Abstract
Diatomite, wood fly ash and their mixture with TiO2 were tested as adsorption substrates for copper and cadmium cations removal from wastewater. Raw diatomite and wood ash were pretreated and stabilized by washing and were comparatively investigated as adsorption substrates for heavy metals. Further on, a composite mix of pretreated diatomite and wood ash was obtained by mixing with nano-structured TiO2, to increase the surface area of the substrate materials. The novel adsorbent was investigated in terms of crystallinity (XRD), surface properties (AFM, SEM, porosity and BET surface) and surface chemistry (EDX, FTIR). Equilibrium studies demonstrated that the novel material has a high capacity for Cu2+ and Cd2+ removal, showing removal efficiencies above 80% for cadmium and of 99% for copper cations, in optimised adsorption experiments. In this paper the kinetic mechanisms of the cation adsorption are discussed and are correlated with the substrates properties.
Highlights
As part of their treatment, diatomite and wood ash were washed and the final pH and conductivity values of the supernatant are quite different, proving that these materials contain different amounts of soluble oxides (Na2O, K2O, lime etc.), exceedingly higher for the wood ash, as Table 1 shows. These values confirm that the wood ash has an increased content of strongly alkaline soluble compounds, leading to much bigger pH values than diatomite, the conductivity is similar
The results show that the adsorption efficiency on diatomite is low and this can be a combined effect of the lower surface charge and lower specific surface
The results obtained in optimized conditions showed moderate increase in the cadmium adsorption and a strong increase of copper adsorption, up to 99%, Figure 7
Summary
To fulfill the industrial requirements, low-cost adsorbents are intensively studied, mainly based on natural compounds (red mud [8], natural zeolites [9], bentonite [10], clay [11], and diatomite [12] moss peat [13]) or on wastes: bone char [14], activated sewage sludge [15], wood ash lime and fume dust [16] Fly ash is another pollutant by-product, raising big environmental problems; the use of this waste as second raw material, in various applications becomes a sustainable solution [17, 18]. The structural and surface properties of the components in this adsorbent and of their mix are presented in this paper, along with their efficiency in removing two heavy metal cations, cadmium and copper
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