TECHNICAL FIELD

[0001] The present invention relates to a method for producing a chromite agglomerate from a particulate chromite. More particularly, the method of the present invention relates to a method for producing a chromite agglomerate by mixing a particulate chromite with a silicon chain-based reagent.

BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an

acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Chromite is conventionally agglomerated prior to smelting. Existing techniques for producing chromite agglomerates employ pelletising and sintering with coke or coal, a highly energy-intensive process which is necessary to strengthen the chromite pellets sufficiently to withstand the materials handling and high temperatures associated with smelting.

[0004] An advantage of particular embodiments of the present invention is that they may be operated at temperatures below those associated with sintering, including ambient temperatures, to produce a chromite agglomerate having the requisite strength to withstand the materials handling and high temperatures associated with smelting.

SUMMARY OF INVENTION

[0005] A method for producing a chromite agglomerate from a particulate chromite, the method comprising the steps of: controlling the moisture content of the particulate chromite within the range 10 % to 40 % by weight;

combining the particulate chromite with a silicon chain-based reagent; and introducing the particulate chromite into an agglomeration apparatus to produce a chromite agglomerate, wherein the silicon chain-based reagent comprises a compound of formula (I): R ^a [R ^b R ^c SiX] _n R ^d (I) where:

R ^a , R ^b , R ^c and R ^d are, independently, H, OH, d _-4 alkyl, Ci _-4 heteroalkyl including C1-4 haloalkyl, Ci- carboxy and Ci- alkoxy; optionally substituted phenyl, or a halogen;

X is one or more of O, N, or SiR ^a R ^b ; and

n is at least 1 .

[0006] In a preferred form of the invention, the step of combining the particulate chromite with a silicon chain-based reagent occurs prior to the step of introducing the particulate chromite into an agglomeration apparatus to produce a chromite

agglomerate, such that the method comprises the steps of: combining the particulate chromite with a silicon chain-based reagent to produce a silicon chain-based reagent-particulate chromite mixture; then introducing the silicon chain-based reagent-particulate chromite mixture into an agglomeration apparatus to produce a chromite agglomerate.

[0007] In one form of the invention, after the step of introducing the particulate chromite into an agglomeration apparatus to produce a chromite agglomerate, the method comprises the step of: curing the chromite agglomerate for a curing period.

[0008] In one form of the present, the step of curing the chromite agglomerate for a curing period comprises stockpiling the chromite agglomerate for the curing period. As would be understood by a person skilled in the art, the stockpiling may occur during transportation. Preferably, the step of curing the chromite agglomerate for a curing period can be enhanced by providing an increased airflow over chromite agglomerate More preferably, the step of curing the chromite agglomerate for a curing period can additionally or alternatively be enhanced by stockpiling the chromite agglomerate in a low moisture content environment at a temperature above ambient.

[0009] In one form of the president invention, the step of curing the chromite agglomerate for a curing period further comprises the step of:

Polishing the chromite concentrate for a polishing period. [0010] Preferably, the polishing of the chromite concentrate occurs in a revolving drum.

[001 1] In one form of the present invention, the step of curing the chromite agglomerate for a curing period further comprises the step of: coating the chromite agglomerate with an absorbent material.

[0012] Preferably, the absorbent material is selected from chromite concentrate, ferrochrome furnace dusts, sawdust, limestone or coke/coal dusts.

[0013] In preferred form of the invention, the curing period is between 2 to 20 days. Preferably still, the curing period is 7 to 14 days. The inventor has discovered that the curing period should proceed for as until the moisture loss is no longer measurable. In order to determine this, samples of the chromite agglomerate are weighed at regular interval in order to determine when the agglomerates have ceased losing moisture by evaporation. As would be understood by a person skilled in the art, the length of the curing period is highly dependent upon one or more of the following criteria;

Agglomerate treatment after production (stockpile, transportation etc)

Stockpiling techniques and if "turning over" of the stockpile is carried out

Ambient humidity and wind velocity

If advanced desiccants are added for rapid curing which lower surface tension of water such as alcohols, detergents or other desiccating reagents

Lightly heating the agglomerates to between 40-70 °C

Stored under cover or inside a protective environment

Pellet diameter (larger the diameter the slower curing/desiccation)

Polishing process with adsorbent coatings increasing surface area and preventing agglomerates sticking together or to materials handling equipment

[0014] In forms of the invention, the chromite agglomerate of the invention may be a pellet or a granule. In one form of the present invention the size of the produced agglomerate is between 4 mm and 60 mm. As would be understood by a person skilled in the art, the size requirements of the produced agglomerates are dependent on the specific use of the final product. For example, a preferred size range for a ferrochrome furnace would be from 10-18 mm in diameter. As would be understood by a person skilled in the art, a pellet is an agglomerated spheroid composed of mostly fine particles. As would be understood by a person skilled in the art, a granule is an agglomerated spheroid composed of both fine and coarse particles.

[0015] In one form of the invention, the chromite agglomerate of the invention may be an extruded pellet which forms a tube. Preferably, the ration of the length to diameter of the extruded pellet is between 0.3:1 and 2.0:1 . More preferably, the ratio of the length to diameter of the extruded pellet is between 0.75:1 and 1 .5:1 .

[0016] Throughout this specification, unless the context requires otherwise, the term "particulate chromite" refers to an ore, concentrate, or other particulate composition containing chromite, or mixture of two or more of such, which contains the spinel group oxide mineral chromite (also known as chrome spinel), having the generic formula R ⁺² O.R ⁺³ 0 ₃ , where R ⁺² is one or more of Fe ⁺² and Mg ⁺² , and R ⁺³ is at least Cr ⁺³ optionally with one or more of Α ³ and Fe ⁺³ , in ratios specified in Figure 1 .

