METHOD FOR PREPARING HARDENED GRANULES FROM A

PARTICULATE MATERIAL

TECHNICAL FIELD

The invention relates to a method for preparing hardened granules from a particulate material which comprises admixing to the particulate material an aqueous inorganic binder, converting the resulting moist mixture into granules and hardening said granules. The invention also relates to new uses of granules thus prepared and to novel granulates for such uses. BACKGROUND ART

US-A-4917732 discloses a process whereby fly ash and slag from gasification of coal are combined to produce a composite which may be used in road construction.

EP-A-0 346 992 discloses a process for manufacturing a hardenable mixture containing coal ash and fly ash which is essentially free of CaO CaSO ₄ .0H ₂ O and a building component made from a hardenable mixture.

EP-A-0 152 637 discloses a method of forming granules wherein the granules are heated by means of heat provided by slaking calcium oxide. The obtained granules are envisaged to be used as an aggregate for concrete.

EP-A-0 296 621 discloses a method for producing hard granules from an ash comprising a coal ash and used desulphurizing agent which granules are ground to obtain a high CBR value by pulverizing them. The ground material thus obtained may have effective utilization as a material in the civil engineering and construction industry.

EP-A-0 301 661 discloses granulating and hardening of a mixture of an inorganic binder, water and fly ash.

EP-A-0 038 599 discloses production of a granulated material comprising a filler possessing

latent hydraulic properties and an inorganic binder, for use as additive in concrete.

In the prior art relatively low grade particulate materials such as fly ash are processed in order to dispose of them. The processed materials are used as land filling or for road building and construction purposes.

EP-A-0499779 discloses a process for treatment of a metal containing mixture of solid and liquid waste streams, the mixture occurring in a condition in which it can not be used or only with difficulty, by admixing fly ash and / or coke dust to an extent to form dry agglomerates having a grain size of up to 4 mm that can be recycled in a metallurgical process or for cement manufacture. According to EP-A-0499779 if fly ash having pozzolanic properties is used the mixture can be pelletized and the pellets so obtained can be hardened to give them the level of strength required for the metallurgical process, or the mixture can be briquetted. DISCLOSURE OF THE INVENTION

It has now been found surprisingly that when applying certain process conditions to materials comprising ingredients suitable as a raw material or an agent in a chemical or physical process, these can be converted into hardened granules which can be advantageously used as an active feed stock component in such a chemical or physical process.

The present invention provides a method as set out in the opening paragraph which is characterised in that it comprises the stepε of

(i) selecting a particulate material comprising ingredients suitable as a raw material or an agent in a selected chemical or physical process;

(ii) were applicable bringing the particulate material to a particle size distribution suitable for aggregation into granules;

(iii) composing and mixing a mixture comprising

the particulate material; - an aqueous inorganic binder selected from the group consisting of a calcareous binder, cementitious binder, hydraulic cement, Portland cement, high alumina cement, a mixture of a source of calciumhydroxide with a source of silica, lime, gypsum and dolomite; bringing about a moisture content so that a granulatable mixture is obtained;

(iv) forming granules; (v) hardening said granules at a temperature above room temperature and below the boiling temperature of the moisture whilst sticking together of the granules is avoided and where applicable excess moisture from the granules is extracted; (vi) withdrawing the hardened granules in the form of a feed stock component for said selected process. The particulate material to be processed according to the invention is a raw material suitable to be used as feed stock in e.g. a high temperature industrial process. The particulate material can be a partly pyrolysed material, including for example a gasification residue from the gasification of carbonaceous solids such as black coal, lignite (brown coal) or wood. Other particulate materials are organic carbonaceous material like chars from various sources, wood charcoal, activated carbon from the partial combustion of coca-nut shells or the like, and coke, in particular derived from black coking coal, etc. and also anorganic fine materials like base metal containing ore, furnace dust, residues from recycling processes, dust from bulk materials handling in terminals, harbours, industries, etc. The invention is also applicable to pretreated and upgraded residues, where pretreatment of wet and or coarse material takes place by drying and/or crushing,

milling, etc. in order to obtain a fine product for further treatment and upgrading is obtained by increasing the carbon content thereof and/or reducing the content of harmful contaminants, for example phosphorus, sulphur, heavy metals or other specific components.

