WO2007062434A2

WO2007062434A2 - A mineral recovery process

Info

Publication number: WO2007062434A2
Application number: PCT/ZA2006/000129
Authority: WO
Inventors: Jan Hendrik Becker; Regan Mark Carter
Original assignee: Crestwave Technologies (Pty) Ltd
Priority date: 2005-11-22
Filing date: 2006-11-16
Publication date: 2007-05-31
Also published as: WO2007062434A3

Abstract

The invention provides a mineral recovery process (10) which allows the processing of an ore (12) in order to separate iron (14), titanium (16), silica (18) and vanadium (20) from the ore which mineral recovery process includes the steps of : (a) producing a gaseous reductant (24); (b) treating the ore by way of direct reduction (22) with the gaseous reductant to produce a first product (36); and (c) separating the iron from the first product by way of a pyro-metallurgical process followed by the separation of the titanium, silica and vanadium from the first product by way of a hydro-metallurgical process.

Description

A MINERAL RECOVERY PROCESS

BACKGROUND OF THE INVENTION

[0001] The invention relates to a mineral recovery process and more specificaliy to a mineral recovery process for use with ore bodies that contain large quantities of iron as an impurity element.

[0002] It is normally difficult and expensive to separate large quantities of iron or silicon impurity elements from valuable elements. Current recovery processes of valuable elements from ore bodies which contain large quantities of iron or silicon as impurity elements, such as the titaniferous iron ore body which is common in the Bushveld Igneous Complex in South Africa, provide that the ore is processed in a rotary kiln together with large quantities of coke or anthracite and limestone to produce sponge iron. In order to meet the stringent metallurgical requirements as a reductant it is important that the coal which is used in these processes to produce the coke or the anthracite has a low sulphur content.

[0003] Worldwide coal reserves with low sulphur content are scarce and the production of coking coal is expensive. During the production of coking coal waste or by-products that are not environmentally friendly are also produced. In recent times the price of coking coal has increased to the order of US$200 per tonne.

[0004] The production of sponge iron in a rotary kiln only occupies 15% of the volume of the kiln. The reagents such as coking coal and limestone represent 30% of the charge and 70% of the charge is made up of the iron oxide ore to be treated. Generally INT1210/DD

2 less than 11% of the kiln volume is effectively used for the iron oxide ore. In cases where the iron ore is of a low grade the percentage of ore in the rotary kiln drops even further. This means that a kiln is by and large a slow and costly recovery process.

[0005] A blast furnace is not suitable to treat this kind of ore either because of the presence of rutile or ilmenite in the ore. In view of the fact that the rotary kiln is currently the only suitable process available for this type of ore any improvements in this regard can make the rotary kiln process more efficient and cost effective.

[0006] In certain ore bodies the valuable elements account for less than 2% of the raw ore and in order to recover these valuable elements the entire ore body has to be processed. That means that about 98% of the processed material will be lost and is dumped as waste. This adds to production time, expenses and environmental impact.

SUMMARY OF THE INVENTION

[0007] The invention aims to provide an alternative mineral beneficiation or second process which might solve some of the aforementioned problems.

[0008] The invention provides a mineral recovery process which includes the steps of :

(a) producing a gaseous reductant;

(b) treating ore by way of direct reduction with the gaseous reductant in a rotary kiln to produce a first product; and

(c) separating minerals in the first product from one another. INT1210/DD

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[0009] The gaseous reductant may be produced from any hydrocarbon feedstock. The hydrocarbon feedstock may be in the form of waste material such as low-grade coal. The gaseous reductant is preferably produced in a gasifier and the process may include the step of feeding steam into the gasifier.

[0010] The process may include the step of scrubbing the gaseous reductant to remove any impurities that might be detrimental to the direct reduction process.

[0011] The process may include the step of magnetically separating iron from the first product. The process may include the step of briquetting the separated iron.

[0012] The process may include the step of treating the first product by way of a salt roasting to produce a second product.

[0013] The process may include the step of dissolution and filtering of the second product. During the filtration a titanium concentrate may be separated from the second product.

[0014] The process may include the step of precipitating some of the material in the filtrate, obtained from the second product, from the dissolution step. Silica may be separated from the second product during the precipitation step.

[0015] The process may include the step of a second precipitation from the filtrate obtained from the second product, to produce a third product. The third product may be in the form of vanadium.

