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EP1360339A1 - Liants de silicate contenant un agent de durcissement a base de calcium - Google Patents

Liants de silicate contenant un agent de durcissement a base de calcium

Info

Publication number
EP1360339A1
EP1360339A1 EP02710140A EP02710140A EP1360339A1 EP 1360339 A1 EP1360339 A1 EP 1360339A1 EP 02710140 A EP02710140 A EP 02710140A EP 02710140 A EP02710140 A EP 02710140A EP 1360339 A1 EP1360339 A1 EP 1360339A1
Authority
EP
European Patent Office
Prior art keywords
curing agent
weight
alkali metal
silicate
per cent
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02710140A
Other languages
German (de)
English (en)
Inventor
Jennifer Emma Nicholls
David Peter Carter
Robert Macdonnell Hunter
Mfanafuthi Shadrack Nkutha
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ineos Silicas Ltd
Original Assignee
Ineos Silicas Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ineos Silicas Ltd filed Critical Ineos Silicas Ltd
Publication of EP1360339A1 publication Critical patent/EP1360339A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B34/00—Obtaining refractory metals
    • C22B34/30—Obtaining chromium, molybdenum or tungsten
    • C22B34/32—Obtaining chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/24—Binding; Briquetting ; Granulating
    • C22B1/242—Binding; Briquetting ; Granulating with binders
    • C22B1/243—Binding; Briquetting ; Granulating with binders inorganic

