Charakterisierung von Al(III)‐Spezies in basischen Aluminiumchlorid‐Flockungsmitteln mittels Ferronreaktion bzw. ²⁷Al‐Kernresonanzspektroskopie Characterization of Al(III) Species in Basic Aluminium Chloride Flocculants by Means of Ferron Method and ²⁷ Al Nuclear Magnetic Resonance

Abstract

Summary: Flocculant processes as a treatment step in water and wastewater purification technology are of increasing importance. Partially neutralized aqueous aluminium chloride solutions -the basic aluminium chlorides -are often used as flocculants in water conditioning. The present paper describes the reactions which appear in these solutions by their dilution, the identification of occurring cationic aluminium species, and the relations between the composition of the solutions and their efficiency as flocculants. The solutions were quantitatively analyzed using 27A1 NMR and the ferron method; the latter method offers a simple and inexpensive alternative for identification and quantification of aluminium cations and can facilitate investigations of the A1 speciation at concentrations too low for analysis by NMR. The distribution of aluminium cations in basic aluminium chloride solutions changes drastically by the dilution while applied as flocculants because the equilibrium strongly depends on the concentration. The dynamic changes following the dilution of partially neutralized solutions were investigated simply by mixing a solution with water and immediate analysis by the ferron method. It could be shown that rearrangement reactions occur in the system, partially overlapping each other; the oligomeric cations seem to be especially instable. Furthermore, a partial change from octahedral to tetrahedral coordination of the aluminium in the species can be observed. At extremely low aluminium concentration5 as in the case of application of the basic aluminium chloride solutions for flocculation, monomeric and especially transition polymeric and polymeric aluminium cations, respectively, appear. The ratio of these cations to each other also depends on the time up to the flocculation. Accordingly, these cations especially the different polymeric aluminium species seem to be important for the efficiency of the basic aluminium chlorides as flocculants in water conditioning.

Large Aqueous Aluminum Hydroxide Molecules

“…The polyoxocations are also present in catalysts and clay-pillaring agents [e.g., refs −11] and in water-treatment plants. We add them to water to eliminate organic macromolecules and metal pollutants [e.g., refs and ], and these aluminum hydroxide molecules are not too different from some vaccine adjuvants that we inject into ourselves [e.g., refs and ].…”

Single Ion and Dimerization Studies of the Al(III) Ion in Aqueous Solution

“…3+ and the tetrahedral Al(OH) 4 ions in solution (which form at low and high pH values, respectively) have been studied extensively using both experimental and theoretical techniques. [17][18][19][20] It is known that the octahedral Al(H 2 O) 6 3+ ion undergoes hydrolysis through deprotonation and produces Al ion species with smaller coordination numbers with an increasing pH value. In general, the hexa-coordinated Al(III) species (including different hydrolysis products in hexa-coordinated arrangements) have been widely studied using theoretical chemistry tools.…”

“…The geometry of hydrated metal ions has usually been investigated using static first principles calculations in the gas phase and/or in aqueous solution using a continuum model for water. − Even though these theoretical studies can provide important information, they do not capture the impact of the solution dynamics nor the impact of intermolecular hydrogen bonding interactions in bulk solution on the predicted geometries of metal ions. Specifically, the structures of the octahedral Al(H 2 O) 6 3+ and the tetrahedral Al(OH) 4 − ions in solution (which form at low and high pH values, respectively) have been studied extensively using both experimental and theoretical techniques. − It is known that the octahedral Al(H 2 O) 6 3+ ion undergoes hydrolysis through deprotonation and produces Al ion species with smaller coordination numbers with an increasing pH value. In general, the hexa-coordinated Al(III) species (including different hydrolysis products in hexa-coordinated arrangements) have been widely studied using theoretical chemistry tools. , In fact, theoretical studies have been performed using the hexa-coordinated Al(H 2 O) 6 3+ , Al(OH)(H 2 O) 5 2+ , and Al(OH) 2 (H 2 O) 4 + geometries either in the gas phase or in aqueous solution utilizing a continuum model for water.…”

The static anion exchange method for generation of high purity aluminium polyoxocations and monodisperse aluminium hydroxide nanoparticles

“…This task can be achieved, first of all, by the dynamic quantitative monitoring of Al speciation, examples of which have been reported in the previous publications of our group [14][15][16] and other authors. [17][18][19][20] Systematic studies of Al ion speciation at room temperature 14 and at high temperature 15,16 have been conducted in order to elucidate the optimum conditions for the formation of different Al polynuclear species including the Keggin ions Al 13 and Al 30 .…”