BRIEF DESCRIPTION OF THE DRAWING INT1210/DD

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[0016] The invention is further described by way of an example with reference to the accompanying flow sheet, Figure 1 , which is a schematic representation of a mineral recovery process according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0017] Figure 1 illustrates a mineral recovery process 10 which allows the processing of an ore 12 in order to separate iron 14, titanium 16, silica 18 and vanadium 20 from the ore 12.

[0018] The ore 12 is treated by way of direct reduction in step 22. The direct reduction takes place in a rotary kiln and is achieved by treating the ore 12 with a gaseous reductant 24. The reductant 24 is directly introduced into the kiln and can also be used as burning fuel for the kiln.

[0019] The kiln is internally heated by making use of the same gas produced in the gasifier but in this instance as a fuel.

[0020] The reductant 24 is in the form of a mixture of carbon monoxide and hydrogen. The exact mixture of carbon monoxide and hydrogen can vary and in this example is in the order of 30% to 70% carbon monoxide and 30% to 70% hydrogen with a target mixture of 50% carbon monoxide and 50% hydrogen.

[0021] The reductant 24 is produced in a gasifier in a step 26 from a suitable hydrocarbon feedstock 28 and by introducing steam 30 into the gasifier.

[0022] The feedstock 28 can be in the form of any appropriate hydrocarbon source such as waste material, for example low-grade'coal material. Excess sulphur in the INT1210/DD

5 reductant 24 as well as very fine solid material produced in the gasifier is removed by way of a scrubber in a step 32. This results in a high quality clean gaseous reductant 24.

[0023] After completion of the direct reduction in the kiln in step 22 the product is milled to a suitable particle size in step 34 to deliver a first product 36. The first product 36 is in the form of a powder and the iron 14 contained therein is then separated from the other mineral contained in the first product 36.

[0024] Exhaust gasses 38 which exit the kiln are recycled to the gasifier for reuse.

[0025] The first product 36 is subjected to magnetic separation in a step 40, which separates the iron 14 as powder from the first product 36. The iron powder 14 is compacted into briquettes 42 in a step 44.

[0026] The tailings or remainder of the first product 36, after the magnetic separation step 40, is subjected to a roasting step 46 which can for example be in the form of a salt roasting. The roasting 46 takes place in a rotary kiln in a known manner and produces a second roasted product 48.

[0027] Depending on the type of ore 12 the second product 48 is for example dissolved in water and then subjected to a filtration in step 50. This is to separate the undissolved slurry that contains the titanium concentrate 16 from the second product 48.

[0028] Again, depending on the type of ore 12, the remainder of the second product 48 is after filtration subjected to a precipitation in step 52. This results in the separation of the silica 18 from the second product 48. INT1210/DD

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[0029] The remainder of the second product 48, after the filtration step 50 and the precipitation step 52, is treated with ammonia to form ammonium meta-vanadate 54.

[0030] The ammonium meta-vanadate 54 is firstly filtered from the aqueous solution. This is followed by a roasting step 56 in a suitable furnace to produce a third roasted product 58 which is vanadium 20 in the form of V₂O₅.

[0031] The method of separating the various minerals from the first product 36 might vary depending on the type of ore 12. The process 10 described in this example relates to an ore 12 that contains iron, titanium, silica and vanadium in varying concentration and forms. The process can also be used in the recovery of various other complex minerals such as a copper-cobalt iron containing ore.

[0032] In essence the iron 14 is removed by way of a pyro-metallurgical process through the direct reduction, milling and magnetic separation of the ore 12 in the steps 22, 34 and 40 followed by a hydro-metallurgical process for the separation of the remaining valuable elements such as the titanium 16, silica 18 and vanadium 20.

[0033] The process 10 can for example be used in respect of an ore 12 with the following chemical composition:

• 12 to 14% TiO₂;

• 1.5 to 1.7% V₂O₅;

• 70 to 75% Fe₃O₄; and • Silicates.

[0034] Examples of this ore 12 are found in the Bushveld Igneous Complex in South Africa and also in various other parts of the world. INT1210/DD

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[0035] Although the ore 12 is a magnetite ore the iron content is in this case only in the order of 52 to 55%, which is low, compared to the high-grade magnetite and hematite ores available with an iron content of 65% and higher. The presence of the rutile makes the ore 12 unsuitable for conventional steel making processes such as in a blast furnace.

