Removal of Heavy Metals and Other Cations from Wastewater Using Zeolites

Abstract

Zeolites from abundant natural deposits were investigated by the Bureau of Mines for efficiently cleaning up mining industry wastewaters. Twenty-two zeolites were analyzed by X-ray diffraction and inductively coupled plasma analysis (ICP). These included clinoptilolite, mordenite, chabazite, erionite, and phillipsite. The zeolites were primarily in the sodium or calcium form, but potassium and magnesium counter ions were also present. Bulk densities of a sized fraction (minus 40, plus 65 mesh) varied from 0.48 to 0.93 g/cc. Heavy metal ion exchange loading values on two clinoptilolites ranged from 1.6 meq/g for lead to 0 meq/g for mercury in single ion tests. The selectivity series was determined to be Pb>Cd>Cs>Cu(II)>Co(II)>Cr(III)>Zn>Ni(II)>Hg(II). Sodium was the most effective exchangeable ion for ion exchange of heavy metals. Wastewater from an abandoned copper mine in Nevada was used to test the effectiveness of clinoptilolite for treating a multiion wastewater. Aluminum, Fe(III), Cu(II), and Zn in the copper mine wastewater were removed to below drinking water standards, but Mn(II) and Ni(II) were not. Calcium and NH₄ were absorbed preferentially to all heavy metal cations except Pb. Adsorbed heavy metals were eluted from zeolites with 3-pct NaCl solution. Heavy metals were concentrated in the eluates up to 30-fold relative to the waste solution. Anions were not adsorbed by the zeolites.