Abstract
Hydrous stannic oxide (HSO) was synthesized in the laboratory and its systematic Cr (VI) adsorption behaviour was studied by means of batch experiments. The particle size of HSO used was in the range of 140 to 290µm. The variable parameters viz. the effects of pH, concentration of Cr (VI) and time of contact etc. are here reported. The optimum pH and time of contact required for maximum adsorption was found to be 2.0 and nearly 90 min, respectively. The experimental equilibrium adsorption data are tested for the Langmuir, Freundlich, Temkin and Redlich-Peterson equations. Results indicate the following order to fit the isotherms equations: Redlich- Peterson > Temkin > Freundlich > Langmuir. Different kinetic models have been applied to fit the experimental kinetic data. The results are compared, and indicated that the best fit is obtained with the Lagergren or pseudo first-order and the power-function models. A discussion on the adsorption mechanism with respect to the thermodynamic parameters leads to two possible interpretations: One is the exothermic nature of the adsorption process and the other is the ion-ion type electrostatic interaction between the adsorbent and adsorbate ion. Keywords : Cr (VI), adsorption mechanism, hydrous stannic oxide(HSO), isotherm, kinetics, thermodynamic parameters Water SA Vol. 31(4) 2005: 597-602
Highlights
Chromium, an element of 6th group in the latest IUPAC periodic table, exists in the aqueous environment mainly in +III and +VI states. Cr (III) and +VI states
Cr (III) is non-toxic, and an essential species to mammals that helps the body to control blood-sugar levels in trace concentrations, but toxic to fish when present in water above 5.0 mg/l (Alloway and Ayres, 1997)
This study reports the pH effect, contact time and kinetic study on Cr (VI) adsorption
Summary
An element of 6th group in the latest IUPAC periodic table, exists in the aqueous environment mainly in +III and +VI states. In under-developed countries like India discharge wastewater into the surface water containing Cr (VI) after reduction to the trivalent state. Surface adsorption is found to be an important basis for the treatment of toxic element-contaminated water. Numerous adsorbents such as goethite (Mesuere and Fish, 1992), clay (Lazaridis et al, 2001), layered double hydroxides (Goswamee et al, 1998), used tyres and sawdust (Hamadi et al, 2001), activated carbon (Lalvani et al, 1998; Han et al, 2001), zeolite (Tahir et al, 1998; Haggerty and Bowman, 1994), feldspar Hydrated stannic oxide (HSO) is a cheap, non-toxic and an insoluble compound showing anion-exchange properties (Amphlett, 1964). This study will contribute to an understanding of the Cr (VI) adsorption mechanism using hydrous stannic oxide as the adsorbent
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