Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Reexamination Certificate
2001-06-28
2003-09-30
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
C423S084000, C423S118100, C423S132000
Reexamination Certificate
active
06627165
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the removal of impurities from a titaniferous material.
The term “titaniferous material” is understood herein to mean a material which contains at least 2 wt % titanium.
In a particular embodiment the present invention provides a process whereby silica and alumina are removed from a titaniferous material using an aqueous leach in the presence of acid, with the effectiveness of the leach in removing these impurities enhanced by the combination of pretreatments and the conditions of the leach.
In industrial chlorination processes titanium dioxide bearing feedstocks are fed with coke to chlorinators of various designs (fluidised bed, shaft, molten salt), operated to a maximum temperature in the range 700-1200° C. The most common type of industrial chlorinator is of the fluidised bed design. Gaseous chlorine is passed through the titania and carbon bearing charge, converting titanium dioxide to titanium tetrachloride gas, which is then removed in the exit gas stream and condensed to liquid titanium tetrachloride for further purification and processing.
The chlorination process as conducted in industrial chlorinators is well suited to the conversion of pure titanium dioxide feedstocks to titanium tetrachloride. However, most other inputs (i.e. impurities in feedstocks) cause difficulties which greatly complicate either the chlorination process itself or the subsequent stages of condensation and purification. The attached table provides an indication of the types of problems encountered. In addition, each unit of inputs which does not enter products contributes substantially to the generation of wastes for treatment and disposal. Some inputs (e.g. heavy metals, radioactives) result in waste classifications which may require specialist disposal in monitored repositories.
Preferred inputs to chlorination are therefore high grade materials, with the mineral rutile (at 95-96% TiO
2
) the most suitable of present feeds. Shortages of rutile have led to the development of other feedstocks formed by upgrading naturally occurring ilmenite (at 40-60° TiO
2
), such as titaniferous slag (approximately 86% TiO
2
) and synthetic rutile (variously 92-95% TiO
2
). These upgrading processes have had iron removal as a primary focus, but have extended to removal of manganese and alkali earth impurities, as well as some aluminium.
Elemental
Input
Chlorination
Condensation
Purification
Fe, Mn
Consumes
Solid/liquid
chlorine,
chlorides
coke,
foul
increases
ductwork,
gas volumes
make sludges
Alkali &
Defluidise
alkali earth
fluid beds due
metals
to liquid
chlorides,
consume
chlorine, coke
Al
Consumes
Causes
Causes
chlorine,
corrosion
corrosion,
coke
makes
sludges
Si
Accumulates
Can encourage
May require
in
duct
distillation
chlorinator,
blockage.
from product
reducing
Condenses in
campaign
part with
life.
titanium
Consumes
tetrachloride
coke,
chlorine
V
Must be
removed by
chemical
treatment and
distillation
Th, Ra
Accumulates
in
chlorinator
brickwork,
radioactive;
causes
disposal
difficulties
In the prior art synthetic rutile has been formed from titaniferous minerals, e.g. ilmenite, via various techniques. According to the most commonly applied technique, as variously operated in Western Australia, the titaniferous mineral is reduced with coal or char in a rotary kiln, at temperatures in excess of 1100° C. In this process the iron content of the mineral is substantially metallised. Sulphur additions are also made to convert manganese impurities partially to sulphides. Following reduction the metallised product is cooled, separated from associated char, and then subjected to aqueous aeration for removal of virtually all contained metallic iron as a separable fine iron oxide. The titaniferous product of separation is treated with 2-5% aqueous sulphuric acid for dissolution of manganese and some residual iron. There is no substantial chemical removal of alkali or alkaline earths, aluminium, silicon, vanadium or radionuclides in this process as disclosed or operated. Further, iron and manganese removal is incomplete.
Recent disclosures have provided a process which operates reduction at lower temperatures and provides for hydrochloric acid leaching after the aqueous aeration and iron oxide separation steps. According to disclosures the process is effective in removing iron, manganese, alkali and alkaline earth impurities, a substantial proportion of aluminium inputs and some vanadium as well as thorium. The process may be operated as a retrofit on existing kiln based installations. However, the process is ineffective in full vanadium removal and has little chemical impact on silicon.
In another prior art invention relatively high degrees of removal of magnesium, manganese, iron and aluminium have been achieved. In one such process ilmenite is first thermally reduced to substantially complete reduction of its ferric oxide content (i.e. without substantial metallisation), normally in a rotary kiln. The cooled, reduced product is then leached under 35 psi pressure at 140-150° C. with excess 20% hydrochloric acid for removal of iron, magnesium, aluminium and manganese. The leach liquors are spray roasted for regeneration of hydrogen chloride, which is recirculated to the leaching step.
In other processes the ilmenite undergoes grain refinement by thermal oxidation followed by thermal reduction (either in a fluidised bed or a rotary kiln). The cooled, reduced product is then subjected to atmospheric leaching with excess 20% hydrochloric acid, for removal of the deleterious impurities. Acid regeneration is also performed by spray roasting in this process.
In all of the above mentioned hydrochloric acid leaching based processes impurity removal is similar. Vanadium, aluminium and silicon removal is not fully effective.
In yet another process ilmenite is thermally reduced (without metallisation) with carbon in a rotary kiln, followed by cooling in a nonoxidising atmosphere. The cooled, reduced product is leached under 20-30 psi gauge pressure at 130° C. with 10-60% (typically 18-25%) sulphuric acid, in the presence of a seed material which assists hydrolysis of dissolved titania, and consequently assists leaching of impurities. Hydrochloric acid usage in place of sulphuric acid has been claimed for this process. Under such circumstances similar impurity removal to that achieved with other hydrochloric acid based systems is to be expected. Where sulphuric acid is used radioactivity removal will not be complete.
A commonly adopted method for upgrading of ilmenite to higher grade products is to smelt ilmenite with coke addition in an electric furnace, producing a molten titaniferous slag (for casting and crushing) and a pig iron product. Of the problem impurities only iron is removed in this manner, and then only incompletely as a result of compositional limitations of the process.
A wide range of potential feedstocks is available for upgrading to high titania content materials suited to chlorination. Examples of primary titania sources which cannot be satisfactorily upgraded by prior art processes for the purposes of production of a material suited to chlorination include hard rock (non detrital) ilmenites, siliceous leucoxenes, many primary (unweathered) ilmenites and large anatase resources. Many such secondary sources (e.g. titania bearing slags) also exist.
Clearly there is a considerable incentive to discover methods for upgrading of titaniferous materials which can economically produce high grade products almost irrespectively of the nature of the impurities in the feed.
At present producers of titania pigment by the choride process require feedstocks to have silica levels as low as possible. In general most feedstocks are less than 2% SiO
2
. Where, for various reasons, feedstocks with high levels of silica may be taken in, they are blended against other low silica feedstocks, often with significant cost and productivity penalties. Therefore suppliers of titaniferous feedstocks for chlorination traditionally select ores and concentrates which will res
Hollitt Michael John
McClelland Ross Alexander
Bos Steven
Dennison, Schultz & Dougherty
Technological Resources PTY LTD
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