A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties

Abstract

ROBERT C. TURNER. Can. J. Chem. 54,1910Chem. 54, (1976.When a solution of A1(CI04)3 or AICI, with total Al concentration between 5 X 10-4 and 6 X 1 0 -W is partially neutralized very slowly with a base, it is possible to produce a solution of polynuclear hydroxyaluminum cations with no solid phases present. When such a solution is aged, the polynuclear hydroxyaluminum cations, Alpl, disappear very slowly at 25 "C and a second type of polynuclear hydroxyaluminum cations, Alp-,, is formed. The second type, Alpz, has some properties that are the same as those of Alp1, e.g. they both have an OH/A1 mole ratio equal to or very nearly equal to 2.5, diffuse readily across a dialysis membrane, and are removed from solution by the clay mineral bentonite in an exchangeable form. Some of their properties, however, are entirely different, e.g. AIpI reacts with 8-hydroxyquinoline about 250 times faster with a much lower energy of activation than does Alp,, is much less resistant to attack by HC1, and is precipitated at a p H about 0.5 p H units lower than Alpz. The transformation of AlPI to Alpz is a first order process with an energy of activation of 20.8 kcal per mol. The specific rate constant seems to be affected somewhat by the extraneous anion present and the degree of neutralization; experimental values varied from 0.57 X 10-3 to 3.5 X 10-3 day-1 at 25 "C.

Mechanisms of Gibbsite Crystallization from Partially Neutralized Aluminum Chloride Solutions

“…Because solution pH only slightly decreased, whereas the concentration of monomeric A1 remained nearly the same, the basicities and the thermodynamic dissociation constants for the unstable and stable polymers should have been similar. That the unstable and stable OH-AI polymers were similar in basicity was reported earlier (Turner, 1976a(Turner, , 1976bHsu, 1984, 1985). An exact mechanism for the unstable-stable polymer transformation cannot be proposed on the basis of the results currently available, but this mechanism most likely involves internal structural arrangement.…”

Reaction of OH-Al Polymers with Smectites and Vermiculites

“…In general, OH-AI solutions freshly prepared by partially neutralizing an A1 salt solution with a base are dominated by rapid-reacting polymers that gradually convert to slow-reacting species with time (Turner, 1976a(Turner, , 1976bHsu, 1984, 1985;Denney and Hsu, 1986;Hsu, 1988). It has been suggested (Denney and Hsu, 1986;Hsu, 1988Hsu, , 1989) that only rapidreacting OH-AI polymers are of All 3 Keggin structure, but the slow-reacting polymers are of Al(OH)3-fragment structure.…”

“…Hsu and his colleagues Hsu, 1984, 1985;Denney and Hsu, 1986;Hsu, 1989) postulated that both of these two proposed polymers were present in OH-AI solutions. Both of them reacted with hydroxyquinoline (Turner, 1976a(Turner, , 1976b or ferron Hsu, 1984, 1985) following a pseudo-firstorder reaction, but their rate constants differed by some 250 times. They formed distinctly different basic Al sulfates upon the addition of Na2SO4 Hsu, 1984, 1985) and are very different in resistance to acid (Turner, 1976b;Hsu, 1988).…”

Determination of Polymeric Aluminum in Soil Extracted with a Modified Anion-Exchange Resin as a Solid-Phase Adsorbent by ICP-AES

“…1 However, some investigations have indicated that the polymeric Al species obtained from an 27 Al-NMR analysis are in good accordance with the results obtained from Ferron timed-photometry. All the polymeric Al species exist in cationic forms, [16][17][18][19][20][21] and most of them are considered to be Al13. Therefore, an Al13 standard can be used to stand for the total polymeric Al fraction under most conditions.…”