[0017] For example, the term particulate chromite includes minerals having chemical formulae ranging between FeCr ₂ 0 ₄ through (Fe, Mg)0.(Cr,AI,Fe) ₂ 0 ₃ extending to MgCr ₂ 0 ₄ due to substitution in the crystal by Mg/Fe and Al and Fe/Cr).

[0018] In one form of the invention, the particulate chromite is a smelter waste powder. As would be understood by a person skilled in the art, smelter waste powder is generally disposed of as a toxic waste containing highly toxic chrome 6 valency oxide. Advantageously, the inventors have discovered that the process of the present invention allows the smelter waste powder to be returned to the smelter for conversion of the chromium and iron content to be recovered commercially.

[0019] Without wishing to be bound by theory, the inventors believe that the silicon chain-based reagent of the method of the invention bonds to compounds on the surface of the particulate chromite by hydrolysis of the silicon-chain-based reagent to form a stable siloxane bond with the chromium, aluminum, magnesium, iron, silica and other elements and compounds contained in the particulate chromite. Additionally, the silicon- chain-based reagents act as a coupling agent, and having the ability to cross-link with other silicon-chain-based reagents and the secondary and tertiary siloxanes and silonols. Again without wishing to be bound by theory, that the inventors believe that the cross-linking can also terminate with silicate, hydroxyl and carbonate compounds. [0020] Chromite occurs in a number of geological deposits around the world and is mined for chromium, as well as base and precious metal content. Chromite ores and concentrates are rarely pure chromite and typically have chromium contents of approximately 40% Cr ₂ 0 ₃ , although ores may range as low as 10% and as high as 60%. Chromite concentrates can vary from the above data depending upon the ore and the concentration process.

[0021] During the mining and concentration process a number of minerals associated with the geological deposition of the chromite ores remain attached to the chromite grains or are carried over into the concentrate diluting the chromite and becoming part of the feed to the furnace. The contaminant minerals can vary significantly depending upon the geological mode of formation but common minerals can include pyroxene, amphibole, micas, quartz, serpentinite, feldspars, many sulphide minerals, talc, many other silicate and alumino-silicate minerals, iron oxides, carbonate and calc minerals, chlorite and other oxide minerals.

[0022] Without wishing to be bound by theory, the inventors have discovered that polymerised silicone can bond and cross link with most of the compounds found in chromite concentrates, ores and furnace dusts including Cr, Fe, Ca, Mg, Al, K, Na, Si and C0 ₃ & OH ions. Accordingly, the process of the present invention is not just specific to the chrome spinel itself but equally applicable to other compounds within such materials.

[0023] In a preferred form of the invention, the particulate chromite contains at least 10% by weight chromium oxide (as Cr ₂ O3), as defined above. In a preferred form of the invention, the particulate chromite contains at least 15% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 20% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 25% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 30% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 35% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 40% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 45% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 50% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 55% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 55% by weight chromium oxide. In a preferred form of the invention, the particulate chromite contains at least 60% by weight chromium oxide.

[0024] In a preferred form of the invention, the particulate chromite contains a chromium oxide concentration as a percentage by weight (as Cr ₂ 03) falling within a range having a lower limit selected from the group: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% and 100%; and an upper limit selected from the group 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, wherein the upper limit is higher than the lower limit.

[0025] In one form of the invention, the particulate chromite contains a chromium oxide concentration as a percentage by weight (as Cr ₂ 03) of between 35 and 65%.

[0026] In forms of the invention, the particulate chromite may be consist of high grade ore crushed, or very fine high grade concentrate produced from metallurgical plants where precious and base metals have been extracted and particulate chromite is produced as a by-product.

[0027] Preferably, the moisture content of the particulate chromite is controlled within the range 10% and 30% by weight. Further and still preferably the moisture content of the particulate chromite is controlled within the range 15% and 25% by weight. As would be understood by a person skilled in the art, moisture content is the percentage of water by weight contained per unit of particulate chromite feedstock. The moisture content is measured according to the standard of the operational jurisdiction and can include well known method in the art including ISO, ASTM measurement standards. The moisture content is important to the practical handling of chromite ores, concentrates and wastes. Without wishing to be bound by theory, the applicant believes that feedstocks with a moisture content below 15% moisture is highly dusty and requires special handling and wetting, whilst feedstocks with a moisture content over 25% handles poorly as the material approaches the characteristics of a slurry.

[0028] The moisture content of the particulate chromite is controlled by techniques known to those skilled in the art, such as adding water, and/or blending dryer particulate chromite feedstocks with wetter particulate chromite feedstocks into large blended stockpiles as is the case with all bulk commodities. The moisture will be tightly controlled in commercial operation by the use of on-line moisture meters which will integrate the moisture content of the feed with the accurate addition of the silicon chain- based reagent addition even at high tonnage applications.

[0029] The present invention encompasses the polymers having formula (I) of very large molecular weights, including cross-linked chains. In one form of the present invention the molecular weight of the polymer is at least 100,000 g/mol-1 . As discussed below, such compounds are conveniently dissolved in a solvent to facilitate application to the particulate chromite.

[0030] In one form of the invention, the silicon chain-based reagent comprises a compound of formula (I) where:

R ^a , R ^b , R ^c and R ^d are, independently, H, or Ci _-2 alkyl;

X is O; and

n is at least 1 .

