Abstract
For the first time, hybrid organic–inorganic geopolymeric foams were successfully used as monolithic adsorbents for the removal of metallic ions pollutants from wastewaters. The foams were realized by the in situ foaming of a hybrid geopolymer obtained by a reaction of metakaolin and polysiloxane oligomers under strong alkaline conditions and then cured at room temperature. In this way, porous materials with densities ranging from 0.4 to 0.7 g/cm3 and showing good mechanical properties were produced. With the aim of producing self-standing monolithic adsorbents for the removal of metallic ions pollutants from wastewaters, these porous hybrid geopolymers were subjected to a washing pretreatment with ultrapure water, dried, and then used for absorption tests by dipping them into an aqueous solution with an initial concentration of 20 ppm of Pb2+, Cd2+, Cu2+, and Zn2+ ions. Preliminary results indicated that all the tested materials are effective in the adsorption of the tested metal ions and do not release the removed metal ions upon sinking in ultrapure water, even for a very long time. Interestingly, compressive strength tests performed before and after the washing treatments show that the foamed samples remain intact and maintain their physical–mechanical characteristics, suggesting that these kinds of materials are promising candidates for the production of self-standing, monolithic adsorbent substrates that can be easily collected when exhausted, which is a major advantage in comparison with the use of powdered adsorbents. Moreover, since these materials can be obtained by a simple and versatile experimental procedure, they could be easily shaped or directly foamed into precast molds to be used in packed beds as membranes.
Highlights
Aqueous wastes deriving from different kind of anthropic activities, such as mining or metal industries, contain high concentrations of cations of heavy metals such as Cd, Pb, Cu, Cr, Zi, and Ni.These wastes represent a serious threat to the contamination of soils and waters [1,2,3], as they accumulate in living organisms, generating serious and often lethal pathologies
In this paper, hybrid organic–inorganic geopolymeric foams were successfully used as monolithic adsorbents for the removal of metallic ions pollutants from wastewaters
The advantage in the obtainment and use of hybrid geopolymer-based materials with respect to unmodified geopolymers relies in the fact that the homogeneous combination of inorganic and organic moieties in a single-phase material provides unique possibilities to obtain properties that are not found in the organic polymer or in the inorganic materials independently
Summary
Aqueous wastes deriving from different kind of anthropic activities, such as mining or metal industries, contain high concentrations of cations of heavy metals such as Cd, Pb, Cu, Cr, Zi, and Ni.These wastes represent a serious threat to the contamination of soils and waters [1,2,3], as they accumulate in living organisms, generating serious and often lethal pathologies. The removal of heavy metal cations from the wastewater of industrial or agricultural activities, before they are released. Many effective methods for metals removal from wastewater were developed up to now, including ion exchange, chemical precipitation, electrochemical treatment, reverse osmosis, adsorption, and biosorption [4,5]. Inorganic porous materials are widely studied in the developing of membranes or high-efficiency adsorption materials [6]. In this field, great attention has been devoted to zeolites for their effectiveness in the removal of heavy metal cations from wastewater [7]. Ion exchange properties shown by these materials are due to their unique crystalline microporous structure, characterized by fixed pore dimensions that make them selectively accessible to metal cations, depending on their charge and size [8,9]
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