The experiments on concentration of hydrothermal solutions by membrane filters for silica sols production were carried out. Three types of membrane processes were tested: microfiltration, ultrafiltration, reverse osmosis. Temperature of solution varied from 20 to 90 0C. Selectivity of membrane layers with respect to colloidal silica particles and molecules of orthosilicic acid was determined in the experiments. Silica sols with SiO2 content up to 940 g/dm3 (62.25 mass %) and particles radii of 29-135 nm were obtained by the ultrafiltration. Silica powders with the specific surface of 110-400 m2/g, mean pores diameter of 3-10 nm, pores volume of 0.2-0.3 sm3/g were obtained by cryochemical vacuum-sublimation drying of sols with liquid nitrogen use. Particles sizes of the powders are within the range of 10 - 100 nm. The characteristic of powders extracted from silica sols such as particles sizes, diameters, surface areas, pores volumes were studied. The methods of scanning electron microscopy, X-ray phase analysis, thermogravimetry, low temperature nitrogen adsorption were used. In accordance with measurement results the influence of process conditions on powders characteristics was determined.

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