GB2437796A

GB2437796A - Improved blast furnace slag

Info

Publication number: GB2437796A
Application number: GB0608890A
Authority: GB
Inventors: John William Carson
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-05-05
Filing date: 2006-05-05
Publication date: 2007-11-07
Anticipated expiration: 2026-05-05
Also published as: GB0608890D0; GB2437796B

Abstract

An improved blast furnace slag made by the incorporation of raw materials with higher than conventional magnesia content, preferably with added fluxing and nucleating oxides, so as to produce a molten slag from which can be cast and annealed items of a glass ceramic nature. Preferably, the composition of the blast furnace slag is: SiO2 (30-80%); MgO (10-45%); CaO (10-30%); Al2O3 (5-30%). The fluxing oxides may be Li, Na, K, B or Pb (0.5 - 10%) and the nucleating oxides may be Al, Ba, Sn, Ti, V, Cr, Mn, Fe, Zn or Zr (0.5 - 10%).

Description

IMPROVED BLAST FURNACE SLAG

The present invention relates to a process for improving slags arising from blast furnace operation during the manufacture of iron, and for the production of glass ceramic cast items from this improved slag.

This process for the manufacture of improved blast furnace slag is based on making novel alterations to the conventional slag producing components of the blast furnace charge. The fuel and iron sources within the blast furnace charge remain unchanged. Only the components of the charge which give rise to the slag are changed in the present invention. Moreover the changes to the blast furnace slag composition do not adversely effect the operation of the furnace, the fuel consumption or the quality of the iron produced.

The principle alteration to the composition of the blast furnace slag is the increase in magnesium content and the decrease in calcium content. Additionally small percentages of fluxes and nucleating elements are added.

The present invention provide a novel process for the manufacture of shaped items by casting the resulting modified blest furnace slag. The production of castable items, from blast furnace slag, is made possible by the improvement in the high temperature characteristics of the blast furnace slag, brought about by the modifications to the chemical formula of the slag. 2.

This improved blast furnace slag remains fluid longer than conventional slag and so can be control poured and cast into moulds prior to the onset of setting. Once cast the cooling slag may be maintained at an annealing temperature so as to induce controlled micro crystallisation of ceramic entities within the otherwise glassy phase. Upon complete cooling the cast shape is a glass ceramic.

Glass ceramics have a range of structural properties which are superior to either glasses or ceramics and as such the cast shaped articles made via the above process have commercial significance.

Conventionally, blast furnace slag is made during iron production from calcarious limestone and silica containing sands, further constituents of the slag being derived from the impurities of the charge for example the iron ore. Because blast furnace slag has traditionally been regarded as an inexpensive co-product it has been used as the repository for the wastes involved in iron manufacture. Few significant attempts have been made to beneficiate this co-product in terms of its chemical analysis.

Significant work has, however, been conducted on modifying and improving the physical form of chilled blast furnace slag. Out of this work has come a range of physical forms produced by various chilling operations. Both chilling by air and by water have been extensively developed.

These techniques have resulted in grades of blast furnace slag suitable for usage as glass, ceramics and special cement raw materials, and aggregates for use in road construction and concrete manufacture. 3.

Currently blast furnace slag co-products are available in a wide variety of size ranges stemming from sub micron powders through dust grades, sand grades and gravels and up to aggregate grades with particulate diameters exceeding 100mm. This range of grades is, or can be made, available in either dry or moist forms.

The typical chemical analysis range of such conventional blast furnace slag co-products may be exemplified in terms of percentage composition by weight ranges, as follows: CeO; 30% to 50% Si 02; 30% to 50% Al203; 5% to 20% MgG 2%to 10% Additionally conventional blast furnace slag contains small percentage quantities of manganese, iron and titanium, as oxides.

Attempts have previously been made, notably in the British Iron and Steel Industry between 1940 and 1965, to cast shaped articles from conventional blast furnace slags. This venture was known in the industry as the SIag-ceram project. The aim of this venture was to produce ceramic products of the roofing tile type.