[0036] The ore 12 is subjected to the direct reduction and milling in the steps 22 and 34 which allows the removal of the iron 14 by way of the magnetic separation step 40. The iron 14 is in the form of sponge iron, clean and void from excessive carbon, limestone and other detrimental by-products as a result of the direct reduction of the ore 12 by way of the gaseous reductant 24.

[0037] The remainder of the first product 36, after the magnetic separation step 40, has a high concentration of vanadium and titanium. The concentrations of vanadium and titanium are for example increased to between 5 to 6% for V₂O₅ and 40 to 45% for TiO₂ as these are now concentrated in 25% of the original ore 12. The other element in the tails from the first product 36 is a silicate 18.

[0038] The vanadium 20 is separated from the titanium 16 by way of the known salt roast process and the silicates 18 are removed by precipitation of the water, glass as silica.

[0039] The process 10 allows the recovery of the iron fraction 14, titanium fraction 16, silica fraction 18 and vanadium fraction 20 from the ore 12 as resalable, separate elements. INT1210/DD

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[0040] The efficiency of the separation process of the titanium 16, silica 18 and vanadium 20 is enhanced by the prior removal of the iron 14 as these elements are now present in higher concentrations in the tails as a result of the removal of the iron 14.

[0041] No structural changes have to be made to the rotary kiln that will be used for the direct reduction operation. As the reductant 24 is void of sulphur no need is required for the use of limestone. No solid reductant is required in view of the fact that a gaseous reductant is used. This means that the capacity of the kiln for the direct reduction step 22 is increased in the order of 30% simply because the limestone and solid reductant is totally excluded.

[0042] An inexpensive feedstock 28 can be used to produce the reductant 24 via the gasifier instead of the very expensive coking coal. The current cost of low-grade coal is currently less than US$15 per tonne. As the exhaust gas 38 is returned to the gasifier step 26 for reuse the risk of releasing harmful gasses into atmosphere is reduced.

[0043] Reduction of the ore 12 by way of a gaseous reductant 24 occurs much faster than is the case with a solid reductant. This results in a further production increase as a result of the reduced retention time in the kiln used in the direct reduction step 22.

[0044] Additionally a lower production temperature is possible as the reductant 24 is made up of carbon monoxide and hydrogen, which should give the same result at temperatures below 1000⁰C compared to conventional direct reduction processes at higher temperatures. INT1210/DD

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[0045] In view of the fact that the same gas that is used as the reductant 24 heats the kiln internally, no expensive fuels such as diesel or paraffin is required as heating media. It also replaces low-grade sulphur bearing pulverized coal to fire the kiln.

Claims

INT1210/DD10 CLAIMS

1. A mineral recovery process which includes the steps of:

(a) producing a gaseous reductant;

(c) separating minerals in the first product from one another.

2. A mineral recovery process according to claim 1 wherein the gaseous reductant is produced from a hydrocarbon feedstock.

3. A mineral recovery process according to claim 2 wherein the hydrocarbon feedstock is in the form of low-grade coal.

4. A mineral recovery process according to claim 1 , 2 or 3 wherein the gaseous reductant is produced in a gasifier.

5. A mineral recovery process according to claim 4 which includes the step of feeding steam into the gasifier.

6. A mineral recovery process according to any one of claims 1 to 5 which includes the step of scrubbing the gaseous reductant to remove impurities.

7. A mineral recovery process according to any one of claims 1 to 6 which includes the step of magnetically separating iron from the first product.

8. A mineral recovery process according to claim 7 which includes the step of briquetting the separated iron. 1NT1210/DD

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9. A mineral recovery process according to any one of claims 1 to 8 which includes the step of treating the first product by way of a salt roasting to produce a second product.

10. A mineral recovery process according to claim 9 which includes the step of dissolution and filtering of the second product.

11. A mineral recovery process according to claim 10 wherein during the filtration, a titanium concentrate is separated from the second product.

12. A mineral recovery process according to claim 10 or 11 which includes the step of precipitating some of the material in the filtrate, obtained from the second product, from the dissolution step.

13. A mineral recovery process according to claim 12 wherein silica is separated from the second product during the precipitation step.

14. A mineral recovery process according to any one of claims 10 to 13 which includes the step of a second precipitation from the filtrate, obtained from the second product, to produce a third product.

15. A mineral recovery process according to claim 14 wherein the third product is in the form of vanadium.