Zinc removal from acid rock drainage by clinoptilolite in a slurry bubble column

Zinc uptake by adsorption from zinc-spiked acid rock drainage (ARD) on natural clinoptilolite was investigated in a slurry bubble column. The effects of contact time, adsorbent particle size, initial aqueous zinc concentration, adsorbent dosage and initial solution pH on zinc immobilization were examined. Langmuir and Freundlich adsorption isotherm equations were fitted to the experimental data. Finer clinoptilolite particles adsorbed more zinc, probably due to more accessible surface area. Zinc adsorption improved as pH increased from 2 to 5, probably due to competition of H+ at low pH. A slurry loading of 200 g clinoptilolite per kilogram ARD and an initial aqueous pH of 4 appear to be suitable conditions for removing zinc from ARD. While the aqueous concentration of zinc in ARD was reduced significantly in a single run, 8 cycles of adsorption in series were needed to reduce the zinc concentration to the regulated level.