Fluorescence spectroscopy analysis of fly ash removal from aqueous systems: adsorption of alginate to silica and alumina.

Fly ash is a toxic industrial waste, mainly consisting of silica and alumina particles, that has been found discharged into the environment. It is proposed that alginate, a naturally occurring biopolymer, can bind to these minerals and thus play a role in water purification. The binding forces involved in this process consist of weak interactions, such as van der Waals forces and electrostatic interactions. Although the attachment of alginate to mineral surfaces is mainly governed by its carboxylate groups, hydroxyl moieties could play a role in the interaction between the polymer and minerals. This work aims to use the SiO2 and Al2O3 particles as models for fly ash and to show the use of alginate biopolymers (fluorescently labelled with an aminonaphthaline sulfonate fluorophore (AmNS)) to coagulate them. The addition of simple electrolytes like NaCl and CaCl2 encourages the coiling of the polymer chain at high pH values which has an effect on its capability to bind to the inorganic particles. A combination of fluorescence and ICP-MS demonstrated that alginate has a considerable adsorption affinity for Al2O3, whereas it attracts SiO2 weakly. The adsorption process is pH dependent: strong adsorption was observed at low pH values. The dependence of adsorption on the mineral (Al2O3 and SiO2) concentration was also examined under different pH conditions: the adsorption amount was observed to increase by increasing the solid concentration. Adsorption isotherms obtained at low and high mineral concentrations were found to be Henry in type.

Fluorescence Spectroscopy Analysis of the Bacteria-Mineral Interface: Adsorption of Lipopolysaccharides to Silica and Alumina.

We present here a quantification of the sorption process and molecular conformation involved in the attachment of bacterial cell wall lipopolysaccharides (LPSs), extracted from Escherichia coli, to silica (SiO2) and alumina (Al2O3) particles. We propose that interfacial forces govern the physicochemical interactions of the bacterial cell wall with minerals in the natural environment, and the molecular conformation of LPS cell wall components depends on both the local charge at the point of binding and hydrogen bonding potential. This has an effect on bacterial adaptation to the host environment through adhesion, growth, function, and ability to form biofilms. Photophysical techniques were used to investigate adsorption of fluorescently labeled LPS onto mineral surfaces as model systems for bacterial attachment. Adsorption of macromolecules in dilute solutions was studied as a function of pH and ionic strength in the presence of alumina and silica via fluorescence, potentiometric, and mass spectrometry techniques. The effect of silica and alumina particles on bacterial growth as a function of pH was also investigated using spectrophotometry. The alumina and silica particles were used to mimic active sites on the surface of clay and soil particles, which serve as a point of attachment of bacteria in natural systems. It was found that LPS had a high adsorption affinity for Al2O3 while adsorbing weakly to SiO2 surfaces. Strong adsorption was observed at low pH for both minerals and varied with both pH and mineral concentration, likely in part due to conformational rearrangement of the LPS macromolecules. Bacterial growth was also enhanced in the presence of the particles at low pH values. This demonstrates that at a molecular level, bacterial cell wall components are able to adapt their conformation, depending on the solution pH, in order to maximize attachment to substrates and guarantee community survival.