Kinetics of Sorption of Zinc by Goethite
Abstract
Zinc sorption by synthetic goethite (surface area 95.2m2 g-1; pH(PZC) 7.9) and production of acidity accompanying the sorption were studied as functions of reaction time and pH.
Kinetics of Zn sorption by goethite were conducted at 25°C at a single initial solution Zn concentration of 2.0 mg Zn (3.06 x 10-5M) at pH 5.4, 7.0, 7.8 and 8.5.
Zinc sorption increased with increase in pH. At pH 5.4 and 7.0, there was an initial rapid sorption that was followed by a slow one that lasted many hours. At pH 7.0 and 7.8, 50% of the added Zn was removed from solution in about ten minutes. At pH 8.5, however, sorption was so fast and complete as to be maximum (121.6 unmolest Zn g1) in less than ten minutes.
A lag in the release of H was observed at the initial sorption reaction times at pH levels below pH 8.5, and this lag suggested an initial Zn sorption reaction that was nonproteolytic, to be later followed or accompanied by a photogenic reaction.
At pH 7.8 and 8.5, the ratio of 1-1* released/ Zn sorbed at the final reaction times were 1.7 and 1.9, respectively. A release of two moles of Fl+ accompanying a sorption of one mole of Zn was postulated to result I from a hydrolysis of Zn together with an exchange of the hydroxy Zn species with protons at the geothite surface:
Zn2+ + H2O Zn0H+ ; Zn0H+ + SH = SZnOH + where SH represents adsorption sites on goethite surface.
Zinc sorption by synthetic goethite (surface area 95.2m2 g-1; pH(PZC) 7.9) and production of acidity accompanying the sorption were studied as functions of reaction time and pH.
Kinetics of Zn sorption by goethite were conducted at 25°C at a single initial solution Zn concentration of 2.0 mg Zn (3.06 x 10-5M) at pH 5.4, 7.0, 7.8 and 8.5.
Zinc sorption increased with increase in pH. At pH 5.4 and 7.0, there was an initial rapid sorption that was followed by a slow one that lasted many hours. At pH 7.0 and 7.8, 50% of the added Zn was removed from solution in about ten minutes. At pH 8.5, however, sorption was so fast and complete as to be maximum (121.6 unmolest Zn g1) in less than ten minutes.
A lag in the release of H was observed at the initial sorption reaction times at pH levels below pH 8.5, and this lag suggested an initial Zn sorption reaction that was nonproteolytic, to be later followed or accompanied by a photogenic reaction.
At pH 7.8 and 8.5, the ratio of 1-1* released/ Zn sorbed at the final reaction times were 1.7 and 1.9, respectively. A release of two moles of Fl+ accompanying a sorption of one mole of Zn was postulated to result I from a hydrolysis of Zn together with an exchange of the hydroxy Zn species with protons at the geothite surface:
Zn2+ + H2O Zn0H+ ; Zn0H+ + SH = SZnOH + where SH represents adsorption sites on goethite surface.
