Adsorption of Arsenate on Clays

Abstract

The adsorption of arsenate by four adsorbents; Mae Rim Clay (Mae Rim), Yellow
Clay (Hang Dong), Red Clay (Doi Saket) and Laterite (Pa Sang) (Thailand) were studied.
The rate of arsenic adsorption from solution by four adsorbents are rapid for the first few
hour and then approach equilibrium within 24 hours at 100 mg L-1 initial arsenate
concentration. The amount of arsenate adsorbed increases with increasing pH and reaches a
maximum at pH 5 for Mae Rim Clay and Red Clay, at pH 7 for Yellow Clay and at pH 6 for
Laterite, then decreased afterward when the arsenate concentration range from 50 to 200 mg
L-1. The Freundlich isotherm equation was successfully used to describe arsenate adsorption
over an initial concentration range of 25 to 200 mg L-1 arsenate for all adsorbents. The
arsenate sorption capacity of adsorbents increased in the order: Mae Rim Clay < Yellow
Clay < Laterite < Red Clay at pH 4 and 9, but increased in the order: Mae Rim Clay <
Laterite < Red Clay < Yellow Clay at pH 7.
Keywords: arsenate / adsorption / adsorption isotherm / adsorbent / equilibration time