George R. Brown Convention Center, Exhibit Hall E
Sorption of heavy metals and NH4+ by clinoptilolite tuff from Oaxaca, Mexico, containing 55 % clinoptilolite, CEC 1.07 meq/g, adsorbs from 0.1 N solutions Cr3+ 0.121 mg/g, Ni2+ 0.147, Cu2+ 0.603, Mn2+ 0.990, Zn2+ 1.045, Hg2+ 1.303, Cd2+ 1.855, NH4+ 5.742, Pb2+ 10.877 and Ag+ 17.366 mg/g. Adsorption by Ca2+-exchanged tuff increases to Cr3+ 2.507 mg/g, Ni2+ 4.609, Cu2+ 6.545, Mn2+ 5.274, Zn2+ 5.608, Hg2+ 21.965, Cd2+ 13.600, NH4+ 13.464, Pb2+ 25.795 and Ag+ 41.691 mg/g. Selectivity Ag+>NH4+>Pb2+>Cd2+>Hg2+>Cu2+>Mn2+>Zn2+>Cr3+>Ni2+. Sorption from cation+Ca2+ solutions 0.1 to 0.005 N follows the Langmuir model establishing maximum sorptions by the natural tuff of Cr3+ 3.180 mg/g, Ni2+ 4.135, Cu2+ 5.282, Mn2+ 2.802, Zn2+ 4.282, Cd2+ 5.302 and Pb2+ 18.336 mg/g, selectivity Pb2+>Cd2+>Cu2+>Zn2+>Ni2+>Cr3+>Mn2+. Ca-saturation improves sorption of Cu2+ by 7.08 %, Pb2+ 8.60 % and Ni2+ 25.66 % but reduces Cr3+ by 19.87 %, Zn2+ 1.33 %, Mn2+ 44.61 % and Cd2+ 40.11%. Cation and Ca2+ are adsorbed simultaneously at levels below the CEC of the tuff without precipitation of hydroxy complexes. Ca2+ does not limit the adsorption of cation, rather it eases and stabilizes their sorption.
Sorption by clay containing 85 % montmorillonite, CEC 0.69 meq/g adsorbs from 0.1 N solutions less than 1 meq/g of Ba2+, Mn2+, K+ and Cd2+, between 1.409-1.559 meq/g of Ag2+ and Ni2+, 3.293-3.730 meq/g of Pb2+ and Hg2+, Cu2+ 4.341 meq/g, Cr3+ 4.117 meq/g and Zn2+ 4.104 meq/g. Selectivity Cu2+>Cr3+>Zn2+>Hg2+>Pb2+>Ni2+>Ag2+>Ba2+>Mn2+>K+>Cd2+. Maximum sorptions from 0.1 N solutions of cation + Ca2+ by montmorillonite are Hg 31.74 mg/g, Zn2+ 20.84, K+ 14.48, Cd2+ 9.86, Ni2+ 8.27, Ba2+ 6.59 and Mn2+ 3.82 mg/g; by Ca2+-exchanged montmorillonite they are Zn2+ 39.61 mg/g, K+ 16.62, Ba2+ 14.61, Ni2+ 11.98 and Cd2+ 11.35 mg/g. Cr3+, Cu2+ and Pb2+ precipitate and immobilize leaving solutions free of metal but enriched in Ca2+ desorbed from the clay.