Because of the conventional chemical analysis of blast furnace slag it proved difficult to produce such ceramic cast items. This difficulty stems from the rate of cooling, viscosity increase and hardening of conventional molten blast furnace slag. In the terrninolgy of the industry, blast furnace slag is a short glass, which means it remains liquidous and shapeable for only a short time period as it cools. 4.

Various development options were tried, in the Slag-ceram project, in atiempts to obviate this difficulty. These included insulating the molten slag to increase its thermal retention. However these approaches proved ineffective.

Because the targeted end products of the Sleg-ceram project were inherently low value1 no economically viable process modification was found, and the venture to produced shaped cast items from molten blast furnace slag was abandoned.

Since the time of the Slag-ceram project many techno-economic business parameters involved in various sectors of manufacturing industry have changed significantly. These changes have had a major impact on the possibility of the economic production of cast shaped items from molten blast furnace slag. These developments are reviewed in the following paragraphs.

The most significant relevant change in business parameters has been the rapid increase in fuel costs. This has been so marked as to cause major reappraisals of energy consumption throughout manufacturing industry. Wherever fuel or energy or waste heat could be conserved this has become an industrial priority. Viewed against these changed parameters the low co-product value recovered from the high thermal energy values involved in molten blast furnace slag is now commercially and environmentally unacceptable.

Glass. ceramic and glass ceramic technology have advanced greedy over the past four decades. There is now a recognition that the physical properties of the intermediate category of substances called glass ceramics warrants re-evaluation. 5.

The technology now exists to enable the production of glass ceramics with exceptional resistance to; abrasion, impact, thermal shock, electrical conductivity and various corrosive and solvating chemicals.

Commercially, new market niches have evolved that will generate needs for the large scale manufacture of ranges of cast shaped glass ceramic items of considerable economic value.

Examples of such glass ceramic items include; monolithic exterior construction panelling, single skin building brick bolts and industrial impact and abrasion resisting chute cladding tiles.

However, the production of any and all of these new products from the thermally rich molten blast furnace slag depends on finding ways of beneficiating the slag.

I have carried out extensive research into the physico-chemical composition known as glass ceramics. Developmental data discovered of relevance to the present patent is presented in the following paragraphs: Glass ceramics derive their exceptional properties, such as resistance to abrasion, impact.

chemical and heat from their physico.-chemical structure. This physico-chemical structure involves microscopic crystals dispersed through a glass phase. Glass ceramics may be regarded as composite materials because the crystallites are dissimilar in chemical composition to the glassy phase. They may also be regarded a reinforced structures because the crystallites tend to be dendritic and radiate in interlocking arrays from nucleation sites. 6.

The chemical composition of both the crystallites and the glassy phase has a direct relationship on the physico-chemical properties of a glass ceramic, in several specific ways.

Firstly the chemical composition of the molten form dictates the extent to which they can be further processed in a fluidic form. Secondly, this melt composition dictates the suitability of the cooling casting to be annealed. By annealing in this context we mean being held at an elevated temperature but below the melting point to induce ceramisation. Ceramisation is the terni used to define the generation via nucleation of the ceramic crystallites within the glassy phase. Thirdly the original chemical formula of the melt ultimately dictates the chemical formula of both the crystallites and the residual glassy matrix. Fourthly this chemistry in turn has a significant bearing on the physico-chemical properties of the cast item.

Much research has been carried out on determining the optimum chemistry of melts from which different types of glass ceramics can be cast. From my work in this field has emerged ranges of formulations for the manufacture of various glass ceramics from various raw materials.

Specifically, my research has led to the novel compositions of matter, derived from conventional blast furnace slag, which are the subject of this present invention.

From my research into glass ceramics it has now been discovered according to the present invention that a chemical modification to blast furnace slag can be made which enables the manufacture of cast shaped items of a glass ceramic nature which have commercial significance. The specific research which has led to this discovery will be outlined in the following paragraphs. 7.

