AbstractAs a leading mineral processing organisationMinelco supply a variety of raw materials tothe refractory industry. The purpose of thistwo-part technical paper is to review thesourcing, properties and applications of themajor refractory raw materials, some of which

are supplied by Minelco. In Part 1(IRE JournalMay 2011) the focus was on alumina basedproducts, in Part 2 we will concentrate onbasic (magnesia) raw materials.

IntroductionThere are several parameters that may

determine the type of raw material to use in abasic refractory product. Figure 1 lists a few ofthe possible service requirements that adesigner may need to consider. This means arange of basic raw materials need to be madeavailable to refractory organisations.

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An Overview ofRefractory RawMaterials – Part 2Basic Melvyn Bradley, Technical Manager, Minelco Ltd. Dr Tony Hutton, Assistant Technical Manager, Minelco Ltd

Hydration ResistanceCorrosion ResistanceThermal Shock ResistanceSlag ResistanceHot Load StrengthThermal ConductivitySlag CompatibilityVolume Stability

FIGURE 1

Basic Refractories are used in regions of heatresistant linings where the slags oratmospheres are basic and would thereforechemically attack alumina based refractories.Magnesia, Dolomite, Olivine and Chrome-Magnesia are commonly used basic Refractoryraw materials.

MagnesiteThe term magnesite should really refer to thenaturally occurring magnesium carbonatemineral however in refractory terms it is usedto refer to the high temperature productmagnesia (periclase). There are three generalgrades of magnesite produced from naturalmagnesite or magnesium hydroxide obtainedfrom sea water or from brine deposits.

i) Dead Burnt Magnesite (DBM) – isproduced by sintering/firing naturalmagnesite, MgCO3, at temperatures between1450 and 1760°C in shaft or rotary kilns,figure 2. Based on the conditions used and thequality of the raw materials this can producematerials with MgO contents between ~ 85 –98%. Although China is the largest producer ofDBM there are significant resources in NorthKorea, Turkey, Austria, Slovakia, Brazil, Russia,Spain and Australia. For refractory application,as well as MgO, lime, silica and iron contentare critical.

ii) Seawater / Brine Magnesite - is producedby adding limestone or calcined dolomite to

sea water/brine and precipitating outMagnesium Hydroxide, figure 3. The precipitateis formed into filter cake and can then eitherbe fired at temperatures >1800°C to form themagnesite or alternative the Mg(OH)2 is putthrough a low temperature decomposition at~1000°C to form MgO. This is then cooled andpelletised before it is sintered in shaft/rotarykilns. The Magnesia produced through thisprocess can also have varying MgO contentsbetween ~90 – 98% MgO; however, if a high

purity magnesia source is used in this processthen the products can have MgO contents inexcess of 99%. There are several syntheticmagnesia production plants around the worldincluding Japan, Netherlands, Ireland, USA,Mexico and South Korea. As with DBM carefulcontrol of lime, silica and iron content is

crucial to ensure good refractory properties.

iii)Fused Magnesite - is formed by meltingsintered magnesia in an electric arc furnace,figure 4. The resulting product is cooled andground into aggregate and powders. Generallyfused magnesite is manufactured in thelocations where natural magnesite is inabundance e.g. China, Turkey, and Australia etc

The three types of magnesite described above

are used in a variety of refractory applications.DBM is mostly used in the manufacture of basicmonolithics such as gunning repair products,tundish working linings and precast shapes(tundish dams/weirs). Applications forsintered magnesite include magnesia bricks,magnesia-carbon bricks, isostatic pressedshapes and flow control systems (sliding gateplates etc). These refractory products are usedin a number of areas in the steelmakingprocess including converter, EAF, ladles andcontinuous casting. Magnesia bricks are alsoused in cement kiln linings, the addition ofsmall amounts of alumina to produce amagnesia-spinel brick can help to improvethermal shock resistance in rotary cement kilnapplications. Fused magnesite tends to have

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FIGURE 2

DB Magnesite

Mined ore is calcined between Manufacturing Process 1450 – 1760°C, then crushed

and ground to required sizes.

MgO Content 85 - 98%

Other Chemistry SiO2, CaO, Fe2O3

Sea water/Brine Magnesite

Limestone or dolomite is added to sea water to precipitate out Magnesium

hydroxide.Manufacturing Process The hydroxide filter cake and can be…

- Fired directly into MgO or - Put through decomposition (~1000°C),

pelletising and sintering process (1800 - 2300°C).

MgO Content Regular 90- 98%, High purity >99%

Other Chemistry SiO2, CaO, Fe2O3

FIGURE 3

Fused Magnesite

Manufacturing Process Sintered Magnesite is melted in an Electric Arc Furnace, cooled and mechanically processed

to the required sizes.

MgO Content 95 – 99.9%

Other Chemistry More hydration resistant that DB Magnesite andSeawater Magnesite.

Thermal Behaviour Thermal and corrosion resistance, high thermal conductivity,

high bulk and apparent density.

