Marek Zbik

Nanomorphology of kaolinites; comparative SEM and AFM studies

Nanomorphological structure of well-crystallized Georgia and poorly crystallized North Queensland kaolinite particles have been compared using field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM). In general, there is good agreement in information from the 2 very different imaging techniques. AFM gives more detailed information on step and ledge dimensions, microvalleys and crystallographic orientation of irregularities on basal planes and edges of the crystallites. There are major differences in nanomorphology and surface structure between the 2 kaolin samples with the Georgia kaolin showing 200–500-nm, relatively flat basal planes with some cascade-like step growth 50–100 nm wide. The edges, apparently flat and right-angled in SEM images, appear beveled in AFM images due to artifacts from the aspect ratio of the AFM tip. The North Queensland kaolinite has much more complex surface structure with anhedral crystallites attached to larger particles, high density of steps and nm-scale irregularities (often crystallographically directed). The additional step edge site contribution from the attached crystallites is estimated as a minimum of 6%, giving a total edge contribution above 30% of the kaolinite total surface area. These structures will generate a substantial pH-dependent charge across the surfaces of the North Queensland kaolinite platelets. An idealized, uniform, pH-independent, negatively charged basal plane cannot be assumed from these structures. There is also some evidence, from both SEM and AFM images, of curvature in the thinner, poorly ordered structures of the North Queensland kaolinite particles.

Kaolinite flocculation structure

Effective flocculation and dewatering of mineral processing streams containing colloidal clays has become increasingly urgent. Release of water from slurries in tailings streams and dam beds for recycle water consumption, is usually slow and incomplete. To achieve fast settling and minimization of retained water, individual particles need to be bound, in the initial stages of thickening, into large, high-density aggregates, which may sediment more rapidly with lower intra-aggregate water content. Quantitative cryo-SEM image analysis shows that the structure of aggregates formed before flocculant addition has a determinative effect on these outcomes. Without flocculant addition, 3 stages occur in the mechanism of primary dewatering of kaolinite at pH 8: initially, the dispersed structures already show edge-edge (EE) and edge-face (EF) inter-particle associations but these are open, loose and easily disrupted; in the hindered settling region, aggregates are in adherent, chain-like structures of EE and stairstep face-face (FF) associations; this network structure slowly partially rearranges from EE chains to more compact face-face (FF) contacts densifying the aggregates with increased settling rates. During settling, the sponge-like network structure with EE and FF string-like aggregates, limits dewatering because the steric effects in the resulting partially-gelled aggregate structures are dominant. With flocculant addition, the internal structure and networking of the pre-aggregates is largely preserved but they are rapidly and effectively bound together by the aggregate-bridging action of the flocculant. The effects of initial pH and Ca ion addition on these structures are also analyzed. Statistical analysis from cryo-SEM imaging shows that there is an inverse correlation of intra-aggregate porosity with Darcian inter-aggregate permeability whereas there is a strong positive correlation of Darcian permeability with settling and primary dewatering rate as a function of pH in suspension. Graphs of partial void contributions also suggest that it is not total porosity that dominates permeability in these systems but the abundance of larger intra-aggregate voids.

Birdwood kaolinite: a highly ordered kaolinite that is difficult to intercalate—an XRD, SEM and Raman spectroscopic study

The intercalation of a highly ordered kaolinite from Birdwood, South Australia, has been studied using a combination of electron microscopy, X-ray diffraction and Raman microscopy. Highly ordered kaolinites normally intercalate easily and to a high degree. The kaolinite under study was found to intercalate acetamide and formamide with difficulty and more than 18 days were required to achieve more than 20% intercalation. Further treatment did not improve the degree of intercalation past 60%. The difficulty of intercalation is attributed to the co-existence of two kaolinite phases, a highly ordered (with a Hinckley index>1.3) and a highly disordered kaolinite, the latter material appears to coat the highly ordered kaolinite thereby limiting the intercalation. The presence of two forms of silica and a dickite were identified in the sample using X-ray diffraction.

Dispersion of kaolinite and talc in aqueous solution: nano-morphology and nano-bubble entrapment

Abstract Nano-morphological structure of well-crystallised kaolinite, micronised talc and micronised talc ground in a ring mill has been compared using field emission scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kaolinite and ground talc dispersed in water immediately after shaking whereas the majority of the micronised talc remains at the air–water interface. AFM micrographs revealed more three-dimensional details of growth steps and attached colloid particles on basal planes of the crystallites than high resolution SEM micrographs. Two-dimensional ordered surface structure on the molecular level was measured by AFM. There are major differences in nano-morphology and surface structure between these three samples. The compact, blocky kaolinite crystals show large, relatively flat (

