A systematic investigation of aluminium ion speciation at high temperature. Part. 1. Solution studies

Abstract

Speciation diagrams of aluminium ions in aqueous solution (0.2 M) at high temperature (90 degrees C) have been obtained from 48 h time-resolved multi-batch titration experiments monitored by 27Al NMR spectroscopy, potentiometry and dynamic light scattering. The quantitative speciation patterns and kinetic data obtained offer a dynamic picture of the distribution of soluble and insoluble Al species as a function of hydrolysis ratio h(h=[OH-]/[Al3+]) over a very broad range of conditions (-1.0 < or =h < or = 4.0). Monomeric, small oligomeric, tridecameric (the 'Al13-mer') and the recently characterised 30-meric aluminium species (the 'Al30-mer') as well as aluminium hydroxide have been identified and quantified. The Al13-mer species dominates over a relatively broad range of hydrolysis ratios (1.5 < or =h< or = 2.7) during the first 6 h of experiment, but are gradually replaced by Al30-mers at longer reaction times. Kinetic profiles indicate that the formation of the Al30-mer is limited by the disappearance of the Al13 species at mildly acidic conditions. The estimated rate constants of both hydrolytic processes show good internal correlation at h> or = 1.5. The effect of local perturbations leading to the formation of aluminium hydroxide below the electroneutrality point (h= 3.0) has been estimated quantitatively.

Effect of thermal treatment on the formation and transformation of Keggin Al13 and Al30 species in hydrolytic polymeric aluminum solutions

“…Although there are a few reports on Al 30 species, and a great deal of progress has been achieved, most of these investigations were carried out in diluted solutions and were aimed to structural characterization. Shafran et al [27,28] have studied the Al speciation in medium concentration at high temperature using improved 27 Al NMR quantification method. To date, much less was concerned on the formation and transformation of Al 30 species in highly concentrated HPA solutions (0.2-2.0 mol L −1 ).…”

Mechanochemical synthesis of the [Al13O4(OH)24(H2O)12]7+ Keggin ion

“…The structure of e-Al 13 is highly symmetric with a central tetrahedral fourfold coordinated Al +3 surrounded by 12 octahedral coordinated Al 3+ . The e-Al 13 is usually synthesised in an Al 3+ solution by titrating with NaOH or KOH [1][2][3][4][5][6]. Recently, the homogenous hydrolysis of Al 3+ solution by the decomposition of urea [7] and the supramolecular selfassembled methods were also used for the e-Al 13 preparations [8].…”

Study on the hydrolysis/precipitation behavior of Keggin Al13 and Al30 polymers in polyaluminum solutions

“…Al 30 , with 2 nm in length (Phillips et al, 2003), was the largest Al polycation that was identified in polyaluminum solution. Al 30 formed by further polymerizing two Al 13 and four Al monomers under hydrothermal treatment (Allouche and Taulelle, 2003;Shafran and Perry, 2005a). Al 30 species was more thermal resistant and more stable in low pH solution than Al 13 species (Chen, 2006;Chen et al, 2007).…”