Potential Environmental Applications of Pure Zeolitic Material Synthesized from Fly Ash

A pure 4A/X (60/40) zeolite product was synthesized from silica extracts of the Meirama fly ash in northwestern Spain. A high cation-exchange capacity (4.7 meq/g) was obtained for the zeolitic material. The potential application of this coal fly ash conversion product for decontamination of high heavy metal waters was evaluated using three high heavy metal waters from acid mine drainage around the pyrite Huelva belt. The results were compared with those obtained with an equivalent pure commercial synthetic zeolite. A considerable reduction in the heavy metal content was attained (Zn from 174 to <0.1 mg/L, Cu from 36 to 0.1 mg/L, Fe from 444 to 0.8 mg/L, Mn from 74 to <0.1 mg/L, Pb from 1.5 to <0.1 mg/L, and Cd from 0.4 to <0.1 mg/L), even in high Ca and Fe waters using zeolite doses from 5 to 30 mg/L. Both precipitation and cationexchange processes accounted for the reduction in the pollutant concentration in the treated waters. Leachable hazardous elements from coal fly ash, such as Mo, B, As, V, and Cr, were not fixed in the synthesis of pure zeolites from the silica extracts. Consequently, they did not restrict the potential applications of this material as an ion exchanger, unlike the zeolitic material obtained from fly ash by direct alkaline conversion.