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Dissolution of ilmenite and related minerals in sulphuric acid

McConnel, Stephen Robert (1978) Dissolution of ilmenite and related minerals in sulphuric acid. PhD thesis, Murdoch University.

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Abstract

A detailed study of the reaction of ilmenite and its related minerals with sulphuric acid has been made to determine the influence of chemical and physical factors upon the dissolution Such information ra te. would be useful in any ilmenite upgrading process involving sulphuric acid and may lead to a better understanding of the natural alteration of ilmenite. Thirteen natural ilmenite type minerals of differing composition ranging from 45.2 to 82.5 wt. % of TiO2, as well as synthetic ilmenite, FeTiO3, are used to study the effect on the dissolution rate of temperature. particle size, acid concentration and stirring rate.

Results of experiments using rotating discs of synthetic ilmenite and massive natural ilmenite indicate that the reaction is controlled by chemical processes at the mineral surface. The reaction rate in 9 molar sulphuric acid over the temperature range 65°C to 85°C is independent of the hydrodynamic conditions and has apparent activation energies of the order of 90- 100 kJ mol -1 The massive natural ilmenite disc displayed distinctly anisotropic behaviour, indicating the importance of twinning planes in the dissolution process.

Dissolution rates of all the ilmenite minerals, in the form of beach sand concentrate or crushed massive ore, are determined over the temperature range 65°C to 90°C in 9 molar sulphuric acid. In all cases the kinetic data shows an initial period of variable rate, dependent upon the mineral composition and structure, followed by a period of constant rate. The ratio of titanium to iron dissolution rates follows a general trend with variation in composition from sample to sample and a correlation between rate constants and the degree of alteration is observed. Further experiments using magnetically separated fractions as well as experiments in which the separate ferrous and ferric iron dissolution rates are measured, give additional information about the dissolution process.

On the basis of the observed kinetics. X-ray diffraction and optical and electron microscopy, a mechanism is proposed explaining the initial variable rates in terms of more rapid iron removal from the altered surface of the mineral, followed by dissolution of the bulk of the solid.

Since the natural weathering of ilmenite is an important process attempts are made to observe the alteration of ilmenite using chemical and electrochemical techniques. Leaching of ilmenite sand with water at 90°C for 11 months dissolves traces of iron and produces a surface coating on the grains of complex nature. Oxidation of ilmenite at 600°C followed by acid leaching removed iron preferentially and gives a product similar to that of naturally altered ilmenite. In the electrochemical studies ilmenite electrodes of both synthetic and natural material were fabricated and cyclic voltametric and controlled potential techniques were used. With both types of electrode little change is observed with anodic (oxidative) potentials but cathodic (reductive) potentials increases the dissolution rate in dilute sulphuric acid markedly, although selective removal of iron or titanium from ilmenite is not observed. Electrochemical processes may therefore play an important role in the natural weathering of ilmenite minerals.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Barton, Allan
URI: http://researchrepository.murdoch.edu.au/id/eprint/51617
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