Date of Award
M.S. in Engineering Science
Inoka H. Widanagamage
Brian F. Platt
Andrew M. O'Reilly
Bauxite, the principal ore of aluminum is a potential low-cost sorbent to treat heavy metal-contaminated water. This work studied the ability of raw bauxite to adsorb Pb2+, Cu2+ , Ni2+, and Co2+ ions in natural waters and the dependency of the sorption efficiency on the initial metal ion concentration in water, contact time, the ‘type’ of bauxite, and the effect of coexisting metals. Goethite-rich (B1) and kaolinite-rich (B2) bauxites were sampled in Pontotoc County, Mississippi. Single element and multi-element (ME) solutions were prepared by introducing the metals at concentrations of 10, 100, and 500 ppb in lake water. The solutions were left in contact with 0.25 g of prepared bauxite powder over contact periods of 3, 6, 12, 24, and 48 hours without changing other physicochemical parameters. The filtrates were analyzed using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Bauxite mineralogy was examined using X-ray Diffraction (XRD) and Scanning Electron Microscope with Energy Dispersive X-ray spectroscopy (SEM-EDS).
Except in certain Ni2+ -containing systems, bauxite could remove metals from the water. Overall, the percent sorption tends to decrease with increase in initial metal concentration of the metals tested. Some systems particularly Pb2+ - and Cu2+ -containing recorded the highest percent sorption (>90%) at 100 ppb but it dropped (around 20-40%) at 500 ppb. Metal uptake generally increases with increase in initial metal concentration but the increment between the 100 ppb and the 500 ppb systems is often less pronounced. The sorption by B1 is relatively more dependent on the initial metal concentration. Overall, the removal efficiency of B2 is slightly higher. A clear dependency of sorption on contact time was not observed. Bauxite is selective towards Cu2+ and Pb2+ but the near-complete removal of Cu2+ in some systems suggests that Cu2+ is favored. Co2+ and Ni2+ seem to have similar affinities toward bauxite, but Ni2+ showed negative percent sorption values at certain longer contact times and higher concentrations. The removal efficiencies of both bauxites decreased in the ME-experiments. Adsorption is possibly Langmuirtype, suggesting chemisorptive monolayer formation. Fe-Al Oxyhydroxide and clay surfaces are the possible adsorption sites in bauxite that bind metals via specific adsorption and ion exchange.
Herath, Hashindra Kumari, "REMOVAL OF HEAVY METALS FROM WATER USING NATURAL BAUXITE" (2021). Electronic Theses and Dissertations. 2158.
Geology and Geological Engineering