In situ co-adsorption of arsenic and iron/manganese ions on raw clays

The use of clays as effective arsenic sorbents has been strongly limited due to their low pHZPC and cation active behaviour in aqueous systems at pH > 3.5. A simple Fe/Al/Mn pre-treatment can significantly improve their sorption affinity to oxyanions, including arsenites and arsenates. The dynamics of arsenic adsorption from groundwater is also controlled by dissolved Fe/Mn ions, which behave as promoters of As adsorption, or competitors to adsorption sites. Low grade calcinated kaolin (MT) and bentonite (BT) were used as clay sorbents. Arsenic adsorption on raw clays without presence of Fe/Mn ions is very slow and limited. During co-adsorption the Fe/Mn ions and As oxyanions were adsorbed together onto a sorbent surface. Both Mn and Fe particles demonstrated a good sorption affinity to the clay surface, but only Fe particles supported As adsorption considerably (80% of As were removed in Fe/As system, while < 30% only in the Mn/As system). The kinetics of co-adsorption compared to the use of Fe/Mn pre-modified sorbents indicated a more dynamic process, while all mechanisms corresponded to the first order run (k ≈ 9.10− 6– 1.10− 4 s− 1). Arsenic was strongly stabilized in pre-modified sorbents.

Adsorption affinity of raw aluminosilicates (bentonite — light symbols and metakaolin — dark symbols) to arsenic oxyanions in presence of dissolved Fe2+/Mn2+ ions.The dynamics of arsenic adsorption to raw clays has been controlled by dissolved Fe2+/Mn2+ ions, which behaved as the promoters of adsorption procedure, or conversely, as the competitors to active sorption sites. During co-adsorption both Fe/Mn ions and As oxyanions were adsorbed together onto sorbent surface. Fe and Mn particles demonstrated a high sorption affinity to sorbent surface, but only Fe particles supported As adsorption significantly.Figure optionsDownload as PowerPoint slideHighlights
► Fe–As or Mn–As co-adsorption from aquatic environment to clay surface.
► Iron improve arsenic adsorption significantly.
► In situ co-adsorption was compared to As adsorption on Fe/Mn-modified clays.