Definitions

  • This invention relates to the use of alkali metal silicates for binding or agglomerating particulate material and, in particular, to the use of alkali metal silicates in combination with a curing agent to bind particulate material.
  • the block making process comprises mixing the mineral fines with a binder, forming the mixture produced into a block, compacting under pressure and/or consolidating by vibrating in a mould, demoulding and then allowing the blocks to harden at ambient temperature so that the blocks are hard and do not break easily after 24 hours.
  • the most commonly used binder for the blocking of chrome ore fines is cement because it allows the blocks to be shaped before they set.
  • the use of cement is, however, undesirable because the amount of cement used leads to a decrease in the productivity of a smelting furnace and impurities introduced with the cement (such as sulphur and phosphorus) can affect the quality of metal eventually produced from the ore.
  • Sodium silicate has been evaluated as an alternative binder in place of cement in the blocking of chrome fines. The result has been unsatisfactory due to the poor green strength of the blocks produced and the extended time period required for the curing of the blocks at temperatures between 20° C to 50° C.
  • a method wherein a silicate can be employed in an efficient agglomerating process at ambient temperatures or just above has now been devised. The process can provide a delayed setting time, enabling bodies to be readily shaped and the bodies produced have a good green strength.
  • a method of binding the particles of a particulate material comprises preparing a composition comprising the particulate material, an alkali metal silicate and a curing agent, forming said composition into a shaped body and allowing said mixture to cure so as to form a rigid shaped body, wherein said curing agent is a composition comprising an intimate mixture of calcium carbonate and calcium oxide in which the calcium oxide comprises from 10 to 90 per cent by weight of the intimate mixture.
  • the calcium oxide and calcium carbonate are present as an intimate mixture and the curing agent is believed to be more effective in controlling the reaction rate of the alkali metal silicate if the curing agent comprises particles which contain both calcium oxide and calcium carbonate rather than consisting of a mixture of particles of calcium oxide and particles of calcium carbonate.
  • curing agent which can be employed in this invention is the by-product dust formed during calcination of limestone.
  • a proportion of the lime becomes entrained in the exhaust gases and must be removed therefrom, typically by means of bag filters, wet scrubbers, electrostatic precipitators or gravel bed filters.
  • the composition of this dust depends upon the conditions under which it was produced and the composition of the limestone used in the kiln.
  • the major component is usually calcium oxide (lime) but, in view of exposure of the dust to carbon dioxide in the exhaust gases, a further significant component is calcium carbonate.
  • sulphate usually in the form of calcium sulphate is present and the major non-calcareous contaminants are compounds of silicon and aluminium, probably derived from clay which is present in the limestone.
  • the curing agent contains from 20 to 80 per cent by weight calcium oxide and, more preferably, from 30 to 70 per cent by weight calcium oxide.
  • the curing agent contains at least 5 per cent by weight calcium carbonate and more preferably at least 15 per cent calcium carbonate. Generally, not more than 40 per cent by weight calcium carbonate is present.
  • the curing agent is preferably a finely divided solid and preferably it has a weight mean particle size below 100 ⁇ m, as determined by Malvern Mastersizer, using the method detailed hereinafter. More preferably, the curing agent has a weight mean particle size below 50 ⁇ m and a weight mean particle size below 25 ⁇ m is even more preferable. Usually, the curing agent will have a weight mean particle size above 5 ⁇ m.
  • any alkali metal silicate can be used in the process of the invention but sodium or potassium silicates are preferred and, generally, sodium silicate is more economical to use. Alkali metal silicates are available with a range of silicate to alkali metal ratios and, in general, silicates having any ratio are suitable for use in the invention.
  • a silicate having a molar ratio of Si0 2 to M 2 0, where M is an alkali metal, above 1.6 is preferred since such silicates are generally cheaper and are less corrosive than those having a lower Si0 2 to M 2 0 molar ratio.
  • the molar ratio, Si0 2 to M 2 0 is in the range 1.6 to 3.3. More preferably, the ratio is in the range 1.6 to 2.6 and, even more preferably, is in the range 1.8 to 2.3.
  • the alkali metal silicate can be employed in any suitable form.
  • Aqueous solutions having a range of concentrations and a range of Si0 2 : M 2 0 ratios are readily available commercially and these are convenient for use in this invention. Generally, these solutions will have a solids content in the range 35 to 55 per cent by weight, expressed as weight of Si0 2 plus M 2 0. More preferably, the solids content is in the range 40 to 50 per cent by weight, expressed as Si0 2 plus M 2 0.
  • a wide range of proportions of alkali metal silicate to curing agent can be used.
  • the ratio of silicate to curing agent is in the range 1 : 1 to 10 : 1 by weight and, preferably, the ratio of silicate to curing agent is in the range 1.5 : 1 to 7 : 1 , the silicate being expressed as weight of Si0 2 plus M 2 0 present.
  • the particulate material which can be agglomerated using the silicate and curing agent.
  • Typical particulate materials include powdered coal, crushed ores, particulate waste products, ferrochrome, silicon carbide, tailings from precious metal extraction and waste from the steel industry.
  • One particularly useful embodiment of the method of the invention is the formation of agglomerated masses of ore particles which, in the non-agglomerated form, are too small to process effectively.
  • the method of the invention has been found to be particularly useful in the recovery of small particles of chrome-bearing ores, particularly chromite ores, which would normally severely affect the efficiency and safe operation of the smelting furnace during processing, because of their size.