However, with respect to carbonaceous material the invention is not limited to pyrolysed, partly pyrolysed or natural carbonaceous substances, but extends to carbonaceous particulate materials selected from the group consisting of bituminous black coal, sub- bituminous black coal, brown coal, coal fines, coke, char, anthracite, wood derived charcoal, gasification residue, activated carbon, carbon black and duff coal, as is and after upgrading.

The metallic and/or metalliferous material can be fines from the mining or handling of ferrous metal ores, heavy metal ores, mill scale, foundry dust, dust from metallurgical flue gas cleaning systems, and carry-over material from metallurgical processing slags from metallurgical processes such as titanium slag, or metal oxides, reducible metal ores, chromite ores, ferromanganese ores, ferrous titanium ores, ferrous vanadium ores, hematite, magnetite, limonite, rutile, baddeliyte and other zirconium oxide ores, sulfidic ores.

The particulate material can also be a mixture of carbonaceous and metalliferous materials.

The combination of metalliferous and carbonaceous materials in a granule gives distinct advantages when combined with the low temperature hardening employed. By feeding such a combination into a metallurgical furnace the ore and the reductant can be placed together in the heat zone of the furnace which yields higher metal recovery rates with higher carbon efficiency.

Preferably the particulate material to be used in step (iii) is provided having a moisture content of

lower than 15 % by weight.

Preferably, in cases where the granules are metalliferous, for use in a thermal metallurgical process and where the granules contain from 0 up to 20 % by weight of combustible carbon, the crushing strength of the hardened granules withdrawn is not less than 3

N/mm ² , preferably from 5 N/mm ² up to about 7 N/mm ² , and more particularly 6 N/mm ² .

In a preferred embodiment of the invention the source of calciumhydroxide expressed as calcium oxide is: between 2 and 12 % weight by weight of the particulate material, more preferably between 4 and 10 % weight by weight of the particulate material, most preferably

- between 6 and 8 % weight by weight of the particulate material. The source of silica used to obtain the desired reactions is a silicon containing composition like sodium silicate, magnesium silicate or another silicon compound with the ability to release silica in the presence of calcium hydroxide.

The amount of the silicon containing composition required for the desired reactions with the source of calciumhydroxide expressed as silica is: between 1 and 6 % weight by weight of the particulate material, more preferably between 2 and 5 % weight by weight of the particulate material, most preferably - between 2 and 4 % weight by weight of the particulate material. Preferably more than 90 % of the particulate material is in the overall particle size range of 5 to

2000 μm, more preferably at least 50 % is in the overall particle size range of 100 to 1000 μm. In case of a coarser material the indicated preferable grainsize can be achieved by crushing and milling.

The source of calcium hydroxide may be calς.ium oxide, lime, latent hydraulic components which produce calcium hydroxide when mixed with water, gypsum and calcined dolomite, which may optionally be partly or wholly slaked.

According to further preferred features of the invention there is provided between the steps of forming the granules and hardening the granules the further step of applying a coating material to form coated granules. In a further embodiment according to the invention the method comprises during the step of hardening the granules embedding the granules in an embedding material suitable for avoiding sticking together of the granules and extracting excess moisture from the granule where applicable. The coating material may be the same material as the embedding material. Preferably the coating and/or the embedding material has a water absorption capacity of at least 8 % by its own weight, more preferably of at least 10 %, most preferably of between 15 and 25 %.

In another embodiment of the invention at least 80 % of the coating and/or the embedding material is in the overall particle size range of 2 to 1200 μm and at least 90 % is smaller than 2000 μm. Preferably the coating and/or the embedding material is the particulate material itself, or another powdery material from coal combustion, gasification, etc.

Where coating and/or embedding is merely applied in order to further hardening and obviate sticking together of the granules in a bulk hardening step, it may be advantageous to include a step (vii) of substantially removing the coating and/or embedding material from the granules e.g. by mechanical abrasion. It is possible to recycle used coating and/or embedding material by drying it to a moisture content of lower than 5 % by weight after it is separated from the

hardened granules.

A further aspect of the invention when the particulate material is a carbonaceous material is the use of the hardened granules as a fuel, as a reducing agent, as a gasification raw material, as a carbide production raw material or as an absorbent in a physical process. The use of upgraded carbonaceous residues, in the said granules as a reducing agent, is of importance in the reduction of base metals, for example ferrous metals and other base metals products, but in particular in the industries where low levels of contaminants like phosphorus and sulphur is of the utmost importance.