Conventional blast furnace slag is, chemically, an inappropriate substance from which to make structurally sound glass ceramics. Its analysis shows that it is too rich in calcium to produce a melt which is long in terms of fluidic properties. Additionally, even if a simple shaped item is cast and annealed the resulting product is of an inferior glass ceramic nature. This inferiority also stems from the high levels of calcium, which produces relatively soft crystallites. which are high in calcium and low in other essential elements such as magnesium.

It is now known that the addition of magnesium to high calcium melts can provide a route to glass ceramics with exceptional physico-chemical properties. This stems from the fact that the additional magnesium induces the formation of a very hard crystallite based on a magnesium alumino silicates, known as cordierite. Cordierite, as defined herein, has the following analysis: Mg2Al2Si5Ola It has further been discovered that various trace metals elements may beneficially be added to the melt to increase the rate and completeness of the formation of cordierite crystallites throughout the glassy matrix.

Additionally it has been discovered that certain simple fluxing oxides may also be added to the melt to extend the fluidity during cooling, that is the longness of the molten stage of the glass ceramic.

The addition of magnesium at the expense of calcium, plus the addition of nucleating and fluxing oxides, has now been shown to convert conventional blast furnace slag into an improved substance, from which shaped glass ceramic items can be successfully cast. 8.

Taken together the above improvements have now been shown to be effective in a process for the improvement of the value of blast furnace slag. Specifically its thermal value when molten can now be maximised via the manufacture of economically significant shaped castings in highly durable glass ceramics.

This recognition, that the principle addition of magnesium to conventional blast furnace slag would allow for the manufacture of economically significant glass ceramic items, is the basis of the present invention. The specific way in which blest furnace slag is to be improved will now be described: Essentially what is proposed is a modification to the raw materials used in the blast furnace process for iron production. This modification concerns only the calcarious based raw material additions currently made. The aim of the proposed modification would be to significantly increase the magnesium content of the resulting slag at the expense of the calcium content.

There are several ways in which this proposed modification can be achieved. These all have in common the addition of substances containing significant levels of magnesium oxide, that is magnesia. These substances may provide either magnesia directly or as the result of the calcination to which the substance is subjected during blast furnacing. Examples of such magnesia providing substances are the minerals; dolomite, olivine and magnesite and the synthetic see-water magnesia. It should be noted that this list of substances are only examples. Any magnesium containing substance, which may be safely added to a blast furnace, can be used according to the present invention. 9.

The chosen substance, intended to provide significantly increased levels of magnesia in the slag, is to be substituted proportionally for the calcareous limestone contentionally used. The extent of this substitution will depend on the desired level of magnesia in the beneficiated slag.

This can be calculated knowing the magnesia level of the limestone and other ingredients conventionally used and the magnesia content of the chosen substituting substance.

The invention described herein provides for the addition of magnesia bearing substances to blast furnaces, as part or complete replacement of the calcareous limestone conventionally used, so as to significantly increase the magnesia content of the slag at the expense of the calcium oxide ie calcia content.

In addition to the essential addition of substances which introduce significant additional levels of magnesia to the slag, there are additional less significant but still beneficial additions that may be made to the blast furnace slag. These further additions will now be described.

The first type of further additions are fluxes, that is substances that flux molten glassy melts.

By fluxing, in this context, we mean substances that either reduce the melting point of the glass or reduce the viscosity of the molten glass at any specific temperature. The fluxing of glasses in this way is well understood in the industry. Typical of such fluxes that can be used in conjunction with the beneficiation of blast furnace slags according to the present invention are substances which yield lithium, sodium, potassium, boron, lead, phosphorous. Selected examples of substances that yield one or more of the above elements may be added to provide additional levels of 0.5% to I 0% in the slag. A typical example is the addition of oxidic salts of boron, such as a sodium borate added so as to provide 3% by weight of the oxides in the slag. 10.

