Adsorption removal of lead and cadmium ions from aqueous solution with coal fly ash-derived zeolite/sepiolite composite

概要

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Various zeolites have been synthesized from coal fly ash (FA) by hydrothermal treatment with NaOH solution. Phillipsite-type zeolite was synthesized selectively from FA (FA-phillipsite), and succeeded in in situ combining the FA-phillipsite with sepiolite to form FA-phillipsite/sepiolite composite. The adsorption behaviour of two harmful heavy metal ions (Pb2+ and Cd2+) were investigated for the FA-phillipsite and FA-phillipsite/sepiolite composite (30 mass % sepiolite). It was found that the NaOH hydrothermal treatment produced not only phillipsite but also Na+-substituted sepiolite. Both the FA-phillipsite and the FA-phillipsite/sepiolite composite showed high adsorbing-ability for Pb2+ (2.90 and 2.68 meq g−1) and Cd2+ (1.62 and 1.74 meq g−1) ions. The adsorption efficiency of the composite was much higher in the measured value than in the calculated one estimated from the maximum adsorbing-ability of the untreated sepiolite. This indicates that the Na+-substituted sepiolite in the composite has excellent adsorbing-ability for Pb2+ and Cd2+ ions. Since sepiolite has superior forming performance, the FA-derived phillipsite/sepiolite composite powder was able to be molded into various shapes e.g. pellet and tube. The FA-phillipsite/sepiolite composite is expected to be a new adsorbent for practical use.