The effect of phyllosilicate mineralogy and surface charge on the rheology of mineral slurries

Includes abstract.Includes bibliographical references.Phyllosilicate minerals exist as common gangue components in many low grade ores. Often broadly classified as ‘clays’, this group of minerals is closely associated with several processing issues. Despite many good studies on the physico-chemical properties of phyllosilicates, there still remains a poor understanding of their suspension flow behaviour. The primary objective of this thesis was to characterise the colloidal behaviour of three commonly occurring phyllosilicates, namely muscovite, vermiculite and chrysotile in terms of their surface charge, mineralogical and resultant rheological properties. The thesis was initiated in order to gain a better understanding of the flow behaviour of these minerals within well-defined model mineral systems, with a longer term view to understanding their impact in complex mineral systems found in mineral processing circuits

Characterisation of kaolinite colloidal and flow behaviour via crystallinity measurements

This study evaluates the possibility of predicting colloidal and flow behaviour of kaolinite suspensions by measuring kaolinite crystallinity. The Hinckley index of different samples was calculated from XRD spectra as an indicator of the crystallinity. Kaolinite samples with a high Hinckley index showed a defined platy morphology with smooth surfaces of low surface area, whilst progressively roughened basal planes with prevalent broken edges were observed in kaolinite samples of lower Hinckley indices. Despite similarity in the elemental composition, the kaolinite samples present different surface charge properties, likely due to variations in exposed pH dependent edge sites. Poorly crystallised kaolinite samples were characterised by higher yield stresses and viscosities. This study highlights the importance of crystallinity characterisation towards predicting colloidal behaviour and flow characteristics of kaolinite suspensions

Behaviour of swelling clays versus non-swelling clays in flotation

The deleterious effects of clays on flotation performance are widely acknowledged but the mechanisms involved are not clearly established. Moreover, the concentrations beyond which clay minerals become problematic are not clearly defined. One major parameter is the difference between swelling and non-swelling clays which is evaluated in this study. The ore slurry pulp rheology and froth stability were monitored in the absence and presence of different clay minerals. It was found that swelling clays can adversely affect the flotation performance mainly via adsorbing water which changes the rheology and froth stability, reducing both flotation grade and recovery. Non-swelling clays had a lower effect on the rheology. Kaolinite increases the froth stability and reduces the flotation grade but illite showed the least effect on the flotation performance in this study. The potential mechanisms and critical concentrations are discussed

Behavior of talc and mica in copper ore flotation

Talc and mica are major gangue minerals in many base metal ores including sulfide ores. Talc is a naturally hydrophobic mineral, and therefore it is easily floatable. There have been many studies to overcome this problem, and depress talc with various reagents. In this study the flotation of a copper ore in the presence of talc and muscovite was studied. It was found that talc can affect copper flotation mainly via froth phase. The copper grade and recovery were affected in the presence of only 7% talc. On the other hand, muscovite influenced the pulp phase via affecting the pulp rheology. The copper flotation grade was reduced in the presence of high amount (30%) of muscovite due to the entrainment, but its effect on the copper recovery was negligible

Characterising the deleterious effect of phyllosilicate minerals on the copper flotation via froth stability analysis

The effects of phyllosilicate minerals on the flotation performance and froth stability of a copper ore was investigated. It was found that various phyllosilicate minerals affect the copper recovery differently however they all caused the flotation grade to be reduced. The effect of different phyllosilicate minerals on the froth stability followed the order of talc » montmorillonite > muscovite > kaolinite > illite. The results demonstrated that there could be a relationship between the deleterious effect of phyllosilicate minerals on the flotation and froth stability. Talc and montmorillonite have both shown the highest effect on the flotation recovery and grade as well as froth stability. On the other hand, illite has the least effect on the both flotation performance and froth stability. Kaolinite and muscovite also affected the copper flotation grade (but not the recovery) while they also affected the froth stability. Therefore it is possible to control the flotation performance when phyllosilicate minerals are present via monitoring and controlling froth stability which needs to be investigated further

A preliminary rheological classification of phyllosilicate group minerals.

With the increased exposure to progressively complex ores, there is growing concern over the effects of phyllosilicate gangue minerals. These minerals present challenges during ore beneficiation, with issuessuch as reduced flotation performance and complex tailings treatment arising. Often broadly classified as ‘clays’, the understanding of the distinct behaviour of phyllosilicates remains poor. This work focusses on talc, illite and kaolinite, and forms part of an ongoing study which aims at investigating the entire phyllosilicate group, categorised as serpentine, micas; talc/pyrophillite, kaolinites, illites, smectites and vermiculite. Using pure minerals belonging to each phyllosilicate type, a comprehensive surface charge and rheological analysis was conducted, incorporating their charge anisotropy and non-spherical morphology.The mineralogy was discussed, based on pre-existing knowledge of the minerals. Talc, kaolinite and illite suspensions are characterised by high yield stresses and low viscosities, with differences in their behaviour attributed to variations in charge anisotropy, aspect ratio and surface morphology. A comparison with other phyllosilicates showed that muscovite (mica) results in the least rheologically complex suspensions, while the fibrous nature of chrysotile (serpentine) leads to suspensions with the highest yield stresses and viscosities. The other minerals demonstrate intermediate rheological behaviour. Such a classification may be foundational to geometallurgical advances which can enable process performance predictions based on mineralogy