  • the particles which are agglomerated using alkali metal silicate and curing agent when applied to such small particles, usually have a very wide range of particle size.
  • the method is suitable for agglomerating material containing particles ranging in size from about 0.5 ⁇ m to about 30 mm.
  • the particulate material prefferably has a low water content and preferred particulate material contains less than 5 per cent water by weight.
  • the rigid shaped bodies which are formed using the method of the invention may take any suitable form.
  • the method can, for example, be used to produce granules or pellets in a granulator or pelletiser or to produce moulded or extruded bodies of any desired shape.
  • the rigid bodies are blocks or bricks and these blocks are particularly preferred in the recovery of small particles of chrome ores.
  • a pre-mix of the dry, particulate ore and the curing agent is first prepared.
  • the alkali metal silicate solution is usually mixed in proportions which provide from 1.0 to 4.5 parts, preferably from 1.5 to 3.5 parts, by weight of an alkali metal silicate expressed as weight of Si0 2 plus M 2 0 present and from 0.25 to 2.0 parts, preferably from 0.5 to 1.5 parts by weight of the curing agent with respect to 100 parts by weight of the particulate ore, expressed as dry weight.
  • the resultant mixture is transferred to a mould, compacted, demoulded and allowed to cure to form the rigid body. Usually, the mixture will cure at ambient temperature, but slight heating can accelerate the process.
  • the mixture is usually cured at a temperature in the range 15 to 65° C.
  • the blocks will be sufficiently hard to use after a curing period in the range 20 to 24 hours.
  • the cured blocks preferably have an unconfined compressive strength of at least 1 MPa.
  • the blocks have an unconfined compressive strength up to 3 MPa.
  • Weight Mean Particle Size The weight mean particle size of materials used in this invention is determined using a Malvern Mastersizer model S, with a lens range up to 300 mm RF and MS1 sample presentation unit.
  • This instrument made by Malvern Instruments, Malvern, Worcestershire, uses the principle of Mie scattering, utilising a low power He/Ne laser. Before measurement the sample is dispersed in isopropanol for 1 minute using a 3000 rpm stirrer to form a suspension. This suspension is stirred before and whilst it is subjected to the measurement procedure outlined in the instruction manual for the instrument, utilising the 300 mm RF lens range in the detector system.
  • the Malvern Mastersizer measures the particle size distribution of the inorganic material based on the volume of the particles.
  • the weight mean particle size (d 50 ) or 50 percentile is readily obtained from the data generated by the instrument. Green Strength
  • the method of the invention provides an economical means of binding together particulate material to form agglomerates which are non-dusty and can be easily handled.
  • the rate of cure of the agglomerates is such that the initial mixture can be prepared and formed into an appropriate shape before setting, but the body has an adequate green strength to allow demoulding after a short period and a sufficiently strong rigid body is produced in a reasonable time.
  • the curing agent used in this example was a by-product from a lime calcination process. It was recovered from the electrostatic precipitators used to remove dust from the exhaust gases on a South African lime calciner.
  • the principal components of this material were as follows (weight percentages); the calcium content is a measure of the CaO, Ca(OH) 2 and CaC0 3 present : calcium (as CaO) 66.5% silicon (as Si0 2 ) 13.0% aluminium (as Al 2 0 3 ) 7.4% iron (as Fe 2 0 3 ) 1.9% magnesium (as MgO) 1.8% sulphur (as S0 3 ) 0.5% titanium (as Ti0 2 ) 0.4% manganese (as MnO) 0.3%
  • the loss on ignition (1250° C to constant weight) was 7.4% by weight. This sample was estimated to contain 22.2 % CaC0 3 by weight.
  • Example 2 Small scale agglomerated blocks were prepared as follows, using fine particulate chromite ore as used in current block-making processes employed in South Africa. This ore contained 3% moisture by weight.
  • a dry mixture of 100 parts chromite ore and 1.5 parts of the curing agent used in Example 1 was prepared by blending in a beaker with a spatula. 5 parts by weight of sodium silicate solution, molar ratio of Si0 2 to Na 2 0, 2.1 , solids content, 48.2 per cent by weight, was added to this mixture and quickly stirred in with a spatula.
  • This resultant mixture was transferred to a cylindrical mould 32 mm diameter which was standing on a base plate. The mixture was consolidated within the mould using an appropriately sized ram and a light mallet. The moulded cylindrical block (32 mm diameter x approximately 35 mm high) was then removed from the mould and allowed to cure overnight at room temperature.
  • the unconfined compressive strength (UCS) was measured using a Zwick Universal Testing Machine Type No. Z030, 24 hours after the block was prepared. Two blocks were tested and found to have a mean UCS of 1.33 MPa with a standard deviation of 0.32 MPa.
  • Cylindrical blocks were prepared in a similar manner to that described in Example 2, except that the chromite ore was dried in an oven at 105° C until it contained an undetectable amount of water and the blocks were cured with 5 weight parts of 2.5 molar ratio silicate solution having a solids content of 46J per cent by weight and 0.5 weight parts of the same curing agent as used in Examples 1 and 2 per 100 weight parts chromite ore.
  • the mean UCS after 24 hours was 4.36 MPa with a standard deviation of 0.64 MPa on 4 samples.
  • Fine chromite ore was mixed with the curing agent used in Example 1 in the ratio 100 parts ore to 0J5 parts curing agent by weight.
  • 3.5 parts by weight sodium silicate solution having a molar ratio of 2.5 : 1 , Si0 2 to Na 2 0, was added to the ore/curing agent mix with stirring and the resultant mixture formed into blocks as described in Example 2 above.
  • the Green Strength was measured using the test described hereinbefore. The percentage of fines after testing was 28 per cent for blocks made according to this example and 70 per cent for blocks made without any curing agent.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Metallurgy (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • Geochemistry & Mineralogy (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Silicates, Zeolites, And Molecular Sieves (AREA)
  • Curing Cements, Concrete, And Artificial Stone (AREA)

