The removal of aqueous silica from dilute aqueous solution |
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| Authors: | CP Huang |
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| Institution: | Department of Civil Engineering, University of Delaware, Newark, Del. USA |
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| Abstract: | The adsorption characteristics of orthosilicate on hydrous γ-Al2O3 from dilute aqueous solution (10?4 to 10?3 M) at constant ionic strength (0.1M NaCl) was investigated in the laboratory.The extent of adsorption is affected by pH, concentration of silicate, or the relative concentration of silicate and oxide surface. With short reaction time (24 hours), adsorption is the major interfacial reaction and follows an S-type adsorption isotherm. The steepness of the S-curve isotherm is influenced by the degree of equilibrium. The slower the adsorption reaction is, the flatter the S-curve becomes.Two steps, an initial fast followed by a second slow, of silicate removal were observed. The first fast step, which lasts for about one to two hours, depends greatly on pH and has the following expressions: ?dSi]/dt = 1.3 × 10?3 A]2H+]?0.5Si]1.5; pH < 9 and ?dSi]/dt = 4.0 × 1010 A]2H+]Si]1.5; pH > 9. The second slow step is a first-order form with respect to the concentration of silicate. The specific rate constant depends on pH, concentration of silicate and surface area.Specific chemical energy contributes significantly to the adsorption of silicate and a value of ??12RT was found. |
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