Author :
Kalbase, M.,Racz, G. J.,Loewen-Rudcers, L. A
Abstract :
Adsorption of Zn from aqueous solutions of ZnCl***2 by hydrated Al***2O***3 and Fe***2O***3 was highly pH-dependent and increased markedly with increasing pH. Fe***2O***3 had a higher Zn adsorption capacity, at epuivalent pH values, than Al***2O***3. Hydrogen ions were released upon adsorption of Zn**2+ on the surface of Al***2O***3 and Fe***2O***3, suggesting that surface aquo (-OH***2)and hydroxo (-OH) groups were involved in Zn adsorption. The molar ratio of H**+ released to Zn**2+ adsorbed onto Fe***2O***3 increased from 1.53 to 1.96 as suspension pH increased from 5.93 to 6.96, whereas the molar ratio of adsorbed Cl- to adsorbed Zn**2+ decreased from 0.44 to 0.08. The proportion of adsorbed Zn**2+ that could be replaced with Ba**2+ was approximtely the same as the molar ratio of adsorbed Cl- to adsorbed Zn**2+. Similar results were obtained for Al***2O***3. It was postulate that two types of adsorption, specific and nonspecific, depending upon reversibility (exchangeability with Ba**2+), accurred. Specific adsorption involved adsorption of Zn**2+ and release of two H+ ions for each mole of Zn**2+ adsorbed and accounted for 60 to 90 percent of total Zn adsorption by Fe***2O***3. An olation bridge structure between Zn**2+ and two surface -OH***2 groups was postulated. Nonspecific adsorption of Zn accounted for 40 to 10 percent of the total Zn adsorption, and was thoughet to involve adsorption of Zn**2+ plus Cl- and the release of one H+ ion for each mole of Zn**2+ adsorbed. A single-bond structure in which ZnCl+ replaced one H+ from surface -OH***2 groups was postulated...
