The synthesis of nano-silica is gaining the attention of researchers due to its numerous applications in various fields such as medicine, the food industry, catalysis, agriculture and construction, amongst others, because of its unique physicochemical features. However, achieving its facile synthesis and finding inexpensive source material that is locally available requires further exploration for its large-scale production. This paper reports the synthesis and characterization of nano-silica from locally available laterite clay using the sol-gel method. The product was analysed using X-ray florescence, X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. It was observed that the product was spherical, agglomerated and amorphous in nature. The obtained nano-silica was found to have 97% and 95% purity for sodium hydroxide and potassium hydroxide, respectively. The synthesized nano-silica is expected to play pivotal role as a pozzolanic activator in the construction industry.

The influence of anionic dispersing agents, such as sodium poly(acrylic acid), sodium hexametaphosphate, and sodium silicate on the dissolution of crude kaolin was examined by measuring the dissolved metals produced in the absence and presence of dispersing agents. For this purpose, the rheological and structural changes caused by the dissolution of kaolin metal constituents were studied in batch mode using several parameters, namely, solids (wt.%), pH, contact time (aging), and dispersing agent dose. A noteworthy increase in kaolin dissolution was caused by the presence of dispersing agents, particularly poly(acrylic acid) and sodium hexametaphosphate. These agents produced conspicuously large amounts of dissolved Al in comparison to the other experimental treatments. Little dissolved Si was measured under similar conditions in distilled water, but the amount of Si released using dispersing agents was nearly double that observed in distilled water only. Excess dispersing agents interacted with kaolin and dissolved accessory elements in the kaolin (i.e. Fe, Ca, Mg) and thus released enough Fe to form a stable Fe—dispersant complex. The present study showed that this phenomenon also contributed to a significant increase in the release of dissolved Al and Si through complexation.

Kaolinite is a common gangue mineral in iron ore and sodium silicate has been used widely as a dispersant of silicate gangue minerals including kaolinite in various iron-ore flotation methods over a wide range of pH. Its actual dispersive effect on kaolinite under iron-ore flotation conditions has received very limited attention, however. The presence of hydrolyzable metal cations in process water further complicates sodium silicate—kaolinite interactions. In the present study, the dispersive effect of sodium silicate on kaolinite particles in distilled water as well as in CaCl2 and MgCl2 solutions was investigated systematically through electrophoretic mobility and colloid-stability studies. The studies were based on controlled pH, which eliminated the dispersive effect of sodium silicate induced by increasingpulp pH, in order to simulate the conditions of iron-ore processing. With pH controlled at constant levels, sodium silicate dispersed kaolinite only when positively charged sites were present on kaolinite surfaces and the zeta potential of kaolinite was more negative than ~−30 mV. Over the pH range from 5 to 10.5, a significant dispersive effect of sodium silicate was only observed at pH 7. In process water, when Ca and Mgwere present, the strong coagulation of kaolinite particles caused by the hydrolyzable metal cations could not be dispersed effectively with sodium silicate.