Synthesis of composite by application of mixed Fe, Mg (hydr)oxides coatings onto bentonite--a use for the removal of Pb(II) from water.

The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles in aqueous suspension and subsequent thermal treatment of the solid phase at 498 K. Structural and textural modifications of montmorillonite which occurred during the synthesis of composite were confirmed by XRD technique and N(2) adsorption at 77K. The composite structure was found to be less ordered, while its specific surface area was about two times higher than the specific surface area of the starting/native bentonite. The effectiveness of the composite in Pb(II) removal from aqueous solutions at different initial concentrations, pH and ionic strengths of the solutions was examined. The equilibrium adsorption data were analyzed using three widely applied isotherms: Langmuir, Freundlich and Dubinin-Radushkevich. The composite effectively removes both ionic and colloidal forms of Pb(II) from water and the maximum adsorption capacity obtained from the Langmuir equation was 95.88 mg/g. The main mechanisms of Pb(II) removal at low pH values were ion-exchange and outer-sphere surface complexation.

The disinfection of water by microalloyed aluminium-based composite.

In the submitted paper the water disinfection capacity of the microalloyed aluminium based composite (MABC) was studied. MABC is material in the form of steel wire, plated with microalloyed aluminium. The effects of the composite are based on the very negative stationary potential of microalloyed aluminium, and its spontaneous dissolution in water with generation of AI(III) ions, and reduction of water with the generation of H2 and OH ions. As a final product of these reactions, a voluminous Al(OH)3 precipitate is formed. Having in mind its great efficacy in purification of different waters from many chemical pollutants we made the following hypothesis: reduction characteristics of the MABC surface, presence of Al(III) and OH ions, and coprecipitation on Al(OH)3, can be also toxic and destructive for bacteria in water. The experiments were carried out with the water model solutions (WMS) based on adapted natural surface water (NSW), inoculated with the Escherichia coli. All treatments were performed in the original semi-flow system (SFS), in which convection increases efficacy. The results show that approximately every 10 min the number of viable bacteria was reduced for about one log10 count, with the complete disinfected water phase as the outcome of the treatment. At the end of the treatment, the Al(OH)3 precipitate still contained a low amount of coprecipitated viable bacteria, which died within a relatively short period.

The comparison of aluminium effects and its uptake by Escherichia coli in different media.

The investigation of the toxic effects and the uptake of aluminium by Escherichia coli in growth medium (GM) and in physiological solution (PS) have been studied. The toxicity was quantitatively determined according to the decrease of the colony forming units (CFU) in the physiological solution, that is its growth inhibition in the growth medium, vs. the aluminium concentration and incubation time, at pH 5.2, 6.2 and 7.2. The uptake of aluminium was investigated by determining the intracellular aluminium in dry weights (DW), by graphite fumace atomic absorption spectrophotometry, considering that aluminium adsorbed to the cell surface was removed by washing with EDTA solution. The results show that toxicity and accumulation increase with the increase of the aluminium concentration and incubation time. However, the linearity of these functions was lost at higher values, which indicate dependence on time and concentration saturation. The effect of pH was specific, and correlated with the form of aluminium in solution. The increase in toxicity as the pH decreases, suggests that the Al(H2O)6(3+) ion is the major toxic form, among the remaining present ones aluminium in aqueous media. The results also show that the aluminium in a concentration range from 0.10 to 10.0 mg/l toxic to E. coli in PS, was significantly less toxic for bacteria in the GM, mainly because of living conditions and the accessibility of free Al.