Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Reexamination Certificate
1998-10-19
2002-02-12
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
C423S082000, C423S086000, C241S023000, C241S024140, C209S038000
Reexamination Certificate
active
06346223
ABSTRACT:
DESCRIPTION OF THE INVENTION
The present invention discloses an innovative process for producing a titanium concentrate having contents of titanium and iron close to those usually found in ilmenite concentrates. Said material, herein called “artificial ilmenite”, is obtained by applying pyro and hydrometallurgical processes to the treatment of highly impure titanium ore, a class into which can be found in Brazilian ores, the predominant titanium source of which is anatase.
The processes for the production of titanium and its compounds are schematically shown in FIG.
1
. Presently, there are only two ore sources commercially exploited around the world: rutile (TiO
2
) and ilmenite (FeTiO
3
). Several alternatives involving physical and/or chemical beneficiation processes for concentrating such ores have been proposed (HENRY, J. L. et all., “Bureau of Mines Development of Titanium Production Technology”, Bulletin 690, U.S. Bureau of Mines, 1987). The products obtained this way have essentially two destinations: direct production of metallic titanium and production of titanium pigment. The latter is presently carried out through the so-called sulphate and chloride processes, wherein the latter process is the main one and that with the highest growing potential.
Among the items shown in
FIG. 1
, the production of titanium slag (85% TiO
2
equivalent) is of utmost importance due to the tact that this material can be directly used in the two presently available routes for the production of TiO
2
pigment, by far the main application of titanium based raw materials. The following advantages can be mentioned for the production of slag: possibility of using titanium ore with a lower impurity content (ilmenite), utilization of the iron content of said ore through the production of pig iron, in addition to the already mentioned advantage of producing a material which can employed in the existing processes for the production of pigment. Estimates for the titanium slag consumption by the pigment industry show a present increase of up to 600,000 metric tons until year 2000 (ANON., “Titanium Minerals 1994—A Complete Cost Analysis”, AME Mineral Economics, 1994).
Brazil possesses approximately 20% of the known titanium ore reserves and the main concentration thereof can be found in alkaline pipes in the western region of Minas Gerais State and south of Goias State. The ore, that covers phosphate beds, is of complex nature, being the result of alterations in different types of rocks. The main difficulty in developing a process for recovering titanium amounts from this type of ore is the selection of single operations that show high efficiency and selectivity simultaneously. As a consequence, when trying to produce a concentrate rich in titanium the overall mass recovery falls dramatically, rendering the process uneconomical. Treatments of such kind have been tried in the past (PAI{overscore (A)}O, J. M. J. and MENDON
A, P. A. F., “Process for Concentrating Titanium Ores”, Brazilian patent PI 7507645; (PAX{overscore (A)}O, J. M. J. and MAGALH{overscore (A)}ES, G., “Process for Beneficiating Titanium Ores”, Brazilian patent PI 7604532), resulting in alternatives of limited practical use, since mass recoveries have been comprised within the 5 to 10% range only.
The process here presented has been developed with the main purpose of overcoming the severe drawbacks found in the processes avaliable to date for the treatment of Brazilian anatase ores. As shown later; the solution for such a problem is obtained through by the utilization of iron amounts usually associated to titanium in the several anatase deposits found in Brazil.
The objective of the present process is the recovery on a titanium concentrate having a chemical composition similar to that of ilmenite; this concentrate being the intermediate raw material for the production of titanium slag. On the other hand, the process for producing slag is based on the carbothermic reduction of a part of the titanium contained in the ore—leading to a material with a stoichiometry close to Ti
3
O
5
—and all the iron from the concentrate to FeO—contained in the slag phase—and metallic Fe. Other elements such as aluminium, silicon, alkaline and alkaline-earth metals are not reduced and thus constitute deleterious impurites that must be removed from the titanium raw material. Phosphorus is also an undesirable impurity due to the contamination caused in the resulting pig iron. As can be seen hereinbelow, the process developed makes it possible to obtain a high degree of removal of such impurities, thus providing concomitantly a large recovery of titanium and iron contained in the raw ore.
The process described in the present invention is based on the use of the following sequence of operations to the processing of titanium ores: disintegration, screening through 6 mm, crushing, classification, low intensity magnetic separation for removing coarse magnetite, attrition and slimes removal for discarding the minus 74 &mgr;m (200 mesh) fraction, calcination in the presence of sodium carbonate (Na
2
CO
3
) and/or potassium carbonate (K
2
CO
3
), comminution of the calcination product to a particle size below 1 mm, leaching in alkaline medium (pH in excess of 10) and later acid leaching. Each of such steps is detailed below.
First of all, the raw ore is subjected to a disintegration step in a drum washer, followed by screening in a vibrating screen having a 6 mm (¼″) opening, and crushing in a conical crusher. The screen operates in closed loop with the crusher, that is, only the >6 mm fraction is crushed. The screened material is classified in a spiral classifier which is adjusted for providing a product with a particle size above 48 mesh (300 &mgr;m). The overflow of the classifier with a particle size of −48 mesh is discarded.
The classified ore is then subjected to a low intensity magnetic separation (approximately 800 Gauss), preferably in a wet drum separator. The magnetic fraction is discarded. The non magnetic fraction undergoes a slimes removal operation in an attrition cell with the purpose of removing clay-minerals particles that remain adhered to the surface of the anatase grains. The ore from the attrition step is classified in a spiral classifier adjusted in such a way that a 200 mesh (74 &mgr;m) cut can be obtained. The overflow of the classifier, with a particle size of—200 mesh, is discarded. For the purposes of the present invention, the material subjected to the above mentioned sequence of operations, that is, disintegration, screening, crushing, classification, magnetic separation, attrition and slimes removal, is called mechanical concentrate.
In the calcination step, the mechanical concentrate is mixed with sodium carbonate (Na
2
CO
3
) and/or potassium carbonate (K
2
CO
3
) and heated to a temperature within the 900 to 1300° C. range, preferably 1100° C., being kept at the desired temperature for a time period between 20 to 60 minutes, preferably 30 minutes, in an oxidizing environment. The amount of carbonate to be added, either as powder or in aqueous solution, depends on the content of Al
2
O
3
and SiO
2
, ranging from 60 to 150 kg per metric ton of ore to be treated. The main purpose of this calcination is to produce soluble sodium compounds (Na
2
O.Al
2
O
3
, Na
2
O.P
2
O
5
, Na
2
O.SiO
2
among others) at elevated temperatures, which are removed in the leaching steps that follow. No agglomeration or sintering was observed in the ore during calcination. Therefore, a simple disintegration of the calcined product is required in order to match its grain size with the next leaching step. In laboratory scale, this is carried out by compressing the calcined product in a rubber mantle, whereas in industrial scale it can be carried out through the use of conventional comminution equipment (hammer or jaw crusher) and care should be taken when regulating the operation of said equipment in order to avoid the generation of excessive fines. The calcined disintegrated product with a particle size below 1 mm feeds the leachin
De Freitas Lino Rodrigues
De Matos Marcelo
Horta Ronaldo De Moreira
Bos Steven
Companhia Vale Do Rio Doce
Rosenman & Colin LLP
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