The carbonaceous and metalliferous granulates may in particular be used as feed stock in a high temperature chemical or metallurgical process.

Carbonaceous granules of high carbon and low volatiles content are suitable as a low cost smokeless fuel, e.g. for domestic heating and cooking. Physical processes include adsorption processes for which purpose the carbonaceous component may be activated or reactivated in manners known per se.

Another aspect of the invention is the processing of dust from gas cleaning systems, carry-over material, foundry dust, dust from ore handling etc. into granules which can advantageously be used to extract metals.

Herewith an interesting industrial application of these dusty materials is achieved.

The invention is also embodied in a granulate for use as feed stock in a selected chemical or physical process comprising a binder from the group consisting of a calcareous binder, cementitious binder, hydraulic cement, Portland cement, high alumina cement, a mixture of a source of calciumhydroxide with a source of silica, lime, gypsum and dolomite and an ingredient suitable as a raw material or an agent in said process selected from the group consisting of combustible carbonaceous materials, metallic or metalliferous materials.

Granules of a spherical form with a size of not less than 8 mm comprising carbonaceous and metalliferous materials are advantageously used in a metallurgical process as elements to form a packed bed and assist in giving the bed the required structure since a compressive strength of more than 4.8 N/mm ² is obtainable when complying with certain aspects of the invention, as exemplified in the examples.

A raw material or an agent in the form of a granulate preferably having a spherical form and size of from 8 to 35 mm can be handled and dosed easily. According to the invention in an aspect the granulate comprises a substantial amount of carbon of more than 25 % by weight and/or of a metal in metallic or metalliferous form of more than 10 % by weight expressed as the metal and has a hardness in the range of 3 - 10 N/mm ² .

The hardness is sufficient not to crush under normal handling conditions. On the other hand the hardness is not as high as that of sintered pellets. An interesting feature of the invention is that the granulate is obtained by hardening at a temperature as low as below 150 °C. This has the additional benefit that no or only limited oxidizing occurs during hardening.

The invention will now be described in some aspects. BEST MODE FOR CARRYING OUT THE INVENTION

In case of wet and/or coarse material a pretreatment step comprising of drying, crushing or milling will be required to achieve a processable material.

An installation as for carrying out the method according to the invention comprises a mixer, receiving the particulate material from a material supply hopper, a calcium oxide from a supply hopper, a silicate composition from supply hopper, water from a water

supply container and optionally other components from a miscellaneous supply hopper. The materials are premixed in a screw conveyor and dosed in a high speed, high shear mixer, where the above mentioned components are intensively mixed to obtain the desired homogeneous composition.

This composition is then transported to a rotating granulator. Granules of spherical form produced in the granulator are deposited upon a belt together with a dry material for embedding.

The embedded granules are then conveyed into a hardening reactor. By means of steam the temperature of the embedded granules is elevated to the desired temperature. After hardening, hardened granules are obtained by separating the granules from the embedding material by means of a screen. The embedding material can be recycled into the process if it is the same particulate material or re-used for embedding after drying. The invention is furthermore illustrated by means of the following examples.

Example I

Carbonaceous residue from a gasification process as the particulate material, having a carbon content of 45 % and a moisture content of 52,5 %, was dried to a moisture content of 14 % and mixed with 7 % of lime as binder and 3 % sodium silicate as additive. These materials were firstly premixed and then, under the addition of water, intensively mixed in a high intensity mixer. This resulted in a so-called green mix. The green mixture had a moisture content of 24,3 % and a pH of 12,2.

The green mix was then converted to granules in a granulator. The moisture content of the resultant green granules was 27,5 %.

The green granules were embedded in the same but

dried carbonaceous residue with a moisture content of 3 % as the embedding material and transported to a curing silo in which they were heated up by dosing of steam. Curing took place at 100 % relative humidity at a temperature of about 85 °C for 20 hours.

After curing the material was screened and the embedding material recovered for use to produce green pellets. In another test the same was repeated, however the embedding material was dried after screening and used again as embedding material. In another test the green pellets were embedded in coal fly-ash, which was dried for re-use as embedding material.

The resultant granule strength measured for granules of a mean grain size φ 10 mm in all these cases was 6,2 N/mm ² , ± 10 %.