[0031] Without wishing to be bound by theory, it understood by the applicant that the methyl and ethyl units act as the polymerisation and cross-linking agents. It is theorised that they may join together from the free radicals to form longer polymer chains before cross-linking with a silica atom.

[0032] In one form of the invention, the silicon chain-based reagent is a silicon chain-based oil. As would be understood by a person skilled in the art, a silicone oil is any liquid polymerized siloxane with organic side chains. These polymers are used because of their relatively high thermal stability, low surface tension and good mixing properties. Like all siloxanes used in these applications the polymer backbone consists of alternating silicon and oxygen atoms (...Si-O-Si-O-SL.) with side chains attached to the tetravalent silicon centres, or substituents being methyl, ethyl and phenyl groups. By way of example, compounds such as polydimethylsiloxane would be considered to fall within the scope of a silicon chain-based oil.

[0033] In one form of the invention, the compound of formula (I) is a silane, a silonol, a siloxane or a silazane.

[0034] In one form of the invention, the silicon-chain-based reagent is a

polydimethylsiloxane. [0035] In one form of the invention, the compound of formula (l)is selected from a group comprising one or more of: polydimethyl siloxane, cyclopenta siloxane, dimethlymethylcyclo siloxane, decamethylcyclopenta siloxane, dimethyl,

methylpolyethyleneoxidemethylether siloxane, dimethyl, methylglycolcyloxane, polydimethyl siloxane, dimethly siloxane solvent, cyclotetra siloxane,

octamethylcyclotetra siloxane, decamethylcyclopenta siloxane, trimethylated silica, tetra(trimethyl siloxy)silane, dodecamethylpenta siloxane, dimethyl, methylhyroxypropyl, propoxylated siloxane, vinyltrimethoxy silane, methyltrimethoxysilane, vinyltrichloro silane, allyltriethoxysilane, hexamethyldisilazane, dimethyldichlorosilane,

dimethyldiacetate silane, tetramethyl silane, methylacrylatechrome complex,

methylacrylic acid, silyl acetate, silsesquioxanes, (3-(2-aminoethyl)aminopropyl) methyl, methoxy-terminated and -(srimethoxysilyl)propyl)ethylenediamine.

[0036] In a highly preferred form of the invention, the compound of formula (I) is selected from the group: dimethyldichlorosilane, polydimethylsiloxane,

hexamethyldisiloxane, dimethyldiethylsilane and dimethyldiacetatesilane. This highly preferred aspect of the binding chemistry is driven by the reasonable chemical costs, bulk reagent availability and operational flexibility for adjusting the binding chemistry to suit variable feedstock types and characteristics, especially for chromites from differing veins or reefs, concentrate sources and various furnace dust sources. It is the flexability in the reagent fo the present invention which allows for the process of the present invention to be tailored to suit the specific chemicstry of the feedstock, especially if the host rock varies with cross cutting veins through many geological horizons or there is oxidation/weathering.

[0037] The present invention encompasses methods using silicon chain-based reagents comprising combinations of one or more compounds of formula (I).

[0038] In a preferred form of the invention, the chromite agglomerates are furnace- ready. In a preferred form of the invention, the chromite agglomerates are arc-furnace ready. As would be understood by a person skilled in the art, arc-furnace ready means that there is no other requirement necessary before mixing with reductant and flux and feeding to the furnace feeder hopper system and into the upper levels of the furnace operating at 800-1500 °C, for between 2-6 hours. The term "furnace ready" means that the chromite agglomerates are structurally stable during the decent of the chromite agglomerate down into the slag bath of the furnace, with the granules remaining relatively intact and supporting the burden above the slag bath.

[0039] In a preferred form of the invention, the chromite agglomerate is between 10 mm and 18 mm in diameter.

[0040] In one form of the invention, the chromite agglomerate has a compressive strength of at least 150 kg/P. Preferably, the chromite agglomerate has a compressive strength of at least 175 kg/P . More preferably, the chromite agglomerate has a compressive strength of at least 200 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 225 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 250 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 275 kg/P. More

preferably, the chromite agglomerate has a compressive strength of at least 300 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 400 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 500 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 600 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 700 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 800 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 900 kg/P. More preferably, the chromite agglomerate has a compressive strength of at least 1000 kg/P.

[0041] In a highly preferred form of the present invention, the chromite agglomerate has a compressive strength of between 150 -500 kg/P. More preferably, the chromite agglomerate has a compressive strength of between 150 - 400 kg/P. More preferably, the chromite agglomerate has a compressive strength of between 150 - 300 kg/P. More preferably, the chromite agglomerate has a compressive strength of between 150 - 250 kg/P.

[0042] A method of the invention characterised in that the chromite agglomerate has a moisture content of between 1 % and saturation by weight. Preferably, the chromite agglomerate has a moisture content of 1 -50% by weight. More preferably, the chromite agglomerate has a moisture content of 1 -40% by weight. Preferably, the chromite agglomerate has a moisture content of 1 -30% by weight. Preferably, the chromite agglomerate has a moisture content of 1 -20% by weight. Preferably, the chromite agglomerate has a moisture content of 1 -15% by weight. Preferably, the chromite agglomerate has a moisture content of 1 -10% by weight. In a highly preferred form of the present invention, the chromite agglomerate has a moisture content of 1 -5% by weight. As would be understood by a person skilled in the art, whilst a low moisture content is desirable for furnace operation it will not necessary. Should the chromite agglomerates be subjected to water from rain or stockpiling, the moisture content could be much higher, up to saturation. This will not compromise the agglomerate but would be an operational quality control issue for the furnace operator.

