BAUXITE: TO REMEDIATE HEAVY METAL CONTAMINATED WATER?

Bauxite, the principal ore of aluminum has a high potential as an adsorbent to treat contaminated water to remove toxic metals due to its large specific area and effective adsorption capacity. However, raw bauxite has not been widely applied for this purpose. Two types of bauxite (B1 and B2), sampled in Pontotoc County, Mississippi were used in this study to remove heavy metals from water. Mono-element and multi-element solutions were prepared by introducing Ni²⁺, Co²⁺, Cu²⁺, and Pb²⁺ ions at concentrations of 10µg/L and 100µg/L to water. The solutions were left in contact with powdered, acid-washed, and air-dried bauxite for 24 hours and filtered. Temperature, ionic strength, and pH of the solutions were kept constant. The filtrates were analyzed using inductively coupled plasma-mass spectrometer (ICP-MS) at the University of Mississippi.

Both bauxites removed a notable amount of all the elements from water at both concentrations. B2 had higher percent adsorption from mono-element and multi-element solutions at 10 µg/L. However, in general, both samples showed similar percent adsorptions at 100 µg/L. The percent adsorption by B1 significantly increased with increase in initial concentration of ions. The effect of initial metal ion concentration on adsorption by B2 was almost negligible, which makes B2 an effective adsorbent independent of the concentration of metals in water. Generally, bauxite showed a higher affinity for Cu²⁺, but other heavy metal ions present in water can interfere this selective adsorption. Scanning electron microscopy with energy-dispersive X-ray spectroscopic (SEM-EDS) analysis detected high concentrations of Al, Fe, Si, and O with minor amounts of Ti, S, Na, and K in bauxite. Initial SEM-EDS analysis of Pb²⁺-treated bauxite confirmed the presence of trapped-Pb, but the experiments will be extended with higher concentrations in order to identify stronger peaks at EDS. Initial data confirms that raw bauxite removes heavy metals from water through chemical adsorption reactions. Substrates such as Al₂O₃, Fe₂O₃, and TiO₂ could act as possible adsorption sites for heavy metals. Type of bauxite, initial metal concentration, and interference by metal ions influence bauxite adsorption.