Davor Kovačević

The adsorption of lead species on goethite

Adsorption of lead ionic species at the goethite aqueous interface, as well as the electrokinetic properties of the system, were measured as a function of pH. The interpretation was based on the Surface Complexation Model assuming that association of lead species with negatively charged surface sites takes place. The electrostatic potential affecting the state of the surface species was obtained from the electrokinetic potential by Gouy-Chapman theory introducing the electrokinetic slipping plane as an adjustable parameter. It was found that singly charged lead species (PbOH+) are bound to negatively charged surface sites with the equilibrium adsorption constant logKa = 14 ą 0.2. The capacitance of the Helmholtz layer was found to be C1 = 0.4 ą 0.1 F m-2. These findings were confirmed by employing the standard triple layer model (TLM).

Effect of Corrosion on the Isoelectric Point of Stainless Steel

Abstract The recently developed adhesion method for determining the isoelectric points (IEP) of conductive metal surfaces was applied in studying the corrosion processes of stainless steel (SS). This technique allowed for characterization of the charge on the metal oxide surface as a function of pH. The magnitude of IEP was found to correlate with the structure of the oxide layer. The exposure of SS to air at 1,000°C reduced the original pHIEP from 4.15 to 2.8 as a result of the presence of magnetite. Treatment at lower temperatures yielded a significant portion of hematite in the oxide layer and pHIEP shifted to 3.3. The corrosion of SS in aqueous sodium chloride (NaCl) solution at room temperature, as examined by the proposed electrokinetic method, resulted in the formation of magnetite in the early stage of the process, while hematite and/or lepidocrocite was detected as a final product.

Chapter 6 – Thermodynamics of the solid/liquid interface - its application to adsorption and colloid stability

This chapter discusses thermodynamics of the solid/liquid interface and its application to adsorption and colloid stability. Charging of solid surfaces in liquid medium is a consequence of interactions of ions from the bulk of the solution with surface groups. Surface charge determines the distribution of ions in the liquid layer near the surface. Electrostatic interactions between charged particles are responsible for the stability of colloid dispersions—that is, the rate of particle aggregation depends on the equilibrium in the electrical interfacial layer (EIL) located between solid and liquid medium. It is shown that the colloid stability caused by electrostatic repulsion among particles is determined by the electrostatic potential at the onset of the diffuse layer and the distribution of ions within the diffuse layer. To understand the colloid stability phenomena, one should consider the equilibrium at solid/liquid interface. Interfacial reactions are considered by surface complexation model (SCM) and corresponding interfacial equilibrium constants. There are different theoretical models describing the structure of EIL differing in the quantitative relationships between electrostatic potentials and surface charge densities. Theoretical interpretation of experimental data depends on the choice of the employed model. The most frequently investigated aqueous dispersions are those the surface charge of which depends on pH, such as metal oxides and hydroxides. In the derivation of the activity coefficients of interfacial species, it will be assumed that the major contribution to the non-ideality is because of the electrostatic effects. The reason for such a simplification is that electrostatics plays a major role.

Selective immobilization of Acinetobacter junii on the natural zeolitized tuff in municipal wastewater

The immobilization of desired bacteria onto material was usually performed in synthetic media. The aim of this study was to test the immobilization of phosphate (P)-accumulating bacteria Acinetobacter junii onto natural zeolitized tuff (NZ) in the raw or sterilized municipal wastewater containing the common bacteria Escherichia coli and Enterococcus faecalis and the performance of immobilized A. junii in the same type of wastewater. In the sterilized wastewater which contained the mixture of A. junii, E. coli and E. faecalis, the A. junii was selectively immobilized onto NZ in significantly higher numbers than E. coli and E. faecalis. The A. junii added in the form of bioparticles to the wastewater containing E. coli and E. faecalis, multiplied and removed P from wastewater. The P removal from wastewater was a function of biomass of P-accumulating bacteria and not the amount of NZ or bioparticles used. The performance of A. junii was significantly better in membrane filtered than in autoclaved wastewater. The experiments that were performed in raw non sterilized wastewater showed that A. junii can be successfully immobilized onto NZ in competition with natively present heterotrophic bacteria, retain its metabolic activity and successfully remove P from such water, which makes this technology feasible from biotechnological aspect.

