Enhancement of the Dewetability Characteristics of Fine Silica Particles


Abstract: The dewatering of fine particles is the most difficult part of fine particle processing in preparation plants. The difficulty is due to the fact that fine particles have a higher specific surface area than coarse particles. For this reason, the currently used dewatering techniques (i.e., vacuum, pressure and centrifugal filters) cannot produce a desired moisture content of a filter cake that can be directly used in markets; therefore, most filter cakes are fed to thermal dryers. Thermal drying is costly, and creates environmental pollution where the operation is located. In the present study, dewatering tests were conducted on fine size silica (SiO$_{2}$) powder in a vacuum filter using different chemicals. These include electrolytes, dodecylamine and a hydrophobizing agent. The test results showed that the electrolytes neutralized the particle surface charge in an aqueous medium and coagulated the suspension, which should assist moisture reduction of the particles. The dodecylamine made the particle surface slightly hydrophobic at pH 9.5 in order to adsorb the hydrophobizing agent on the fine silica surfaces. Afterwards, the particle surface became super hydrophobic; for example, the contact angle of the silica powder was improved from 44° to 89°, which was determined using the newly developed thin layer wicking method. As a result, the moisture content of the filter cake was decreased from 26.3% to 7.4% at 1.5 cm cake thickness and 85 kPa vacuum pressure. It was, therefore, concluded that changing the surface properties of the silica particles helped lower the dewatering cost of the fine particles and environmental concerns in plants.

Keywords: Silica, Lime, Coagulation, Surface hydrophobicity, Dewatering aid, Kinetics and moisture content.

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