TiO2 containing product including rutile, pseudo-brookite...

Details TiO2 containing product including rutile, pseudo-brookite... TiO2 containing product including rutile, pseudo-brookite...

1997-08-29

2003-03-11

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C423S069000

Reexamination Certificate

active

06531110

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of preparing a high grade titanium dioxide (TiO
2
) product from titania slags by removing alkaline earth and other impurities usually found in slags. The method of the present invention generally comprises the steps consisting of sizing the slag, oxidizing it at high temperature, reducing the resulting material at high temperature, subsequently acid leaching the reduced material at elevated temperature and pressure to yield an upgraded slag product and a leachate, and finally calcining the leached product. The upgraded slag obtained from the inventive method is a suitable feedstock for the chloride process of TiO
2
pigment production.
Optionally, the upgrading process may also comprise a caustic leaching step performed immediately after the acid leaching step. The caustic leaching step will be particularly useful to remove residual SiO
2
in the upgraded product.
2. Description of the Prior Art
Titanium Feedstocks for TiO
2
Pigment Production
The present invention is directed to a process for the upgrading of titania slags into a product having a very high TiO
2
content with low levels of alkaline-earth and other impurities.
Titanium is the ninth most abundant element in the earth's crust. Of the various titanium based products, titanium dioxide (TiO
2
), holds the greatest industrial and commercial significance. It is a high-volume chemical in most of the industrialized world. Titanium dioxide is used as pigment in paints, plastics, papers, inks, etc.
Titanium dioxide (TiO
2
) is commonly found in nature in the form of “ilmenite” ores containing from 30 to 65% TiO
2
in association with varying amounts of oxide impurities of the elements iron, manganese, chromium, vanadium, magnesium, calcium, silicon, aluminum and others. Ilmenite ores are commercially upgraded into titania “slag” containing typically 70-90 wt % TiO
2
by electro-smelting processes conducted at very high temperatures (molten state) in electric arc furnaces. Ilmenite ores are also upgraded into “synthetic rutile” products containing 92-95 wt % TiO
2
by processes consisting in the “leaching” of ilmenite ores with mineral acids or in reducing the iron oxide impurities in the presence of coal at moderately high temperatures (solid state reduction) in rotary kiln type furnaces. “Rutile” is a still richer form of TiO
2
(93-96% TiO
2
) which occurs naturally but is rarely found in deposits of commercial significance.
The production of TiO
2
pigments is based on two processes. The traditional “sulfate” process consists in solubilizing ilmenite or slag by dissolving it in concentrated sulphuric acid; pure TiO
2
is then obtained by selective hydrolysis of the liquors containing the solubilized TiO
2
. In the newer “chloride” process, a feedstock such as ilmenite, slag, synthetic rutile or natural rutile is fluidized at high temperature (typically 950-1200° C.) in a stream of chlorine gas to produce a vapour mix of chlorides, including TiCl
4
and the chlorides of the feedstock impurities; TiCl
4
is separated from the impurity chlorides by selective condensation and is subsequently converted to pure TiO
2
by contacting it with oxygen at high temperatures (chlorine gas is recovered in the oxidation treatment).
The main technical requirement for sulfate process feedstocks is that these must be soluble in concentrated sulphuric acid. For the chloride process, however, the main technical requirements are: i) the feedstock must contain low concentrations of alkaline-earth oxides such as MgO and CaO, and ii) the particle size range must be compatible with the fluid bed equipment used to chlorinate the feedstock. In addition, environmental and economic considerations dictate the need for the highest possible TiO
2
contents in the feedstock.
The present invention relates specifically to the preparation of a high grade TiO
2
feedstock suitable for the fast growing chloride pigment process by upgrading titania slags. The initial slag can be naturally low in alkaline-earth oxide impurities, such as the slag produced from ilmenite ores mined in the East Coast of the Republic of South Africa, or could contain higher levels of these impurities, as is the case of slag produced from ilmenite ores mined in the Province of Quebec, Canada. In both cases the resulting upgraded product is of similar TiO
2
contents (typically 94-96% TiO
2
) and exhibit contents of alkaline-earth oxides well below the maxima generally acceptable for chloride feedstocks (1.5% MgO and 0.20% CaO) This is an important aspect of the invention since the use of slags containing higher levels of alkaline-earth oxides has been up to now restricted to the sulfate pigment process.
Oxides of the alkaline earth metals such as MgO and CaO are undesirable in the chloride pigment process as they form during chlorination paste-like condensates of MgCl
2
and CaCl
2
which tend to foul the fluidizing reactors and other downstream equipment. However, alkaline-earth oxides are commonly found in magmatic TiO
2
-bearing deposits known as rock ilmenites which represent the most abundant sources of TiO
2
. Rock ilmenites, being relatively low in TiO
2
contents (30-45% TiO
2
) but containing high concentration of iron oxides, can only be economically upgraded by electro-smelting processes which produce a titania slag and recover the iron values in the form of high purity iron products, the latter feature not being possible in other commercial ilmenite upgrading processes. While electro-smelting of rock ilmenites renders the resulting slag suitable as a feedstock for the sulfate process, the smelting does not remove sufficient amounts of impurities, such as alkaline-earth impurities, including magnesium and calcium, to make the slag suitable as a feedstock for the chloride process.
There is therefore a need to provide a commercially attractive method for further upgrading slags obtained from ilmenites, including those ilmenites naturally high in alkaline-earth impurities, to yield a suitable high grade feedstock for the chloride process of TiO
2
production.
Unexpectedly, it has been discovered that titania slags can be treated in a novel and commercially efficient process to produce an upgraded slag product which is an excellent feedstock for the chloride process.
Differences Between Slags and Ilmenites
The literature contains a number of prior art processes aimed at the upgrading of ilmenite ores into synthetic rutile type products by applying mineral acid leaching techniques.
These processes are not applicable to the upgrading of titania slag because of the vastly different chemical and physical nature of ilmenite ores and titania slags. As will be shown in the figures which form part of this application, it is manifest that the X-ray diffraction patterns of ilmenite ores and slags are quite different indicating that their chemical and physical properties are also quite different. What follows is a description of the chemical and physical differences separating ilmenite ores from titania slags.
Ilmenite ores are found in nature as primary ilmenites (FeTiO
3
) or weathered ilmenites and mixtures thereof. Weathered ilmenites result from oxidation by ground water which gradually transforms primary ilmenites through the following major phases: pseudorutile (Fe
2.3
Ti
3
O
9
), altered pseudorutile (Fe
1.2
Ti
3
O
6.6
(OH)
2.4
), leucoxene (Fe
0.6
Ti
3
O
4.8
(OH)
4.2
) and finally natural rutile (TiO
2
). The prior art has evolved various processes for upgrading ilmenites (primary, secondary and mixtures thereof) to synthetic rutile by concentrating the TiO
2
content and removing iron as well as various gangue minerals and other impurities by mineral acid leaching processes. These prior art processes, which will be discussed in greater detail below, are usually adapted for use with ilmenites and do not yield satisfactory results with titania slags mainly because slags are physically and chemically different from ilmenites.
Titania slags are generally produced by reduction smelti

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