Note: Descriptions are shown in the official language in which they were submitted.
WO 95/08004 PCT/AU~ ce~
~169947
TITLE: "ILMENITE PROCESSING USING COLD MILLING"
Technical Field
This invention concerns the treatment of minerals
contA; ni ng titanium dioxide and iron, which are generally
called titaniferous minerals. The most common of these
minerals is ilmenite. More particularly, this invention
concerns cold milling of particulate titaniferous minerals
to form nanostructured products from which the iron content
(or a significant amount of the iron content) of the
mineral can be Lc...oved by a leaching process.
r-.-L.J.G~.d to the Invention
Ilmenite, FeTiO3, and titaniferous minerals generally, are
relatively inert minerals that have long been a major
source of titanium dioxide, TiO2, which is used as a white
pigment in paints, to produce welding rods, and in the
cosmetic and ceramics industries. Extraction of the iron
from the ilmenite and other titaniferous minerals has been,
and still is, an expensive undertaking.
Most of the currently used metallurgical processing of
ilmenite includes hot acid l~ch;ng of the particulate
mineral, with associated environmental problems. For
example, the "sulphate route" for the extraction of
titanium dioxide from ilmenite involves the steps of
(a) mixing dry milled ilmenite with 85 to 92 per cent
sulphuric acid;
(b) heating the mixture of ground ilmenite and sulphuric
acid to a temperature of about 160C, at which
temperature an exothermic reaction is initiated, the
W095/08004 21 6 9 9 ~ 7 - PCT/AU94/00550
product of this reaction being a mixture of ferrous,
ferric and titanium sulphates;
(c) forming an aqueous (or weakly acid) solution of the
mixture of sulphates, then reducing the ferric
sulphate to ferrous sulphate with scrap iron;
(d) clarifying the solution by sedimentation;
(e) removing the iron in the solution by crystA~lisation
(as FeSO4.7HzO); and
(f) extracting the titanium dioxide using hydrolysis.
Another technique that is used to process ilmenite is the
so-called "chloride route", which involves the chlorination
of impure rutile using gaseous chlorine at a temperature in
the range of from 650C to 1,150C to form titanium
tetrachloride (TiCl~). The TiCl~ is then oxidised to
produce pure titanium dioxide.
The "Rech~r" process is also used to upgrade ilmenite - to
remove iron and provide a feedstock for the "chloride
route". In the RPrhPr process, ilmenite is reacted with
coal and sulphur in an iron reduction kiln at 1100C. This
reaction reduces the iron in the ilmenite to the metallic
form. After cooling the products of the reaction, the iron
is rusted out in slurry form with ammonium chloride acting
as a catalyst for the rusting. The remai ni ~g iron
compounds are removed by 1P~.h; ng with sulphuric acid.
One of the more promising alternative ilmenite processing
methods, developed jointly by Commonwealth Scientific and
Industrial Research Organisation and Murphyores Pty
Limited, known as the "Murso process", is described in the
W095t08004 21 ~ ~ ~ 4 7 PCT/AU94/00550
specification of Australian patent No 416,143. The Murso
process uses an oxidation of the ilmenite to convert
substantially all the iron to the ferric state, then
reduction of the oxidised material to convert substantially
all the ferric iron to the ferrous state. These steps, of
oxidation of the ilmenite followed by its reduction,
produce a material which has an e~Ance~ reactivity, from
which the iron can be leached with dilute hydrochloric
acid. The cost of using hydrogen as the reducing agent and
the cost of regeneration of the hydrochloric acid used for
l~Ach;ng have made the adoption of the Murso process
commercially unattractive. Several attempts have been made
to modify the Murso process to improve its economics, but
at the time of writing this specification, it has not been
adopted commercially.
The search for other improved methods of producing rutile
from ilmenite has continued.
Disclosure of the Present Invention
The prime object of the present invention is to provide a
method of treating ilmenite and other titaniferous minerals
to convert such minerals into a form from which the iron
content can be removed by a simple leaching process.
This ob;ective is achieved by a cold milling process.
Ball milling of ores, with and without additives to
facilitate the comminution process (the reduction of
particle size) is not new. The early potential of ball
milling for the reduction and extraction of ores, however,
W O 95108004 PCTIAU94100550
216~9~!~
has generally not been fulfilled, and interest in such ore
processing technology has waned. The development of a new
form of high energy ball mill at The Australian National
University, and the success that has been achieved in
mec~nical alloying work with that ball mill (see, for
example, the specifications of International Patent
Applications Nos PCT/AU91/00248, PCT/AU92/00073 and
PCT/AU94/00057), have stimulated new interest in the cold
milling of ores. That new ball mill, which is described in
the specification of International patent application
No PCT/AU90/00471 (WIP0 Publication No W0 91/04810),
enables controlled-energy milling of a charge to be
effected. The present inventors have now discovered that
under certain milling conditions, ilmenite can be reduced
while being converted into a nanostructural form, and that
iron can be removed from this product (for example, using
hydrochloric acid at a temperature of about 100C).
The basic requirements of the cold milling process are:
(i) that high energy milling is carried out at room
temperature for a sufficient time period (up to 300 hours)
to produce a powder having a nanostructural form, and
(ii) that the milling is effected in the presence of
suitable additives to the ball mill charge.
Thus, according to the present invention, there is provided
a method of treatment of a titaniferous ore to facilitate
the removal of iron from the ore to produce rutile, the
method comprising high energy milling of the ore in
particulate form in the presence of a suitable additive for
a period sufficient to form a nanostructural titaniferous
product.