Experimental and theoretical study of the silica particle interactions in the presence of multivalent rod-like ions.

The silica particle interactions in the presence of spermidine were systematically investigated both from experimental and theoretical points of view. The hydrodynamic radii and the corresponding polydispersity indices of the colloidal silica particles were determined by dynamic light scattering (DLS) as a function of spermidine concentration. Whereas the effective size of the silica particles increases with increasing spermidine concentration (pointing to the particle aggregation), the polydispersity index first increases reaches a maximum and then further decreases with the increasing spermidine concentration. From the mobility measurements it was concluded that the increase in spermidine concentration causes less negative values of zeta potential, meaning that the adsorption of spermidine leads to the less negative silica surface. Moreover, Monte Carlo (MC) simulations also confirmed that the addition of spermidine reduces the repulsion between silica particles. The MC concentration profiles of spermidine close to the charged silica particle are in a very good agreement with the results obtained by theory. An important motivation for our study is the effectiveness of multivalent ions to coagulate colloidal suspensions; e.g., the multivalent ions are exploited in the water purification process.

Three routes to nickel(II) salicylaldehyde 4-phenyl and 4-methylthiosemicarbazonato complexes: mechanochemical, electrochemical and conventional approach

In the synthesis of Ni(II) salicylaldehyde 4-phenyl and 4-methyl-thiosemicarbazonato complexes conventional, electrochemical and mechanochemical routes were applied and compared. Polynuclear tetrahedral [Ni(sal 4-Metsc)]n (1) and mononuclear square planar [Ni(sal 4-Phtsc)(H2sal 4-Phtsc)]·CH3OH (2) were obtained by the conventional method. The electrochemical synthesis proved to be a simple and efficient route for the synthesis of brownish-red single crystals of square planar (2) and polycrystalline green octahedral [Ni(Hsal 4-Metsc)2]·(3) complexes, while the liquid-assisted mechanochemical synthesis was a fast route for the synthesis of green octahedral [Ni(Hsal 4-Metsc)2]·(3) and [Ni(Hsal 4-Phtsc)2]·(4). The advantages and disadvantages of all used synthetic methods were discussed. The characterization of square planar (2) and two octahedral complexes (3) and (4) was performed by X-ray diffraction methods, infrared and NMR spectroscopy. In addition quantum chemical calculations were performed for CS (conformer which enables O–H⋯S intramolecular hydrogen bond formation in 2-hydroxyaryl Schiff base thiosemicarbazones) and SC (conformer with the thiocarbonyl group turned away from O–H⋯N intramolecular hydrogen bond) forms of both ligands and in each case the CS conformer was lower in energy.

Adsorption of Oxalic Acid onto Hematite: Application of Surface Potential Measurements

The surface potential at the hematite/aqueous oxalic acid interface was measured by means of a hematite Single Crystal Electrode. This allowed the simultaneous interpretation of the surface potential, electrokinetic potential and adsorption data for the adsorption of oxalic acid onto a hematite surface. Based on the Surface Complexation Model, this interpretation suggested that the oxalate ion is bound to a metal ion at the solid surface to form a singly-charged oxalate-surface complex, with the charge being exposed to the potential at the outer Helmholtz layer. A number of equilibrium parameters describing the interfacial equilibrium were obtained. Thus, for the two protonation steps of the surface sites, the thermodynamic equilibrium constants were log K1 = 7.1 ± 0.4 and log K2 = 5.2 ± 0.4, respectively. Two assumptions were tested with regard to the adsorption equilibrium constant, i.e. the charge of the surface complex is exposed to the inner surface potential, ψ0, or to the outer surface potential, ψd. The constancy of the interfacial equilibrium constants led to the conclusion the latter assumption was the more appropriate. The observed value of the adsorption equilibrium constant was log Kads = 3.0 ± 0.8. It was shown that measurement of the surface potential by Single Crystal Electrodes is a helpful tool in elucidating the equilibrium behaviour of the complex at the interface.

