The influence of a smectite clay on the hydrolysis of iron(III)

• Published in: Colloids and surfaces 1991-11, Vol.60, p.369-398
• Main Authors: Thompson, Dudley W., Tahir, Norhayati Mohd
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena
• ISSN: 0166-6622; 1873-4340
• DOI: 10.1016/0166-6622(91)80288-Y

The hydrolysis and precipitation of Fe(III) in simple inorganic electrolyte solutions and in aqueous dispersions of the clay mineral montmorillonite have been investigated by UV-absorption spectrophotometry, pH-titration, chemical analysis, electron microscopy, electron-probe microanalysis and microelectrophoresis. Experimental evidence indicates that during the neutralization of acid-Fe(III) solutions in perchlorate, nitrate, chloride and sulphate media, Fe(III) speciation is essentially confined to the simple hexa-aquo ion Fe 3+, the first hydrolysis product, FeOH 2+, and the 1:1 complex species FeCl 2+ and FeSO + 4. Thermodynamically irreversible precipitation appears to occur in these systems under well-defined solution conditions, yielding compounds which conform to the stoichiometry Fe(OH) x A (3- x)/ n where the value of x depends on the identity of the anion species A n− . The presence of sulphate at SO 2− 4/Fe(III) mole ratios > 1 increases the pH value required for the onset of precipitation owing to formation of the relatively stable complex FeSO + 4. Formation function data have been compared with previously proposed hydrolysis/precipitation mechanisms. In the presence of montmorillonite, hydrolysis of Fe(III) is promoted, prior to precipitation, owing to preferential adsorption of FeOH 2+ at the clay surface. Whilst the presence of the clay appears to have no significant influence on the conditions required for hydrous oxide precipitation, experimental evidence shows a marked effect of the clay are the stoichiometry and growth of the initially precipitated Fe(III) phase.