WO95/08004 PCT/AU94/00550
~1699~7 ~
The additives include both solid and liquid reducing
agents. Amorphous boron has been found to be a useful
additive, as have a range of surfactants and organic
materials (particularly long chained hydrocarbons). Among
the surfactants which may constitute the additive of the
present invention are:
(a) ~ heYa~ecyl dimethyl ammonium acetate (DHDAA);
(b) didodecyl dimethyl ammonium bromide (DDAB);
(c) didodecyl dimethyl ammonium acetate (DDAA);
(d) didodecyl dimethyl ammonium hydroxide (DDAOH); and
(e) sodium didodecyl sulphate (SDDS) - an anionic double
~.h~; ne~ surfactant.
noAec~ne is a preferred long chained hydrocarbon which can
be used as the additive of this invention.
To extend this method to include the production of rutile,
the milled ore must subsequently be l~che~ to extract the
iron from it (for example, using hydrochloric acid at a
temperature of about 100C).
Preferably the milling is carried out in a ball mill of the
type described and claimed in the specification of
International patent application No PCT/AU90/00471.
A better understanding of the present invention will be
obtained from the following description and discussion of
experimental work in connection with the cold milling of
- 25 ilmenite, which has been undertaken by the present
inventors.
W O 95/08004 PCT/A U94/00550
~169947
-- 6 --
Description of Cold Milling Work
The present inventors hypothesised that subjecting a
particulate titaniferous material to prolonged milling
should change the mineral into a reactive nanostructural
form, from which it should be possible to remove a-Fe by
acid leaching or by magnetic separation. When this
hypothesis was tested, simple milling of ilmenite did not
produce a reactive nanostructural form of the mineral.
However, milling ilmenite with an additive to the ball mill
charge, surprisingly, did yield a reactive nanostructural
product.
A series of experiments were then performed with ilmenite
(in its mineral sand form) to investigate this phenomenon
further. In each experiment, the particulate ilmenite was
subjected to prolonged high-energy milling in a ball mill
of the type described in the specification of International
patent application No PCT/AU90/00471. (It will be
appreciated that milling in other types of high energy ball
mill for an appropriate period of time should have the same
effect.) The milling was effected for a period sufficient
- to convert the particulate ilmenite charge of the ball mill
into a nanostructural material. This required high energy
ball milling for a period of time which depended upon the
milling conditions and the additive(s) to the ball mill
charge.
The milled samples were then le~heA with no further
treatment.
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2169~9~7 ;-
-- 7
At different stages of the experiments, the composition of
each sample was assessed using one or more of the following
techniques: x-ray diffraction; Mossbauer spectroscopy;
transmission and scanning electron microscopy; atomic
absorption spectrometry; Rutherford backscattering
spectrometry. In particular, structural development of the
as-milled samples was monitored by x-ray diffraction of
cobalt Ka radiation using a Phillips diffractometer, and
Rutherford backscattering spectrometry was used to analyse
the presence of iron in chemically leached samples.
A range of additives were used with the initial charge of
the ball mill. In each experiment, the additive remained
in the charge of the ball mill for the duration of the
milling. Although there was some variation of the
concentration of some of the additives, no attempt was made
to optimise their concentrations or their reducing
properties. One control experiment was carried out using
ilmenite alone (that is, with no additive to the charge of
the ball mill).
Particular additives used in the experiments were as
follows:
1. DDAA (didodecyl dimethyl ammonium acetate);
2. DDAB (didodecyl dimethyl ammonium bromide);
3. DHDAA (dihexadecyl dimethyl ammonium acetate);
4. DDAOH (didodecyl dimethyl ammonium hydroxide);
5. SDDS (sodium didodecyl sulphate);
6. Do~e~An~-; and
7. Amorphous boron.
WO95/08004 2 1 6 9 9 4 7 PCT/AU94/00550
During the milling - which lasted for up to 300 hours - the
charge of the ball mill was held at room temperature (about
25C). For experiments using the additives 1 to 5 above,
the milling was performed in aqueous solution. Considering
the point of zero charge of the ilmenite particle, it was
necec~Ary to ad;ust the pH of the aqueous solution of the
additives DDAA, DDAB and DHDAA so that it had a value of
10, which corresponds to negatively charged ilmenite
particles, in order to get adsorption of the cationic
species. For the experiments with the additive SDDS, the
pH was adjusted to a value of 5, which corresponds to
positively charged ilmenite particles, in order to get
adsorption of the anionic surfactant SDDS. Potassium
hydroxide and potassium chloride were used for pH
adjustment. No adjustment of the pH of the aqueous
solution was necessary for experiments with the additive
DDAOH.
The nanostructural ilmenite products obtAin~ by milling
the ilmenite with the additives (i) DDAOH, (ii) SDDS and
(iii) amorphous boron, were leached with 4M hydrochloric
acid at temperatures ranging from 80C to 100C. The
Rutherford backscattering spectroscopy spectra of the
leAche~ materials showed
(a) that less than 5 atomic per cent of the iron in the
sample milled with DDAOH remained after leaching; and
(b) there had been a significant reduction of the iron
content of the ilmenite samples that had been milled
with SDDS and with amorphous boron.
WOg5/08004 PCTIAU94/00550
~1~99~7
The x-ray diffraction pattern of the material milled with
DDAOH and then le~c~e~ with hydrochloric acid showed only
peaks corresponA~ng to rutile.
Thus the experiments showed that prolonged milling of
ilmenite with an appropriate additive produces a
nanostructural powder that is amenable to lP~h~ng with hot
hydrochloric acid to remove the iron component of the
ilmenite and leave rutile (TiO2).
