The U.S. Bureau of Mines is investigating the use of natural zeolites to remove metals from acid mine drainage (AMD). The loading characteristics ofA1 3 +, Ca 2 +, eu 2 +, Fe 2 +, H+, Mg 2 +, and Zn'+ were studied for samples of clinoptilolite from Barstow, CA, Buckhorn, NM, and Hector, CA. The relative order of cation selectivity was Zn 2 + > Ca 2 +,eu 2 + > Fe 2 + >ff+> Mg'+> Al 3 +. The order of exchange capacity for the three zeolites was Hector> Barstow> Buckhorn, which corresponds to the Na content of the three zeolite samples. An acid mine drainage sample from the Rio Tinto Mine, an abandoned copper mine in northeastern Nevada, was used to measure the zeolites' cleanup potential. This water contained, in mg/L, 152 AI 3 +, 502 Ca 2 +, 101 Cu 2 +, 595 Fe2+ 13 +, 80 Mn 2 +, and 61 Zn'+. At an approximate flow rate of 4 mL/min (5 bed vol/h), 75% as much zeolite was required to clean the water to drinking water standards when the Hector material was used as compared with the zeolites from Buckhorn or Barstow. Zeolites were regenerated using 25% sodium chloride solutions. Loading and regeneration studies show no detectible degradation in the loading ability of the zeolites through 18 cycles.
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