Synthesis of zeolites from fly ash at pilot plant scale. Examples of potential applications

This study focuses on the synthesis of zeolites from Spanish fly ashes at l aboratory (g and kg sample size) and pilot plant (metric ton sample size) s cales, and on the potential application of the synthesized zeolitic materia l. To this end, eleven Spanish fly ashes were selected and characterized in detail. A matrix of experimental parameters was built to optimize the synt hesis of mono-mineral zeolite products from the different fly ashes. This w as achieved by using Parr digestion bombs, KOH and NaOH as activation agent s, under experimental conditions ranging from T = 150 to 200 degreesC, t = 3 to 48 h, C = 0.5 to 5 M, P = 4.7 to 15.3 atm, and solution/sample ratio f rom 2 to 18 mi gl Subsequently, experiments to synthesize NaPl zeolite were scaled up to kg sample and pilot plant scale. The zeolitic material obtain ed at these two scales was very similar. The NaPl zeolite content was estim ated as 40%. The major potential applications of the zeolites obtained were tested by determining the cation exchange capacity (CEC) with ammonium and different heavy metals. The results showed CEC values from 160 to 260 meg. 100 g (1) for NaPl, herschelite, KM, linde F and K-chabazite for the major ity of the cations investigated. The zeolitic material synthesized at pilot -plant scale yielded the following CECs for these heavy metals: 68 meq. 100 g(-1) for Ni2+ 90 meq. 100 g(-1) for Cd2+, 95 meq. 100 g(-1) for Zn2+, 98 meq. 100 g(-1) for Pb2+, 110 meq. 100 g(-1) for Fe2+. 130 meq. 100 g(-1) fo r Ba2+, 210 mu eq. 100 g(-1) for Cu2- and 260 meq. 100 g(-1) for Cr3+. (C) 2001 Elsevier Science Ltd. All rights reserved.