Lead sorption performance on active silica derived from fly ash.

Abstract

The object of this study was to estimate the sorption property of active silica derived from fly ash after separation of silica and aluminum. The specific surface area of active silica enlarged to 115 m(2)/g was compared with the original fly ash (4 m(2)/g). Field emission scanning electron microscopy displayed the active silica, which looked like a honeycomb or curly layer with many lamellae that formed many mesopores. The uptake kinetics indicated that the residual concentration of Pb(2+) in the aqueous solution decreased rapidly from the initial 1.25 mg/L to less than 10 μg/L within 45 min. The removal efficiency of Pb(2+) on active silica was pH dependent. The increase in pH value promoted Pb(2+) removal because the negative surface provided more electrostatic attraction sites. A stepwise non-linear isotherm was obtained because the lamellae of active silica provided a heterogeneous surface with various kinds of active sites. The maximum sorption amount of Pb on active silica was more than 90 mg/g, which was better than some pristine-activated carbon.