Chromate Adsorption by a Goethite-based Adsorbent in the Presence of Major Competing Ions

Cr(VI) adsorption on a goethite-based adsorbent Bayoxide E33RTM (E33) was investigated over a wide range of pH and ionic strength in the absence and presence of major co-existing ions (calcium, magnesium, silicic acid, phosphate and sulfate) in groundwater. Cr(VI) adsorption decreased as pH shifted from acidic to alkaline as is typical for oxyanions. Background ionic strength did not impact Cr(VI) adsorption. This fact may suggest that Cr(VI) forms inner-sphere complexes on the adsorbent. The adsorption edge data suggest that calcium and magnesium slightly enhanced Cr(VI) adsorption. Silicic acid strongly bound to E33 and reduced the Cr(VI) adsorption at pH = 6-8. Phosphate is the ion that impacted the Cr(VI) adsorption most significantly over a wide range of pH. Sulfate only suppressed Cr(VI) adsorption at low pH. Most of the data obtained compares well with that from previous studies. The order of relative affinity of anions on E33 is phosphate > silicic acid > Cr(VI) > sulfate > magnesium ∼ calcium.