Abstract

L'invention concerne un procédé permettant de lier les particules composant un matériau particulaire. Ce procédé consiste à préparer une composition comprenant ce matériau particulaire, un silicate de métal alcalin et un agent de durcissement, à former cette composition de manière à produire un corps façonné rigide. L'agent de durcissement est une composition contenant un mélange intime de carbonate de calcium et d'oxyde de calcium, l'oxyde de calcium représentant de 10 à 90 pour-cent en poids de ce mélange intime. Ce procédé est utile pour l'agglomération de matériaux en particules fines, en particulier dans les industries extractives. Le minerai de chromite en particules fines constitue un exemple d'application caractéristique.
EP02710140A 2001-02-12 2002-01-31 Liants de silicate contenant un agent de durcissement a base de calcium Withdrawn EP1360339A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB0103278A GB0103278D0 (en) 2001-02-12 2001-02-12 Silicate binders
GB0103278 2001-02-12
PCT/GB2002/000430 WO2002064846A1 (fr) 2001-02-12 2002-01-31 Liants de silicate contenant un agent de durcissement a base de calcium

Publications (1)

Publication Number Publication Date
EP1360339A1 true EP1360339A1 (fr) 2003-11-12

Family

ID=9908459

Family Applications (1)

Application Number Title Priority Date Filing Date
EP02710140A Withdrawn EP1360339A1 (fr) 2001-02-12 2002-01-31 Liants de silicate contenant un agent de durcissement a base de calcium

Country Status (4)

Country Link
EP (1) EP1360339A1 (fr)
GB (1) GB0103278D0 (fr)
WO (1) WO2002064846A1 (fr)
ZA (1) ZA200305964B (fr)

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2205043A (en) * 1937-11-17 1940-06-18 George S Mican Iron oxide briquette
JPS53104514A (en) * 1977-02-25 1978-09-11 Akira Konishi Method of reusing dust produced in producing ferrosilicon
GB1600711A (en) * 1977-06-22 1981-10-21 Midrex Corp Briquet and method of making same
GB2028787B (en) * 1978-08-19 1982-09-22 Foseco Int Blast furnace operation
RU2083681C1 (ru) * 1994-07-12 1997-07-10 Волгоградский государственный технический университет Брикет для производства чугуна и стали
DE19708376C1 (de) * 1997-03-01 1998-07-02 Gasteier & Bilke Verfahrenstec Verwendung eines Briketts aus Abfallmaterialien als Zuschlagstoff für Schmelzöfen einer Eisengießerei

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO02064846A1 *

Also Published As

Publication number Publication date
ZA200305964B (en) 2004-07-08
GB0103278D0 (en) 2001-03-28
WO2002064846A1 (fr) 2002-08-22

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