Binding of cadmium at the goethite aqueous interface

The adsorption of cadmium ionic species at the goethite aqueous interface was measured as a function of pH. The electrokinetic properties of the system were also investigated. The surface complexation model was used for interpretation, and the association of cadmium species with negatively charged surface sites was considered. The electrostatic potential affecting the state of the surface species was calculated from the electrokinetic potential by Gouy-Chapman theory introducing the electrokinetic plane separation as an adjustable parameter. It was found that singly charged cadmium species are adsorbed on negatively charged surface sites with the corresponding equilibrium adsorption constant log K = 13.3 ± 0.35. The capacitance of the Helmholtz layer was found to be between 2 and 2.5 F m−2.

Adsorption of bovine serum albumin on previously formed PAH/PSS multilayer: a stagnation point optical reflectometry study.

The method of stagnation point optical reflectometry was applied for investigation of adsorption of bovine serum albumin (BSA) on previously formed poly(allylamine hydrochloride)/poly(sodium 4-styrenesulphonate) (PAH/PSS) multilayer with PAH being a terminal layer. The solid substrate was silica in the form of silicon wafers carrying an oxide layer. In order to interpret the adsorption of BSA, the build-up mechanism of PAH/PSS multilayers was examined with special emphasis on the effect of electrolyte concentration, pH of solution, and the anchoring (precursor) layer on that process. Additionally, the effect of BSA concentration and of the anchoring layer on BSA adsorption was investigated. It was shown that in all investigated systems the adsorption of BSA depends on conditions under which the multilayer was formed (ionic strength, pH and presence of an anchoring layer), as well as on BSA concentration. It follows that adsorption of BSA could be controlled not only by choosing suitable BSA concentration, but also by modifying the preformed multilayer.

Alkaline disinfection of urban wastewater and landfill leachate by wood fly ash

Abstract Wood fly ash is an industrial by-product of the combustion of different wood materials and is mostly disposed of as waste on landfills. In our preliminary experiments, wood ash exhibited antibacterial activity against urban wastewater bacteria and we focused on wood fly ash as a potential substrate for wastewater disinfection. The addition of ash at a concentration of 10 g L-1 (1 %) caused an instant increase of pH in urban wastewater and landfill leachate. High pH (10.1-12.7) inactivated bacterial populations in the wastewater and the removal of faecal coliforms and intestinal enterococci after 6 h of contact was 100 % (below the detection limit; <1 CFU per mL) with the most efficient ash sample (ash from combustion of beech) both in urban wastewater and landfill leachate. Properly chosen wood fly ash, i.e. one that tends to increase the pH to the greatest extent, proved to be a very effective disinfection substrate. Considering that water treated with wood ash has a high pH and needs to be neutralised before discharge, ash would be suitable for disinfection of leachates when smaller volumes are treated Sažetak Leteći pepeo iz drvne industrije je nusproizvod koji nastaje spaljivanjem različitog drvnog materijala i većinom završi na odlagalištima otpada. Budući da je u preliminarnim ispitivanjima leteći pepeo pokazao antibakterijsko djelovanje prema bakterijama iz otpadne vode, pokusi su usmjereni istraživanju pepela kao potencijalnog supstrata za dezinfekciju otpadne vode. Dodatak pepela u koncentraciji od 10 g L-1 (1 %) uzrokovao je trenutno povećanje vrijednosti pH komunalne i procjedne otpadne vode s odlagališta otpada. Visoki pH (10,1-12,7) uništio je bakterije u otpadnoj vodi te je korištenjem najučinkovitijega pepela (dobivenog spaljivanjem bukve) postignuto 100-postotno uklanjanje (odnosno manje od mogućnosti detekcije; <1 CFU mL-1) fekalnih koliforma i crijevnih enterokoka iz komunalne i procjedne otpadne vode nakon šest sati kontakta. Odgovarajući pepeo, odnosno onaj koji uzrokuje najveće povećanje vrijednosti pH, pokazao se kao vrlo učinkovit supstrat za dezinfekciju. Uzimajući u obzir činjenicu da otpadna voda tretirana pepelom ima povišen pH, te da je vrijednost pH potrebno neutralizirati prije ispuštanja u prirodni prijemnik, leteći drvni pepeo bio bi pogodan za dezinfekciju procjedne otpadne vode zbog manjih volumena koji zahtijevaju obradu