2003 Volume 29 Issue 3 Pages 389-394
For the purpose of adsorptive removal of penta- and tri-valent arsenic existing as arsenate and arsenite anions, respectively, in water, a novel adsorption gel was prepared by crosslinking pectic acid with formaldehyde. In order to obtain fundamental information on the adsorption behavior of this gel, before the adsorption of arsenic, the order of selectivity among metals which exist as cationic species in water was investigated and found to be as follows: Sn(IV) ≫ Sn(II) ≫ Pb(II) ~ Fe(III) ≫ Cu(II) > Al(III) ≫ Zn(II) ~ Ni(II) ~ Ca(II) ≧ CO(II) > Mn(II). The maximum loading capacity for ferric ion was 0. 57 mol/kg-dry gel.
Because the ferric iron is known to have a high affinity to arsenate and arsenite anions, iron(III)-loaded crosslinked pectic acid gel was prepared to investigate its adsorption behavior for these arsenic species in water by means of batch and column tests. Arsenate was predominantly adsorbed in the weakly acidic region, while arsenite was predominanthly adsorbed in the weakly alkaline region. Arsenate was found to be selectively adsorbed on the gel in the presence of excess chloride and sulfate ions in both of batch and column adsorption tests. In the adsorption tests using a packed column, arsenate exhibited a more favorable breakthrough profile than arsenite. Arsenate and arsenite were eluted from the column with 1 M hydrochloric acid, together with the loaded iron. Arsenate was also eluted with 1 M sodium hydroxide solution together with a small amount of the loaded iron.