FIGURE 4

superior properties to sintered magnesite andas such is incorporated into refractory productsused in high wear areas such as slag lines etc.

DolomiteDolomite is a calcium magnesium carbonatemineral, CaMg (CO3)2 which is locatedthroughout the world. The natural raw materialcannot be used in refractories and must becalcined (dead burnt) at high temperatures,figure 5. This is done with the addition ofsome iron or silica to assist in stabilising/semi stabilising the dolomite by removing

CaO as calcium ferrite or calcium silicate. Synthetic Dolomite clinker can also be

produced by the high temperature reaction ofcalcium hydroxide and magnesium hydroxidewith a small amount of an iron compound. Thechemistry of this synthetic material can beadjusted and the material offers improvedcorrosion resistance compared to the calcinednatural dolomite due to the lower levels ofimpurities present in the material.Dolomite is used predominantly in theproduction of refractory bricks. Unfortunatelydolomite bricks have one major disadvantageover mag-carbon bricks i.e. a tendency to“perish” when stored for a short period of timedue to reaction of free lime with moisture inthe air. Dolomite based refractories are mainly

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Dolomite

Manufacturing Process Natural Dolomite Calcined at ~ 1700°C / Stabilised Dolomite produced by reacting

CaOH and Mg (OH)2 at ~1760°C.

MgO Content >40% Typical

Other Chemistry Uncalcined raw material: MgO 18 – 22%, CaO 28 – 35%

FIGURE 5

Olivine

Manufacturing Process Mined ore is crushed to required sizes

MgO Content 48 – 51%

Other Chemistry SiO2 41 – 43%, Fe2O3 7 – 8%

Thermal Behaviour Low thermal expansion, Low thermal conductivity

FIGURE 6

The strength of the company, lies in its commitment to the needs of the market in general and to its customers in particular be it in terms of new product development, technical advice or urgent delivery requirements.

For 40 years the company and its employees have built an excellent reputation within the industry and the ‘AREL’ brand name for its products being synonymous with :-

QUALITY, RELIABILITY & SERVICE

For further informationPlease contact us at the followingP.O. Box 24, Dudley, West Midlands DY1 2RL

Tel: 01902 880123 Fax: 01902 880019E-mail: admin@robertlickley.co.ukwww.robertlickley.co.uk

UK MANUFACTURERS OF HIGH QUALITY MONOLITHIC & PRECAST PRODUCTS

used in stainless steel production where theuse of high lime slags are necessary to produceclean steel with low sulphur content.Refractory dolomite is also used in EAF fettlingproducts and specialist monolithics.

OlivineOlivine is a naturally occurring raw materialfound in volcanic rocks and although Olivine isfound in many areas of the world there are onlya few deposits that are commercially viable.Key deposits are located in Norway, Austria,USA, Turkey, Italy, Japan and China. Although Olivine is the name given to a seriesof materials with varying Mg/Fe ratios betweenthe end members, Forsterite (Mg2SiO4) andFayalite (Fe2SiO4) commercially the nameOlivine is used to designate a material thatconsists 85% or more Forsterite, 45-50% MgO,39-42% SiO2, 5-8% Fe2O3 and LOI < 2%, whilethe term dunite designates a rock thatcontains only 36-45% MgO and 36-39% SiO2and LOI ~10%, figure 6. Unlike most mineralsused in the refractory industry olivine does notrequire any thermal treatment to make itsuitable for use in most refractory applicationsand unlike other magnesia refractories it ishydration resistant. Finally although Olivine isa silicate material it does not contain any freecrystalline Silica.

Another unique characteristic of olivine is its

low thermal conductivity which makes it anideal component for tundish working linings.Olivine is also used as an EBT taphole filler, inMgO based gunning products and specialisedprecast shapes.

Magnesia-ChromeFor improved corrosion resistance Magnesia-chrome material is often used. This is formed

in an electric arc furnace from chrome ore andmagnesia aggregates, the melted material issolidified and the mechanically processed intothe grades required, figure 7.

Magnesia-chrome refractories are used inlimited applications such as RH Degassers,burning zone of rotary cement kilns and non-ferrous smelting (e.g. copper).

ConclusionMagnesia based materials are used in a widevariety of refractory products which can beused in a number of different applications.Therefore, it is important that several types ofmagnesia containing minerals are available torefractory organisations.

Acknowledgements:Refractories Handbook, The TechnicalAssociation of Refractories, Japan, June 1998Practical Refractories, Dr J D Hancock, 1988 A Review of the World’s current and potentialmagnesite resources – Ian WilsonMagnesia Availability Wallmap – Gerry M Clarke

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Magnesia-Chrome

Manufacturing Process Chrome ore and Magnesia aggregate are melted in an Electric Arc Furnace, cooled

and mechanically processed to the required sizes.

MgO Content ~67%

Other Chemistry Corrosion resistance to basic slags and molten iron/steel

FIGURE 7