Silica Extraction from Hydrothermal Solutions by Membrane Filters

Abstract

The experiments on concentration of hydrothermal solutions by membrane filters for silica sols production were carried out. Three types of membranes were tested. The first type was ceramic membrane filters with diameters of pores 0.1-0.3 microns. The second type was filters with pores sizes in the range of ultrafiltration – 0.01-0.001 microns. The third one was filter with reverse osmosis membrane with diameters of pores in the range 0.001-0.0001 mm. 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 600 g/dm3 (43,0 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.