The second type of further additions are nucleating agents, that is substances that nucleate the formation of crystallites within the cooling molten slag. The nucleation of glasses in this way is well understood in the industry. Typical of such nucleating agents are oxides of metals such as aluminium, barium or tin and oxides of transition metals such as titanium, vanadium, chromium, manganese, iron, zinc or zirconium. A typical example is the addition of an ore such as rutile so as to provide 3% by weight of titania in the slag. It may be noted that several of the above listed substances can be present in conventional blast furnace slag, in which case the addition may not be necessary.

It should be noted that the chosen fluxes and/or nucleating agents may, depending on their type, be added either to the blast furnace feed or to the molten blast furnace slag. It will also be noted that it is not possible to add significant quantities of iron oxides to the improved blast furnace slag via additions to the blast furnace feed, because the blast furnace process will convert such additions into metallic iron. However, this is not an impediment to the present invention because the desired glass ceramic is low in iron oxide content. Any small additions of iron, or other elements which cannot be added to blast furnace feed, can be added aspo furnace additions to the molten slag.

The present invention will now be described in general terms: The present invention is an improved blast furnace slag, which is differentiated from conventional blast furnace slags by the following numbered compositional features: 1. The improved blast furnace slag has significantly higher magnesia content than conventional. 11.

2. The improved blast furnace slag had a significantly higher flux content than conventional.

3. The improved blast furnace slag has a significantly higher nucleating agent content than conventional.

Thus, the composition of matter which is the basis of the present patent may be defined as a high magnesia, fluxed and nucleated improved blast furnace slag.

Chemically, this glass ceramic composition of matter may be defined, in general terms, as the following oxide formula by weight percentage: S102 30%toBO% MgO 1O%to4O% CaO 1O%toSO% A1203 5% to 30% Fluxing oxides 0.5% to I 0% Nucleating oxides 0.5% to I 0% The improved blast furnace slag described in the present invention may be composed of the following essential elements within the percentage by weight ranges defined: Si02 30% to 80% MgO I0%to4O% CaD I0%to3O% 41203 5% to 30% 12.

In addition to these essential or primary elements, the improved blast furnace slag may be made to include any or a combination of the following fluxing or secondary elements within the range 0.5% to I 0% by weight Uthium oxide Sodium oxide Potassium oxide Boron oxide Lead oxide Phosphorous oxide Additionally the improved blast furnace slag may be made to contain at least one of the following nucleating ingredients, within the range 0.5% to I 0% by weight.

Aluminium oxide Barium oxide Tin oxide Titanium oxide Vanadium oxide Chromium oxide Manganese oxide Iron oxide Zinc oxide Zirconium oxide 13.

The method by which the improvement to blast furnace slag may be made will now be described.

Essentially the improvements defined in the present invention, can be made to blast furnace slag by the substitution of quantities of substances normally added to blast furnace feeds with alternative high magnesia substances. The following examples may be used to eludicate the approach used to the manufacture of the proposed improved blast furnace slag:

Example I

This first example presents an approach that can be used to produce an improved blast furnace slag with a modest increase in magnesia content. It is based on the replacement of calcarious limestone with dotomitic limestone. The following substitution should be made on a parts by weight basis: From every 100 parts calcarious limestone; Replace 30 parts with dolomitic limestone; Add 1% mineral borax.

Add 1% mineral rutile.

The resulting improved blast furnace slag can be cast into simple shapes such as roof tiles.

Example 2

This second example presents an approach that can be used to produce an improved blast furnace slag with a medium increase in magnesia content It is based on the replacement of calcarious limestone with olivine. The following substitution should be made on a parts by weight basis: 14.

For every 100 parts of calcarious limestone; Replace 40 parts with mineral olivine.

Add 2% mineral borax.

Add 2% mineral rutile.

The resulting improved blast furnace slag can be cast into large surface ares building construction panels.

Example 3

This third example presents an approach that can be used to produce an improved blast furnace slag with a high increase in magnesia content. It is based on the replacement of calcarious limestone with magnesia. The following substitution should be made on a parts by weight basis: For every 100 parts of calcarious limestone; Replace 60 parts with mineral magnesite.

