Mandy Mende

Higher efficiency in the flocculation of clay suspensions by using combinations of oppositely charged polyelectrolytes

Abstract Dual systems—the highly charged polycation poly(diallyll-dimethyl-ammoniumchloride) (PDADMAC) in combination with different high molecular weight polyanions of the polyacrylamide type—were tested as flocculants for clay suspensions and natural waste waters from gravel pits. The flocculant performance was characterised by measuring the sedimentation behaviour as well as the residual turbidities and the extent of polymer adsorption. Whereas the molecular weight of the high molecular weight polycation is of lower influence, the removel of suspended particles is greatly affected by the molecular weight of the polyanion. Our experiments showed that degradation of the very high molecular weight polyanions leads to higher turbidity of the supernatant. The order of addition of the two polyelectrolytes influences the flocculation mechanism. Most effective is the addition of polycation followed by the polyanion. So a combination of patching and bridging is obtained.

Application Relevant Characterization of Aqueous Silica Nanodispersions

This work describes the application relevant characterization of eight commercially available silica powders dependent on dispersing procedure using different instruments: photon correlation spectroscopy, nitrogen adsorption, and particle charge detector. The particle size of silica was found to be different in dispersion from that of all types of fumed silica, where, after proper dispersion, the measured average particle size is similar and much higher than the primary particle size. The different properties of these two silica types will be discussed.

The Influence of Salt Anions on Heavy Metal Ion Adsorption on the Example of Nickel

The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.

The influence of cations on the dissociation behaviour of copolymers of propene and maleic acid and their modified products with taurine in salt-free solution

Potentiometric and conductometric titrations were used to study the dissociation behaviour of poly(propene-co-maleic acid) and poly(propene-co-maleic acid) modified with various contents of taurine (2-aminoethanesulfonic acid) in salt-free solution. Copolymers of propene and maleic acid with different molecular weights were titrated with LiOH, NaOH, and KOH. The influence of molecular weight on pKa is ascertainable in both the first and second dissociation step. Of the various alkali metal cations studied, lithium had the most significant effect on the dissociation behaviour. The acidic strength decreased in the order lithium > sodium ≥ potassium. After insertion of sulfonic acid groups into poly(propene-co-maleic acid), the influence of strong acidic groups on the dissociation behaviour of carboxylic groups was studied. The contents of taurine were 10, 25, and 50 mol%. The second dissociation step was analyzed in this case. The pKa values increased with increasing content of taurine for titrations with LiOH and KOH, but not NaOH. When NaOH was used, the pKa decreases if the polymer was modified with 10% taurine. Higher taurine contents had no influence on the magnitude of pKa. The results demonstrate the strong influence of short-range electrostatic interactions on the dissociation behaviour of weak polyacids.