a range of clay-spiked samples were compared with the analysis from X-ray Diffraction. In general, the results demonstrated the potential for use of QEMSCAN for providing basic clay mineralogical data. However, further work needs to be completed to improve and quantify the accuracy of the results