[0043] A method of the present invention characterised in that the chromite agglomerate has internal particulate bonding to reduce fines generation if granules are broken. As would be understood by a person skilled in the art, it is advantageous that that the produced agglomerates have sufficient internal cementing to ensure that fragmentation of the agglomerates occurs under compression. Without wishing to be bound by theory, it is understood by the Applicant that the cross-linking of the silicon chain-based reagent during the agglomeration of the feedstock provides sufficient internal cementing to prevent fines generation if the agglomerates are broken. It is envisaged that the broken agglomerate pieces would be fed to a feed system screening system with the sub-fines being returned to the agglomeration circuit and pieces that are still sufficiently coarse to be fed to the furnace.

[0044] A method of the present invention characterised in that the chromite agglomerate comprises a protective shield on the outer surface of the granule. Without being bound by theory, it understood that whilst curing, capillary action draws binder to the surface of the agglomerate developing the protective shield on the outer surface of the granule. This protective shield is more resilient to wear than an interior of the agglomerate and protects the agglomerate from inter-particle erosion to reduce fines generations and the ability of the shield to remain intact at temperatures up to liquidus point.

[0045] In one form of the present invention, the characteristics of the shield are controlled by altering one or more of, the type of selected reagents, the selected reagent dosage or the agglomerate diameter.

[0046] It is understood by the inventor that by altering the thickness of the shield layer that the abrasion resistance of the agglomerate can be adjusted. The thickness of the shield can be engineered by altering reagent dosage or coating chemistry or by altering the agglomerate diameter. It is understood by the applicant that increasing the dosage of the silicon chain-based reagent will increase the shield thickness. It is further understood by the applicant that increasing the agglomerate diameter will also increase the shield thickness. Shield thickness can vary from less than 1 mm to over 5 mm depending upon the diameter of the agglomerate.

[0047] It is further understood by the inventors that the control of the characteristics of the shield can also effect the porosity of the shield layer Variable porosity allows for the ingress and egress of gases, vapours and liquids without compromising

agglomerate strength. The engineered gas-porous shield allows carbon monoxide (CO) gas into the granule matrix without compromising the granule to reduce the chrome spinel to ferro-chrome liquidus inside the granule while still high in the furnace burden. As would be understood by the person skilled in the art, the furnace burden is the height of the raw material above the reaction zone. This is particularly advantageous important as most of the reducing work can be carried out by the reducing gases being generated in the melting and liquid zones

[0048] It has been further discovered by the inventors that the application of a coating during the final formation or post formation of the agglomerate can provide the pellet with additional adjustable surface performance such as hardness, water resistance, non-stick characteristics, reductant or flux coating to enhance furnace performance and increase furnace throughput. Coatings can vary significantly from less than 1 mm to being a shell coating a solid nucleus of chromite or reductant. It is envisaged by the inventors that the coating may be absorbed throughout the entire whole agglomerate matrix, effectively cementing the entre agglomerate. It is envisaged that this may be ustilised where the feedstock contains certain trace elements that require complete cementation, such as uranium tailings. In one form of the present invention, the coating is a waste fines deposited on the agglomerates during curing. Preferably, the waster fines are one or more of coke, coal or furnace dusts. The applicant has discovered that the use of such coatings are particularly useful as they can protect the agglomerates when transported green.

[0049] One of the aspects of the utilisation of the silicon chain-based reagents of the invention is the reduced surface tension of water that these reagents engender in the silicon chain-based reagent-particulate chromite mixture as well as the formation of methanol, ethanol, propanol or glycols during the hydration and bonding of the silicon chain-based reagent to the particulate chromite which enhances the reduction in surface tension, which causes dehydration of the chromite agglomerates. A useful benefit of the dehydration is the formation of a dense, semi-porous to non-porous skin on the chromite agglomerate. The skin acts as a barrier to moisture, air and bacteria. In the case of flux and reductant chromite agglomerates, this skin is useful to keep reactive vapours, gases and sublimates from being gassed off before the core temperature of the chromite agglomerate has reached optimal during the smelting process, ensuring that there is very high conversion of carbon to carbon monoxide to reduce the chrome spinel while held inside the skin eventuating in very high conversion of the chrome spinel crystals to ferrochrome directly inside the chromite agglomerate.

[0050] In the case of non-fluxed & reductant chromite agglomerates a semi-porous shield allows furnace gases to enter the matrix and reduce the chrome spinel while preserving the shape and size of the agglomerate.

[0051] In a preferred form of the invention, the particulate chromite has a silica content of at least 0.5% by weight. Preferably still, the particulate chromite has a silica content of at least 10% by weight. Further and still preferably, the particulate chromite has a silica content of at least 15% by weight.

[0052] In one form of the invention, prior to the step of introducing the silicon chain- based reagent-particulate chromite mixture into an agglomeration apparatus to produce a chromite agglomerate, the method comprises the step of:

Combining a silica flux added to obtain the desired level of pellet silica, with the particulate chromite and/or the silicon chain-based reagent to produce a silicon chain-based reagent-particulate chromite-silica flux mixture. .

[0053] As would be understood by a person skilled in the art, silica flux is a silica containing mineral. In one form of the invention, the silica flux is quartz sand or silica fume. The desired level of pellet silica is directed by the specifications of the smelter.

[0054] In one form of the invention, introducing the silicon chain-based reagent- particulate chromite mixture into an agglomeration apparatus to produce a chromite agglomerate, the method comprises the steps of:

Combining a reducing agent with the particulate chromite and/or the silicon chain-based reagent to produce a silicon chain-based reagent-particulate chromite-reducing agent mixture; and introducing the silicon chain-based reagent-particulate chromite-reducing agent mixture into an agglomeration apparatus to produce a chromite agglomerate comprising a reducing agent.