Alternative investigated binders to process this residue include binders like cement and bentonite in quantities of between 2 and 10 %. Granules strengths then obtained were in the range from 0,6 N/mm ² to 1,2 N/mm ² .

Example II

Example I is repeated, however now instead of the high intensity mixer a conventional mixer of the type normally used for mixing concrete components was used. All other features of the process were carefully held the same. The resultant granules strength was now 2,3 N/mm ² measured for φ 10 mm granules.

Example III

Example I was repeated with 4 % lime addition as binder and the resultant granule strength, size φ 10 mm, was 1,6 N/mm ² .

Example IV

The procedure of example I was repeated without however adding any additive. A granule strength of 2,5

and 3,0 N/mm ² (size φ 10 mm) was obtained.

Example V

Example I is repeated with upgraded gasifier residue as the particulate material having a carbon content of 75 % and a moisture content of 42,7 % as a raw material. Prior to processing the particulate material was dried to a moisture content of 14 %. The resultant granules strength was 7,2 N/mm ² (size φ 10 mm) .

Example VI

Example I is repeated using anthracite as the particulate material. The anthracite fines have a carbon content of 85 % and a moisture content of 30 %. Prior to processing the material was dried to a moisture content of 14 %.The resultant granules strength was 6,5 N/mm ² (size φ 10 mm) .

Example VII Example I is repeated using coal particles and fines with a size distribution of 0,5 - 200 mm as the particulate material and embedding material. Prior to processing the material was crushed and ground to particles smaller than 2 mm. The resultant granules strength was 6,3 N/mm ² (size φ 10 mm) .

Example VIII

Fines from iron ore resulting from transport and handling of the ore were processed as the particulate material according to the same method as example I, using both fine ore and coal fly-ash as embedding material. The resultant granules strength was 5,9 N/mm ² (size φ 10 mm) .

Example IX

Example I was repeated however now a chromium ore was used as the particulate material for producing the

granules .

The resultant granules strength was 6,1 N/mm ² (size ø 10 mm) .

Example X

Example I was repeated however now an iron ore dust and fine coke mixture was used as the particulate material to produce the granules.

The resultant granules strength was 4,8 N/mm ² (size φ 10 mm) .

Example XI

Example I is repeated however now a mixture containing of equal amounts of chromium dust and fine coal was used as the particulate material to produce the granules.

The resultant granules strength was 6,0 N/mm ² (size ø 10 mm) .

Example XII

Trials with coke breeze granules were performed in a furnace for the reduction of iron ore. Coke, normally used as reductant was replaced by coke breeze granules obtained according to the invention. The amount of used was based on the equivalent carbon content. The recoveries achieved with the coke breeze were more than 95 % which is equal to normal recoveries achieved with coke. The coke breeze remain their strength at the high temperatures and therefore proved to be an excellent carrier for the iron ore in the furnace.

Example XIII

The above trials were repeated however now coal fines were used instead of coke breeze granules. Recoveries achieved were similar to the earliest tests. At temperatures higher than 900 °C, the coal granules lost some of their strengths and therefore it is in this

case advisable to replace only a part, e.g. _50 % of the coke or coke breeze pellets by coal pellets.

Example XIV The above mentioned test was repeated however now the coke was replaced by coke breeze granules and the iron ore was replaced by granules produced with iron ore dust. Recoveries achieved were more than 95 %. Two waste materials from the iron and steel industry (coke breeze is a waste material from the coke factory) and iron ore dust (dust of filters from handling and processing of iron) are combined to produce iron.

Example XV The above mentioned test was repeated but now copper ore dust was used for the production of granules. These granules together with coke breeze granules were successfully used for the production of copper.

Example XVI

Granules produced according to the invention using as the particulate material a high carbon residual material with a carbon content of 76 % and as the binder 6 % lime, were used as an adsorbent for removing organic components from an industrial effluent. The granules were capable of removing 33 % of the impurities from the effluent.

Example XVII Trials were conducted to evaluate the performance of a carbon containing granulate (67 % C) prepared according to the invention as reductant in a process to recover chrome from chrome ore, as compared to that in the known process using normal cokes as the reductant. The chrome recovery was 76,1 % when using the granulate according to the invention and 71-74 % when using conventional coke reductants. Carbon efficiency when

using said granulate was 77.9 % versus a previous best of 76.3 % on the particular furnace with conventional coke reductant.

The contents of the priority documents and of the following claims form part of the present disclosure.