Influence of hydrocarbon contamination on clay soil microstructure

Abstract Microstructural (fabric, forces and composition) changes due to hydrocarbon contamination in a clayey soil (glacial till) were studied using scanning electron microscopy (microfabric analysis), atomic force microscopy (force measurement) and a sedimentation bench test (particle size measurements). Non-polluted and polluted glacial till from NE Poland (in the area of a fuel terminal) were used for the study. Electrostatic repulsive forces in the polluted samples were much lower than in non-polluted samples. In comparison with non-polluted samples, the polluted samples exhibited lower electric charge, attractive forces on approach and strong Adhesion on withdrawal. The results of the sedimentation tests indicate that clay particles form larger aggregates and settle out of the suspension rapidly in diesel oil. In non-polluted soil, the fabric is strongly aggregated - dense packing, dominating face-to-face and edge-to-edge types of contacts, clay film tightly adhering to the surface of larger grains and interparticle pores are more common. In polluted soil the clay matrix is less aggregated - loose packing, dominating edge-to-face types of contacts and inter-micro-aggregate pores are more frequent. Substantial differences were observed in the morphometric and geometrical parameters of the pore space. The polluted soil micro-fabric proved to be more isotropic and less oriented than in non-polluted soil. The polluted soil, in which electrostatic forces were suppressed by hydrocarbon interaction, displays more open porosity and larger voids than non-polluted soil, which is characterized by the occurrence of strong electrostatic interaction between the clay particles.

Micro-structure differences in kaolinite suspensions

SEM observations of the aqueous suspensions of kaolinite from Birdwood (South Australia) and Georgia (USA) show noticeable differences in number of physical behaviour which has been explained by different micro-structure constitution. Birdwood kaolinite dispersion gels are observed at very low solid loadings in comparison with Georgia KGa-1 kaolinite dispersions which remain fluid at higher solids loading. To explain this behaviour, the specific particle interactions of Birdwood kaolinite, different from interaction in Georgia kaolinite have been proposed. These interactions may be brought about by the presence of nano-bubbles on clay crystal edges and may force clay particles to aggregate by bubble coalescence. This explains the predominance of stair step edge-edge like (EE) contacts in suspension of Birdwood kaolinite. Such EE linked particles build long strings that form a spacious cell structure. Hydrocarbon contamination of colloidal kaolinite particles and low aspect ratio are discussed as possible explanations of this unusual behaviour of Birdwood kaolinite. In Georgia KGa-1 kaolinite dispersions instead of EE contact between platelets displayed in Birdwood kaolinite, most particles have edge-to-face (EF) contacts building a cardhouse structure. Such an arrangement is much less voluminous in comparison with the Birdwood kaolinite cellular honeycomb structure observed previously in smectite aqueous suspensions. Such structural characteristics of KGa-1 kaolinite particles enable higher solid volume fractions pulps to form before significantly networked gel consistency is attained.

Observation of gaseous films at solid–liquid interfaces: Removal by ultrasonic action

The critical role of dissolved gas nano-bubbles at solid surfaces in particle association, aggregation, adsorption and flotation has been recognised in the recent literature. The principles of mineral processing, fine particle separation, and water recovery depend upon changing the surface properties at the solid-liquid interface. It has been assumed that the solid surfaces are either in direct contact with the liquid or may have nano-bubbles attached only at hydrophobic surfaces. This paper shows that gaseous layers 50-100 nm thick can be attached surrounding high proportions of solid clay mineral surfaces restricting reagent access, producing buoyancy and aggregation. Ultrasonic treatment before flocculant addition effectively removes these gaseous layers as well as dispersed micro-bubbles. Re-aggregation after brief ultrasonication produces denser (less buoyant) flocs, demonstrated with cryo-SEM statistical analysis, giving more complete access of the flocculant to the aggregate surfaces. In the subsequent flocculant addition, the settling rates of the denser flocs can be increased up to 40%. If ultrasonic action is continued, the bridged flocs are disturbed with some redispersion of smaller flocs and individual platelets and consequent slower settling rates.

Discovery of Discrete Structured Bubbles within Lunar Regolith Impact Glasses

The unusual morphology and internal structure of bubbles within lunar regolith impact glasses have been studied using traditional scanning electron microscopy and the novel technique transmission X-ray microscopy (TXM), with 3D tomography reconstruction. Here, we show the previously unknown phenomenon of building a highly porous cellular structure within bubbles in glassy particles of the dust fraction of lunar regolith. Vesicles within studied lunar glasses are filled in with submicron-sized particles as shown in the presented micrograph. These particles consist of glass nano in size elements. What is shown in the TXM tomography reconstruction anaglyph demonstrates cellular-like, 3D structure where oblique probably glassy fine particles down to 100 nm in diameter build chains of sophisticated network. It also may be suggested that submicron and nano-sized grains present in lunar regolith are the result of particle liberation from broken glassy vesicles. This liberation takes place when regolith is exposed to constant impact pulverisation. Liberated particles are permanently enriching lunar soil in the finest soil constituent. This constituent presence in lunar regolith may be responsible for the unusual behaviour of lunar material. This unusual constituent of lunar regolith and its properties have to be better understood before our permanent lunar exploration begins.