[0055] In a preferred form of the invention, the steps of:

Combining a reducing agent with the particulate chromite and/or the silicon chain-based reagent to produce a silicon chain-based reagent-particulate chromite-reducing agent mixture; and introducing the silicon chain-based reagent-particulate chromite-reducing agent mixture into an agglomeration apparatus to produce a chromite agglomerate, are undertaken at a temperature between -10C and 60 °C.

[0056] In a highly preferred form of the invention, the steps of:

Combining a reducing agent with the particulate chromite and/or the silicon chain-based reagent to produce a silicon chain-based reagent-particulate chromite-reducing agent mixture; and introducing the silicon chain-based reagent-particulate chromite-reducing agent mixture into an agglomeration apparatus to produce a chromite agglomerate, are undertaken at a temperature between 5 °C to 45 °C .

[0057] An advantage of embodiments of the invention in which a reducing agent is combined with the particulate chromite and/or the silicon chain-based reagent is that this simplifies materials handling, furnace chemistry management and significantly lowers fuel and electricity consumption. Such methods of the invention can be designed to achieve high levels of reduction of the chrome spinel to ferrochrome prior to entering the molten phase of the furnace, with the potential to increase furnace throughput and lower amounts of electricity required to achieve the reduction of chromite ores.

[0058] Conventional techniques for the production of chromite agglomerates necessitate sintering at temperatures under conditions that will induce combustion of a reducing agent, substantially inhibiting the production of chromite agglomerates including a reducing agent, such as those of the present invention.

[0059] In one form of the invention, the reducing agent is selected from the group: coal, coke, char or petroleum coke. [0060] The reducing agent can significantly reduce the chrome spinel in the particulate chromite before it enters the molten slag phase at the base of a furnace.

[0061] In a preferred form of the invention, the reducing agent is combined with the particulate chromite and/or the silicon chain-based reagent in a quantity such that upon reaching pyrolysis temperature of the reducing agent, hydrogen, carbon and oxygen compounds are released to substantially reduce the chrome in the chromite

agglomerate.

[0062] There is good evidence that chromite agglomerates comprising a reducing agent of the present invention would be able to reduce chrome spinel to over 95% in less than 1 hour at approximately 1500 °C. See, for example, "The reduction of self - reducing chromite pellets at 1773 K - Intrapellet Temperature Gradients - Zambrano, Takano et al - IJRRAS 13 Oct 12, the contents of which are hereby incorporated by reference.

[0063] In one form of the invention, the silicon chain-based reagent comprises a compound of formula (I) dissolved in a solvent. In one form of the invention, the solvent may be selected from the group: water, alcohols, and mixtures thereof. In preferred forms of the invention, the alcohol is selected from the group methanol, ethanol, propanol and glycol and mixtures thereof.

[0064] Preferably, where the silicon chain-based reagent is not dissolved in a solvent, n is between 1 and 10.

[0065] In one form of the invention, where the silicon chain-based reagent comprises a compound of formula (I) dissolved in a solvent, the silicon chain-based reagent further comprises a surfactant. The surfactant may be ionic or non-ionic.

Examples can be from the following list of commercial products;

• MPM Silform range

• MPM EOF range

• Dow Corning Xiameter range

• Dow Corning Toray range

• Geleste bonding range • Zaclon LLC bonding range

[0066] In a preferred form of the invention, the viscosity of the silicon chain-based reagent is between 0.3 and 400 mPa.S at 20°C.

[0067] In preferred form of the invention the viscosity is between 50 and 200 mPa.S

[0068] In preferred form of the invention the viscosity is between 50 and 100 mPa.S

[0069] In a preferred form of the invention, the step of combining the particulate chromite with a silicone reagent to produce a silicon chain-based reagent-particulate chromite mixture more specifically comprises spraying the silicon chain-based reagent onto the particulate chromite. Preferably still, the step of combining the particulate chromite with a silicone reagent to produce a silicon chain-based reagent-particulate chromite mixture more specifically comprises spraying the silicon chain-based reagent onto the particulate chromite during mixing, moisture control, blending or conveying.

[0070] Dosages of the silicon-chain-based reagent per unit weight of particulate chromite can vary significantly depending upon the chemistry of the particulate chromite and the duty cycle required of the chromite granule product and can vary from 0.1 % by weight for light duty products to 20% for special ultra-high value products built to withstand extreme aggressive environments.

[0071] In a preferred form of the invention, the silicone based reagent comprises between 0.1 % and 20% of the silicon chain-based reagent-particulate chromite mixture. In a preferred form of the invention, the silicon chain-based based reagent comprises between 0.1 % and 10% of the silicon chain-based reagent-particulate chromite mixture. Preferably still, the silicon chain based reagent comprises between 0.5% and 5.0% of the silicon chain-based reagent-particulate chromite mixture. Further and still preferably, the silicon chain based reagent comprises between 1 .0% and 2.5% of the silicon chain-based reagent-particulate chromite mixture.

[0072] In one form of the invention the silicon chain based reagent comprises at least 2% of the silicon chain-based reagent-particulate chromite mixture. In one form of the invention the silicon chain based reagent comprises at least 2.5% of the silicon chain-based reagent-particulate chromite mixture. In one form of the invention the silicon chain based reagent comprises at least 3% of the silicon chain-based reagent- particulate chromite mixture. [0073] In one form of the invention, the step of combining the particulate chromite with a silicon chain-based reagent is undertaken at a temperature between -10 °C and 60 °C. More preferably, the step of combining the particulate chromite with a silicon chain-based reagent is undertaken at a temperature between 5 °C and 45 °C.

