Colloidal silica is used in many applications including catalysis, pharmaceuticals, and coatings. Although naturally formed silica materials are widely available, they are often in forms that are difficult to process or are even harmful to health. Therefore, uniform colloidal silicas are generally manufactured using synthetic chemical processes. While established high temperature gaseous synthesis methods fall out of favor in our energy conscious society, liquid synthesis methods are current industrial leaders. The precipitated silica method provides the majority share of commercially produced specialty silicas with its economic advantages predicted to continue to grow in the future. The biomimetic method and microemulsion methods of synthesis provide a superior level of surface chemistry and morphological control than current industrial processes and are the major focus of current silica synthesis research. Movement toward more tailor-made products and ecologically friendly production methods will likely provide incentive for biomimetic methods, in particular, to take more of a market share. However, the lack of procedures to viably scale up the biomimetic and microemulsion methods still forms significant gaps in the literature. In this review, the current methods of colloidal silica synthesis are discussed alongside significant models and mechanisms of silica formation.

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High-resolution dynamic light scattering (DLS), scanning electron microscopy (SEM), time-lapse photography, and attenuated total reflectance Fourier transform infrared spectroscopy were used to analyze the growth kinetics of polyethyleneimine (PEI)-silica particles fabricated from the condensation of hydrolyzed trimethoxymethylsilane (TMOMS) and PEI/phosphate buffer (PEI/PB). Depending on the concentration of hydrolyzed TMOMS and PEI/PB, three stages were identified. We observed the existence of a nucleation time that has never been reported in the literature when TMOMS has been used. During this nucleation time, particles of less than 25 nm were detected using in situ DLS measurements taken every 15 s (high resolution), a DLS timescale resolution not previously reported. In addition, the length of the nucleation time depended mainly on the PEI/ PB concentration, but also TMOMS concentration. The growth stage was evident from the rapid increase of particle size with time. Due to the high resolution of the DLS measurements, a peak could be observed in the particle diameter during particle growth, which corresponds to a secondary population of particles required for the larger particles to further increase in size. Finally, during the equilibrium region, particles reached their maximum diameter that was independent of the concentration of PEI/PB and only changed with concentration of hydrolyzed TMOMS.

Citation for the published paper Citation for this paperTo refer to the repository paper, the following format may be used: A simple mechanistic model is presented here which relates the number of broken contacts in agglomerate due to impact velocity, interparticle adhesion energy and the particle properties of the particles forming the agglomerate. The model is based on the hypothesis that the energy used to break contacts during impact is proportional to the incident kinetic energy of the agglomerate. The damage ratio defined as the ratio of broken contacts to the initial number of bonds is shown to depend on the dimensionless group, , in the form, where V is the impact velocity, E the elastic modulus, D the particle diameter, the particle density and the interface energy. This dimensionless group, , incorporates the Weber number, ( DV 2 / ), which was previously shown to be influential in agglomerate breakage, and may be presented in the form, =WeI e 2/3 , where I e = ED/ . 2The predicted dependency of the damage ratio on the surface energy has been tested using Distinct Element Method (DEM). Four different agglomerates have been formed and impacted against a target for three different values of the surface energy of the primary particles. The simulation results show that the effect of surface energy is better described by the above mechanistic model than by the Weber number alone, as previously used to characterise the impact strength of agglomerates.

Fine coal may be separated from an aqueous suspension of coal and mineral particles through the application of a pure oil. The pure oil preferentially wets and agglomerates only the coal, forming a high quality, granular product. However, the use of the pure oil also comes at a relatively high cost and this cost prohibits commercial implementation of this process. In this work a new, economic binder, was introduced. This binder consisted of a high internal phase water-in-oil emulsion which was 95 vol% water and 5 vol% organic. This type of binder was selected as it possessed the hydrophobic surface functionality of oil while the space filling functionality of the binder was primarily satisfied by the dispersed water droplets within the emulsion. The application of this emulsion in the agglomeration process led to a 10-fold reduction in the organic liquid dosage required to achieve agglomeration as compared a pure oil binder. It was also observed that the agglomeration time required when using the emulsion binder was one order of magnitude less than required when using a pure oil binder. This variation was considered to result from the five orders of magnitude difference in the viscosity of the two binders.

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A high internal phase (HIP) water-in-oil emulsion was used as the binder in the selective agglomeration of fine coal from an aqueous suspension of coal and mineral particles. Traditionally, this agglomeration is achieved by a pure oil, hydrophobic, binder. However, the high cost associated with using pure oil makes the process economically unfeasible. Therefore, the emulsion binder introduced in this work was motivated by the economic need to reduce the amount of organic liquid required in the process. The effect of agitation time during the agglomeration process and the composition of the emulsion on its performance as a binder were investigated. The best result obtained was for a HIP emulsion made from 3 wt% aqueous NaCl and diesel oil with sorbitan monooleate as the emulsifier. This emulsion had a dispersed phase volume fraction of 0.94 and achieved a seven-and-a-half-fold reduction in the amount of organic liquid required to achieve agglomeration.

We have developed a DEM model to study the packing characteristics of iron ore granules. Two important indices in characterising the packing of granules, i.e. the angle of repose (for packing stability) and a size segregation index, were obtained from the simulations. The comparisons of the simulated and experimental angle of repose and size segregation indices showed good agreement, demonstrating that the developed model is capable of predicting the behaviour of iron ore granules during pile formation. The simulation results show that the angle of repose of iron ore granules was greatly influenced by sliding and rolling friction coefficients. The simulation results showed that the decrease in granule size significantly increased the kinetic energy dissipation rate of the discharged granules during the packing process. Therefore, an increase in granule pile stability was observed. The simulation results also demonstrated the presence of significant size segregation of iron ore granules in the pile in the horizontal direction. The average granule size in the outer section of the pile was relatively larger than that in the central section. However, in the vertical direction, due to the interaction of multiple segregation mechanisms, size segregation was not clearly observed.