|dc.description.abstract||This thesis involves the design, synthesis and testing of organic hydrophobic
ligands. They would act as co-collectors in froth flotation processes to enhance the
recovery of sulfidic minerals which have undergone some oxidation on processing
and are not efficiently collected by the commercial reagents used in froth flotation.
Strong and selective binding to iron(III) oxide/hydroxide surfaces, e.g. goethite, over
unwanted silicaceous material was considered essential criteria for such new cocollectors.
A general overview of froth flotation processes is given in Chapter 1 as well
as a description of the analytical techniques used in this thesis and the features that
the ligands must have to act as co-collectors.
On the basis of the strong binding to iron(III) surfaces of the organic ligand
Irgacor 419®, used commercially as a corrosion inhibitor for iron, this compound was
studied as a potential co-collector. Adsorption isotherms were determined by UV-Vis
spectroscopy for two carboxylic acids that may also bind strongly to goethite, the
results of which are discussed in Chapter 2.
Chapter 3 involves the measurement of the strength of binding of one the
most widely used type of collectors for sulfide ores, potassium ethyl xanthate.
Complications in the analysis of materials in solution by both ICP-OES and UV-Vis
spectroscopy arose due to the instability of potassium ethyl xanthate in solution,
making determination and interpretation of isotherms difficult. The determination of
adsorption isotherms for 2-mercaptobenzothiazole, which showed weak binding to
goethite as well as to silica, and the mode of binding of 2-mercaptobenzothiazole on
copper(I) surfaces is reported in Chapter 4. A crystal structure was obtained in which
four units of 2-mercaptobenzothiazole bridge two nickel atoms through the nitrogen
atom and the exocyclic sulfur and is considered as a model for binding to sulfidic
Chapter 5 looks at the strength of binding to goethite and silica of various
hydroxamic acids. Benzohydroxamic acid was initially selected for study since
hydroxamates are known to act as collectors for oxidized materials. Unpredictably,
benzohydroxamic acid showed strong binding to a goethite surface and did not
release any iron from the surface into solution, which would have been predicted due
to its known strong chelating abilities to iron(III). The X-ray structure determination
of the first example of a dinuclear Fe(III) hydroxamate complex showed this to have
-oxo bridge formed by the hydroxamate unit and supports multisite attachment
between this ligand and the surface, as suggested by adsoption isotherms. Simple
models based on this dinucleating motif provide plausible modes of multisite
attachment to a goethite surface. Competitive binding studies provided a way of
ranking the ability to bind to goethite of acetohydroxamic acid, which was not
suitable for analyses by either ICP-OES or UV-Vis spectroscopy. Of the ligands
studied in this chapter acetohydroxamic acid was found to bind most strongly to
goethite followed by benzohydroxamic acid. In Chapter 6, the attachment to goethite
and silica of a series of phosphonic acids is investigated. All show a very high
binding strength to goethite.
Froth flotation experiments at a laboratory scale are described in Chapter 7.
The types of ligand that showed strong binding to goethite in adsorption isotherms
experiments were tested as co-collectors in different ores and conditions. There is not
a simple correlation between adsorption isotherm data and flotation performance as
co-collectors because other factors, besides strength of binding, affect the system.
Benzohydroxamic acid was the ligand that increased the grade/recovery of the
process in all the cases studied. Irgacor 419® enhances the grade/recovery curve for
Palabora ore and phenyl malonic acid for Kennecott ore. These results support the
original proposition that it may be possible to increase the recovery of oxidized
particles substantially by using a blend of collectors which includes a compound to
target the oxidized sites.||en