[0074] In a highly preferred form of the invention, the step of combining the particulate chromite with a silicon chain based reagent is undertaken at atmospheric pressure.

[0075] In a highly preferred form of the invention, the step of introducing the particulate chromite into an agglomeration apparatus to produce a chromite

agglomerate is undertaken at ambient temperature.

[0076] In a highly preferred form of the invention, the step of introducing the particulate chromite into an agglomeration apparatus to produce a chromite

agglomerate is undertaken at atmospheric pressure.

[0077] The method of the present invention involves mixing the selected silicon chain-based reagent with the particulate chromite which is then agglomerated utilising one or more agglomeration, granulation or pelletising apparatuses designed for this purpose.

[0078] In one form of the invention, the agglomeration apparatus is selected from the group: drum agglomerator, pan agglomerator, pug mixer, concrete mixer, blade and bar mixer, extruding device, conveyor belt mixer and granulator, tumbler, briquetting device, pressing device, belt roller, filter press agglomerator, manual agglomerator. In a preferred form of the invention, the agglomeration apparatus is a drum agglomerator.

[0079] Using the agglomeration apparatus described above in a conventional manner known to those skilled in the art, the method of the present invention can be utilised to create chromite agglomerates of any size required depending upon end use. For standard chromite smelting, the equipment would be configured to create a narrow size band of chromite agglomerates, which may be screened to produce highly regular chromite agglomerates.

[0080] An addition to providing a chromite agglomerate of sufficient strength to withstand smelting, the silicon chain-based reagents of the present invention enhance evaporation of contained moisture in the chromite agglomerate by enhanced capillary action to reduce inherent moisture to a very low level, ideally around 3-5% but can range between 1 % and 15% depending upon the end use of the product and the dosage of the silicon chain-based reagent

[0081] The present invention encompasses chromite agglomerates produced by any of the abovementioned methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which :

Figure 1 is a phase diagram showing the compositional range of the particulate chromites that are the subject of the method of the invention in terms of end- member components, being Mg, Fe, Cr, Fe, Al and O.

DESCRIPTION OF EMBODIMENTS

[0083] Further features of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above.

[0084] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0085] Experiments started with duplication of standard formula granulation were carried out with South African and Canadian chromite utilising bentonite clay, cement, lime, hematite clay, bauxite, fly ash and pozzalan in mixtures or alone up to 5% by weight. None of these combinations would work above a temperature of 800 °C, with the granules decrepitating and producing powder and or portions of the granules reaching liquidus and slagging. [0086] XRF and ICP (for CaO and S) analyses for the two chromites are as shown in Table 1 :

Table 1

[0087] Incremental dosages of between 0.5% and 10% in steps of 0.5% of the silicon chain-based reagent solution (30% by weight of the silicon chain based reagent - dimethyldichlorosilane, dimethyldiethylsilane and dimethyldiacetatesilane, polydimethyl siloxane, cyclopenta siloxane, trimethylated silica, tetra(trimethyl siloxy)silane, dodecamethylpenta siloxane in in solution) were added to 250 g batch samples of chromite concentrates sources from South African and Canadian chromite mining operations. The aim of the tests were to determine cold bonding performance for 12- 20mm chromite agglomerates in the form of granules for materials handling

performance and thermal stability to determine suitability for direct feed of the chromite granules to ferrochrome smelters without sintering.

[0088] The blended mixtures were granulated in a small drum agglomerator with a 4:1 diameter to length ratio with a variable speed drive to allow flexibility in producing different diameter granules, moisture content of the feed to the test agglomerator was between 12 and 20%. The samples were mixed with binding reagent prior to being placed into the granulation drum and makeup water added to suit the quality of the granules.

[0089] Dosage was varied from 0.5% through to 10% of silicon chain-based reagent by weight in steps of 0.5%, and the chromite granules cured for 21 days in ambient conditions (20°C +/- 2°C) and divided into 2 batches.

[0090] Compressive tests of the produced agglomerates was carried out on 10 agglomerates from each batch using a RB Automazione RB 1000 according to the ISO 4700 standard for "Cold Compressive Strength" testing criteria. The compressive strength of these cured ranged from 0.25kN to 0.65kN (acceptable compressive strength is greater than 0.5kN) and the moisture content varied between 2.5% and 4% [0091] The first batch of chromite granules were then tested for materials handling parameters, being dropped from 2m onto a steel plate 10 times, driven over by a vehicle 10 times and dropped into water for 8 hours and dried out for 21 days and physical tests above carried out. These tests model the materials handling environment of chromite pellets prior to introduction into a furnace.

[0092] The second batch were deposited in a muffle furnace starting at 600 °C and brought up to temperature increasing 100 °C every 30 mins up to the maximum of 1 100 degrees (the limit of the furnace) where the granules were left for 6 hours at 1 100 °C.

[0093] Samples with less than 2.0% silicone chain-based reagent by weight for both Canadian and South African chromites failed this test. Samples above this dosage in both cases passed the tests described above. The samples were then cooled inside the slowly cooling muffle furnace once it was turned off and the sample bagged for onward mineralogical analysis.

[0094] The results of the above trials showed that a combination of silicon chain - based reagent(s) mixed with particulate chromite can produce a hard, strong and thermally stable chromite agglomerate that will withstand temperatures sufficient for direct feed into the furnace without sintering induration.

