EFFECTS OF IONIC STRENGTH ON ARSENATE ADSORPTION TO IRON OXIDES

The extraction of gold from gold bearing sulphide minerals like arsenopyrite results in the release of arsenic into the environment which adversely affect the health of ecosystems. Adsorption is an important process that impacts the fate and transport of metal contaminants in soils and aquatic environments and can be applicable to the removal of arsenic as well. Under oxidizing conditions, the common form of arsenic is arsenate (H_xAsO₄), which strongly adsorbs to many mineral surfaces, especially to aluminum and iron oxides and hydroxides via inner-sphere and/or outer-sphere complexation. Those minerals are widely abundant in nature and environmentally friendly such that, they tend to be used as adsorbent for arsenate removal in water. Many researchers have explored the use of iron oxides as a good adsorbent for arsenate removal from water and also explored the mechanisms of arsenate adsorption. However, only few studies have carefully considered the effect of ionic strength on arsenate adsorption to iron oxides. In this study, we synthesize two iron oxides, hematite and goethite, and seek to investigate the dependence of arsenate adsorption on ionic strength in batch adsorption isotherm experiments.

Key Words: arsenate adsorption; inner-sphere adsorption; ionic strength; outer-sphere adsorption; adsorption isotherm