BRIQUETTE

Abstract

The invention relates to the use of fibres, often in briquettes, and to the production of briquettes, for instance from coal, metal or metal ores. Typically the briquettes are formed from particulate material and a fibre.

Claims

1. A briquette comprising: (i) a particulate material; and (ii) in the range 0.1 - 0.5 wt% fibre.

2. The briquette of claim 1, wherein the fibre is a cellulose-containing fibre.

3. The briquette of claim 1, wherein the fibre is a textile or paper derived fibre.

4. The briquette of claim 1, wherein the bulk density of the fibre is in the range 20 - 500 g/l.

5. The briquette of claim 1, wherein at least 90% of the fibre has a length of from about 0.2 mm to about 5 mm.

6. The briquette of claim 1, further comprising a binder selected from at least partially saponified polyvinyl alcohol, a combination of polyvinyl alcohol and sodium hydroxide, an alkali metal alkyl siliconate or polyalkyl silicic acid, phenol formaldehyde resin, guar gum, a combination of guar gum and calcium oxide, anionic polyacrylamide, styrene acrylate emulsion, a polysaccharide binder, and combinations thereof.

7. The briquette of claim 1, comprising 0.01 to 1.5 wt% binder.

8. The briquette of claim 1, wherein the particulate material is selected from a metal ore, metal ore containing waste, iron residue, iron filings, mineral waste, a carbonaceous material, arc furnace waste, MDF sawdust or combinations thereof.

9. The briquette of claim 8, wherein the metal ore comprises iron ore.

10. The briquette of claim 8, wherein the carbonaceous material comprises coke or coal.

11. The briquette of claim 1, wherein the particulate material has a particle diameter of 4 mm or less.

12. The briquette of claim 1, wherein at least 10 wt% of the particulate material is capable of passing through a 100 .Math.m sieve prior to forming into a briquette.

13. The briquette of claim 1, additionally comprising in the range 0.01 to 5 wt% of a cross-linking agent.

14. The briquette of claim 13, wherein the cross-linking agent comprises glutaraldehyde.

15. The briquette of claim 1, additionally comprising a waterproofing agent, combined with the particulate material or as a layer on the external surface of the briquette.

16. Thebriquette of claim 15, wherein the waterproofing agent comprises a styrene-acrylate copolymer or a bitumen emulsion.

17. Thebriquette of claim 1, further comprising a carbon additive.

18. Thebriquette of claim 1, having a moisture content of <15 wt%.

19. Thebriquette of claim 1, further comprising a hardener.

20. A method for producing a briquette of claim 1 comprising: (i) mixing the particulate material, with in the range 0.1 - 0.5 wt% fibre; (ii) compressing the mixture to form a briquette; and (iii) curing the briquette.

21. Themethod of claim 20, further comprising the step of mixing one or more of a binder, a cross-linking material, or a waterproofing agent with the particulate material.

Description

[0053] In order that the invention may be more readily understood, it will be described further with reference to the specific examples hereinafter.

EXAMPLE 1: MAGNETITE

[0054] A magnetite sample consisting of 65 wt% Fe.sub.3O.sub.4 and 2 -30 wt% FeO (particle size of <90 .Math.m) was provided. This was formed into Briquettes using a HUTT-Greaves roller press (pressure of 200 Bar). The Fibres used were CFF Topcel fibres (cellulose fibres). The moisture content and fibre level was varied as shown in Table 1 below.

TABLE-US-00001 Description Ref Green Crush Strength (N) Cured Crush Strength (N).sup.# RI (r180) ISO Test.sup.∗ Control (no fibres) -dry 135/98B Not measured 3980 58.4% No fibres - 8 wt% moisture content 421/20B <40 Low yield 2450 51.6% 0.2% fibres - 8 wt% moisture content 300/19B 68 3680 68.1% # ISO 4700 - mean value from 50 tests .sup.∗ ISO 7215 - results desirably in the range 60 - 80%

[0055] As can be seen, in the absence of fibres, a dry sample provides a cured strength of just under 4000N, which is sufficient to allow transport and storage without damage or disintegration, and processing through a blast furnace. However, the RI (reduction index), a measure of the rate of reduction by function of oxygen loss, fell below the 60% threshold level for reduction rates. Not meeting this standard has a negative effect on the marketability of the product.