[0095] The second phase of testing included modifying the testing parameters above and including a reducing agent in the form of petroleam coke. Experiments carried out Canadian and South African Chromites being a granulated a blend of;

chromite - 75% -(range from 50% to 90%) petroleum coke 18% (range 5% to 25%), quartz fume - 5%, (Range 0% to 20%) limestone 2% (Range 0% to 20%).

[0096] Baseline dosage of silicon chain-based reagent was started at 2.5% by weight of the silicon chain based reagent solution in steps of 0.5% up to 10% as in the non-reducing granules.

[0097] The granules were then subject to muffle furnace parameters as in the previous tests although it was noticed that at around 800°C a small blue flame halo was being produced around the shield of the granules (assuming carbon monoxide gas production) and this increased as the temperature increased and persisted for approximately 1 hour where the flame was no longer seen with exhaustion of the carbon source. [0098] Once again the granules were kept at 1100 °C for 6 hours and withdrawn for treatment with the reducing oxy-acetylene flame before being cooled.

[0099] Samples with less than 2% of the binding reagent by weight failed this cycle and the granules were much more porous than the non-reducing granules but had some slagging on the surface and were very hard with metallic flecks seen when granules were broken with a hammer.

[00100] The following tests were the successful outcomes or multiple tests carried out utilising binders targeted to bind with ores, concentrates and chrome containing wastes.

[00101] The following examples have been selected for illustrative purposes as these batches of pellets passed the drop test, drive over crush tests, rolling attrition and compressive strength tests described previously.

Example 1

Sinter Pellet Chemistry Cold Bond pellet

[00102] Agglomerates were prepared from a chrome spinel concentrate sourced from chromite and platinoid bearing orebodies in the Bushveld Complex in South Africa. The chrome spinel concentrate was measured to contain 52% Cr. The chrome spinel concentrate was mixed with bentonite clay and a silicon chain-based reagent binding solution. The silicon chain-based reagent binding solution consisted of the following reagents combined as blended bulk reagents added to the feedstock:

Tetramethlysilane -1 %;

Polydimethylsiloxane -2%;

Methoxysilane -1 %;

Methylglycolsiloxane -1 %;

Chrome (III) methacrylate -2%;

Diethylene glycol -6%; and

Water -87% as the reagent carrier. [00103] The blended mixtures were granulated in a small drum agglomerator.

Additional binding reagent was added to the granulation drum during balling and makeup water was added. The specifications of the mixture was as shown in Table 2:

Table 2

[00104] Total weight were measured as shown in Table 3:

Table 3

[00105] The above test produced 12,888 g of agglomerates with a size range from 10 mm to 22 mm.

[00106] The pellets then underwent desiccation in an open top tray which was exposed to air at ambient temperature with no fan ventilation. Average ambient conditions during the day were 26C with a humidity of 72 to 77%. Average ambient conditions during the night were 14C with a humidity of 64 to 66%. Desiccation took place for 21 days and the moisture loss was as shown in Table 4:

[The remainder of this page is left blank intentionally] Day Weight (g) Moisture loss (g/d) Cumulative Moisture loss (g)

0 12,788 0 0

1 12,451 337 337

2 12,207 244 581

3 11 ,884 323 904

4 11,820 64 968

5 11,768 52 1,020

6 11,710 58 1,078

7 11,666 44 1,122

8 11,631 35 1,157

9 11,598 33 1,190

10 11,568 30 1,220

11 11,548 20 1,240

12 11,534 14 1,254

13 11,521 13 1,267

14 11,514 7 1,274

15 11,510 4 1,278

16 11,508 2 1,280

17 11,506 2 1,282

18 11,504 2 1,284

19 11,504 0 1,284

20 11,504 0 1,284

21 11,504 0 1,284

Table 4

Compressive strength was an average of 0.65kN. Example 2

Sinter Pellet Chemistry Cold Bond pellet

[00107] Agglomerates were prepared from a chrome spinel concentrate sourced from the same location as in Example 1. The chrome spinel concentrate was measured to contain 52% Cr. The chrome spinel concentrate was mixed with bentonite clay, coal and a silicon chain-based reagent binding solution. The silicon chain-based reagent binding solution consisted of the following reagents combined as blended bulk reagents added to the feedstock:

Tetramethlysilane -1%;

Polydimethylsiloxane -2%;

Methoxysilane -1%;

Methylglycolsiloxane -1%; Chrome (III) methacrylate -2%;

Diethylene glycol -8%; and

Water -85% as the reagent carrier.

[00108] The blended mixtures were granulated in a small drum agglomerator.

Additional binding reagent was added to the granulation drum during balling and makeup water was added. The specifications of the mixture was as shown in Table 5:

Table 5

[00109] Total weight were measured as shown in Table 6:

Table 6

[001 10] The above test produced 9,393 g of agglomerates with a size range from 12 mm to 20 mm.

[001 11] The pellets then underwent desiccation in an open top tray which was exposed to air at ambient temperature with no fan ventilation. Average ambient conditions during the day were 27C with a humidity of 68 to 72%. Average ambient conditions during the night were 16C with a humidity of 60 to 66%. Desiccation took place for 21 days and the moisture loss was as shown in Table 7:

[The remainder of this page is left blank intentionally] Day Weight (g) Moisture loss (g/d) Cumulative Moisture loss (g)

0 9,393 0 0

1 9,245 148 148

2 9,143 102 250

3 9,036 107 357

4 8,935 101 458

5 8,840 95 553

6 8,743 97 650

7 8,650 93 743

8 8,561 89 832

9 8,471 90 922

10 8,405 66 988

1 1 8,345 60 1 ,048

12 8,291 54 1 ,102

13 8,275 16 1 ,118

14 8,262 13 1 ,131

15 8,251 11 1 ,142

16 8,248 3 1 ,145

17 8,245 3 1 ,148

18 8,242 3 1 ,151

19 8,242 0 1 ,151

20 8,242 0 1 ,151

21 8,242 0 1 ,151

Table 7

Compressive strength was an average of 0.55kN. Example 3

Chromite & Ferro-Chrome EAF dust - furnace ready pellet

[001 12] Agglomerates were prepared from a chrome spinel concentrate sourced from the same location as in Example 1 . The chrome spinel concentrate was measured to contain 52% Cr. The chrome spinel concentrate was mixed with bentonite clay and ferro-chrome EAF dust @17% Cr filter cake, along with a silicon chain-based reagent binding solution. The silicon chain-based reagent binding solution consisted of the following reagents combined as blended bulk reagents added to the feedstock:

Tetramethlysilane -1 %;

Polydimethylsiloxane -2%;

Methoxysilane -1 %;

Methylglycolsiloxane -1 %; Chrome (III) methacrylate -2%;

Diethylene glycol -10%; and

Water -83% as the reagent carrier

[001 13] The blended mixtures were granulated in a small drum agglomerator.

Additional binding reagent was added to the granulation drum during balling and makeup water was added. The specifications of the mixture was as shown in Table 8:

Table 8

[001 14] Total weight were measured as shown in Table 9:

Table 9

[001 15] The above test produced 1 1 ,420 g of agglomerates with a size range from 9 mm to 16 mm.

[001 16] The pellets then underwent desiccation in an open top tray which was exposed to air at ambient temperature with no fan ventilation. Average ambient conditions during the day were 29C with a humidity of 65 to 70%. Average ambient conditions during the night were 17C with a humidity of 58 to 62%. Desiccation took place for 21 days and the moisture loss was as shown in Table 10:

[The remainder of this page is left blank intentionally] Day Weight (g) Moisture loss (g/d) Cumulative Moisture loss (g)

0 11 ,420 0 0

1 11,175 245 245

2 10,950 225 470

3 10,780 170 640

4 10,635 145 785

5 10,505 130 915

6 10,399 106 1,021

7 10,310 89 1,110

8 10,255 55 1,165

9 10,221 34 1,199

10 10,202 19 1,218

11 10,186 16 1,234

12 10,179 7 1,241

13 10,173 6 1,247

14 10,170 3 1,250

15 10,169 1 1,251

16 10,168 1 1,252

17 10,168 0 1,252

18 10,168 0 1,252

19 10,168 0 1,252

20 10,168 0 1,252

21 10,168 0 1,252

Table 10

Compressive strength was an average of 0.52kN, Example 4

Ferro-Chrome EAF dust - furnace ready pellet

[00117] Agglomerates were prepared from a ferro-chrome EAF dust containing 17% Cr filter cake. The ferro-chrome EAF dust was mixed with bentonite clay and a silicon chain-based reagent binding solution. The silicon chain-based reagent binding solution consisted of the following reagents combined as blended bulk reagents added to the feedstock:

Tetramethlysilane -1%;

Polydimethylsiloxane -2%;

Methoxysilane -1%;

Methylglycolsiloxane -1%; Chrome (III) methacrylate -2%;

Diethylene glycol -10%; and

Water -83% as the reagent carrier.

[001 18] The blended mixtures were granulated in a small drum agglomerator.

Additional binding reagent was added to the granulation drum during balling and makeup water was added. The specifications of the mixture was as shown in Table 11 :

Table 11

[001 19] Total weight were measured as shown in Table 12:

Table 12

[00120] The above test produced 8,470 g of agglomerates with a size range from 12 mm to 18 mm.

[00121] The pellets then underwent desiccation in an open top tray which was exposed to air at ambient temperature with no fan ventilation. Average ambient conditions during the day were 29C with a humidity of 65 to 70%. Average ambient conditions during the night were 17C with a humidity of 58 to 62%. Desiccation took place for 21 days and the moisture loss was as shown in Table 13: Day Weight (g) Moisture loss (g/d) Cumulative Moisture loss (g)

0 8,470 0

1 8,344 126 126

2 8,228 1 16 242

3 8,128 100 342

4 8,036 92 434

5 7,951 85 519

6 7,866 85 604

7 7,785 81 685

8 7,708 77 762

9 7,648 60 822

10 7,592 56 878

1 1 7,544 48 926

12 7,509 35 961

13 7,485 24 985

14 7,480 5 990

15 7,478 2 992

16 7,475 3 995

17 7,474 1 996

18 7,472 2 998

19 7,472 0 998

20 7,472 0 998

21 7,472 0 998

Table 13

Compressive strength was an average of 0.62kN.

[00122] Following the above trials, it was determined that a silicon chain-based reagent binding solution which would be applicable to the majority of chromite containing ores consists of the following reagents combined as blended bulk reagents added to the feedstock:

Tetramethlysilane -1 %;

Polydimethylsiloxane -2%;

Methoxysilane -1 %;

Methylglycolsiloxane -1 %;

Chrome (III) methacrylate -2%;

Diethylene glycol -10%; and Water -83% as the reagent carrier.

[00123] It is envisaged by the applicant that whilst the above blend is applicable to most chromite containing ores, that the mineralogy of the particular feedstock will require different blends.

[00124] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.