[0056] When the moisture content is increased to 8 wt%, mimicking the effects of, for instance, storage of the mineral in a damp environment, it was difficult to process the briquette in the absence of fibres. The briquettes formed had poor integrity and the levels of wastage were high (resulting in low yields). This is shown by the low cured crush strength and low RI results.

[0057] However, when 0.2 wt% fibres was added to the mineral in the presence of the same level of moisture (8 wt%) very good briquettes were formed. These had a good green crush strength, allowing for processing without fear of disintegration, a cured crush strength comparable to the dry mineral and an excellent RI value. Thus, this test shows the benefit of the presence of the fibres in terms of: [0058] Stabilised rheology of the mix to give good compaction parameters [0059] Reinforcement of the structure to increase strength [0060] Enable processing of materials at raised moisture contents

[0061] Further, a study of the briquette structure showed an increase in the voidage/porosity of the briquette, increasing the total surface area across which reduction (e.g. during processing to extract metal) can occur. This results in improved processing times of the briquettes.

EXAMPLE 2: IRON ORE PELLET FINES

[0062] Briquettes were formed from hematite Iron Ore fines (>65% Fe) containing 0.25 wt% cellulose fibres and an organic binder. Less degradation was observed during the hematite to magnetite reduction process (Fe.sub.2O.sub.3 .fwdarw.Fe.sub.3O.sub.4 at 500 - 760° C.), than in the absence of fibres. As noted above, this is believed to be because the fibres allow space for the crystal growth which occurs during this conversion but which will otherwise cause micro cracks in the briquette reducing the briquette strength and leading to disintegration.

[0063] The test results provided in Table 2 below illustrate this principle.

TABLE-US-00002 Sample RDI Test Results Without fibre 53.2 - 3.15 mm With fibre 18.3, 12.0 - 3.15 mm .sup.∗ Reduction Disintegration Index ISO 4696-2

[0064] It can be clearly seen that in the fibre improves the RDI value of the briquette significantly (by 38%). It is generally desirable for RDI values for iron ore briquettes to be as low as possible (ideally less than 10).

EXAMPLE 3: HIGH GRADE ANTHRACITE

[0065] It is typically the case that prior to briquette formation from high grade anthracite, the anthracite has to be washed in order to provide clean sized products. This results in a wet product (superfine tailings in water) which must be dewatered using a press. However, even after dewatering significant moisture remains (for instance in the range 20 - 50 wt%) which makes handling difficult even with extrusion processes.

[0066] It has been found that the addition of 0.2 - 0.4 wt% cellulose fibres (CFF Topcel) to the washed anthracite tailings facilitates the extrusion of the anthracite by controlling moisture content. The level of fibre added depends on the moisture content, with higher levels being required to process high moisture content samples. Further, resistance to flow is increased due to the higher shear force required to process the anthracite-fibre mixture.

EXAMPLE 4: FERRO-NICKEL

[0067] Ferro-nickel of particle size in the range 0.1 - 8 mm was combined with 30 wt% polyvinyl alcohol and 0.3 wt% polyacrylonitrile fibres. The high density of the ferro-nickel restricts the amount of liquid binder that can be added, such that it is often difficult to form a satisfactory film for binding. Further, the mixture becomes saturated so cannot be compacted. The presence of the fibres enabled the briquetting process at moisture levels where typically the ferro-nickel would not bind.

[0068] It would be appreciated that the methods of the invention are capable of being implemented in a variety of ways, only a few of which have been illustrated and described above.

EXAMPLE 5: IRON PARTICULATES

[0069] Briquettes were produced from a blend of secondary product streams with a high residual iron content. A Komarek DH450 roller press was used to form the briquettes at a pressure of 210 bar

[0070] To enable a satisfactory green and final strength, fibres were added to the proprietary binder formulation at a dose of 0.0 to 0.5%. The 0 percent fibre test is included as a comparative example.

[0071] Yield was calculated as % by weight of formed briquettes on first pass of the material through the press.

[0072] Strength was measured by testing individual briquettes to peak load on a Mecmesin Omni-test compressive strength tester, with a load rate of 10 mm/min. The average result was recorded from 6 briquettes per variable. Green strength was tested at <1 hour from production, and Cured strength at 48 hours after production.

TABLE-US-00003 Results and Observations: Percentage Addition of fibers Yield (% of acceptably formed briquettes) Average Green strength Average Cured strength 0 <5% Not measurable 1077N 0.1 78% 78N 2624N 0.2 89% 101N 4442N 0.3 90% 96N 4312N 0.4 83% 95N 4505N