Add 3% mineral borax.

Add 3% mineral rutile.

The resulting improved blast furnace slag can be cast into complex three dimensionally shaped items such as brick bolts for single skin building construction.

The process by which improved blast furnace slag may be cast into glass ceramic items will now be described: 15.

The improved blast furnace slag arises from the blast furnace as a motten material. The methods by which this may be safely handled are well known in the industry. However, in addition to the conventional safe handling of slags care should be taken to insulate and accelerate the handling of the improved blast furnace slag intended for use in the production of glass ceramic items.

Essentially the molten slag should be cast as quickly as possible. This process involves the provision and preparation of appropriate moulds or moulding equipment which may have to be pre-heated.

Additionally, to facilitate post kiln additions and effective casting, some re-heating of the slag may be required. Again conventional systems are well known in the industry. It should be noted however that this thermal input, in the form of re-heating, is small in comparison in the thermal energy present in the molten slag as it exits from the blast furnace.

The actual casting of the molten slag utilises plant and processes which are well known in the industry. These may include casting a ribbon or sheet onto rollers; casting a ribbon or sheet onto molten tin as in the float-glass process; or casting the molten slag into moulds with or without cores as in various metal casting industries, or adding a bloating agent and casting in the form of a foamed sheet. 16.

Subsequent to casting it is normally necessary to anneal the cast items, which will be in the cooling molten state. This annealing process involves holding the items, where appropriate contained in their moulds, at a temperature below the melting point of the glassy phase of the glass ceramic but at a sufficiently high temperature and long dwell time to induce satisfactory ceramisation. In practice, for most examples of the glass ceramic products made from improved blast furnace slag 1050 C for 1 hour in sufficient. However, specific ceramisation routines have been developed for specific forms of cast glass ceramic, as part of the process covered by the present invention.

After annealing, the glass ceramic items so produced may be cooled normally to ambient temperature, however this cooling rate should not exceed 10 C per minute.

The physico-chemical nature of the range of glass ceramics which may be produced from improved blast furnace slag will now be described: Physically, the glass ceramic items that can be produced from improved blast furnace slag are durable solids, which is to say hard wearing. Typically they exhibit both abrasion and impact resistance. These characteristics are demonstrated by Mohs hardness of higher than 7 and modulus of rapture greater than I 600Kg/cm2.

Chemically, the glass ceramic items that can be produced from improved blast furnace slag are magnesium calcium alumina silicate glasses containing dendritic crystallites based on the mineral cordierite, ie magnesium alumina silicate. 17.

Analytically, the glass ceramic items that can be produced from improved blast furnace slag may be defined in terms of the following weight percentage oxidic analysis range: Si1 30%toBO% MgO 10%to4O% CeO 10%to3O% A1203 5% to 30% Fluxing oxides 0.5% to 10% Nucleating oxides 0. 5% to I 0% Examples of cast shaped items of a glass ceramic nature which may be manufactured from improved blast furnace slag according to the present invention, will now be exemplified.

Item I This first example of a glass ceramic product according to the present invention relates to a roofing or walling tile for use in building cladding. An improved blast furnace slag made to the formula defined earlier as Example I may be used to manufacture commercially advantageous roofing tiles and wall cladding shingles with larger than conventional surface area and thinner than conventional profile. Additionally, lugs, sockets, fixing points and other three dimensional feature may also be cast into this type of glass ceramic product. A still further advantage of such products is that they demonstrate 0% water adsorption and permeability and can have a relatively low density of 2.4 g/cc. 18.

Item 2 This second example of a glass ceramic product according to the present invention relates to an industrial abrasion resistant tile for use in chute lining. An improved blast furnace slag made to the formula defined earlier as Example 2 may be used to manufacture commercially advantageous chute lining tiles with greater than conventional cast basalt or ash based tile abrasion resistance, as indicated by Mohs hardness of between 8 and 9 as compared to high iron basalt or ash tiles which measures 7 to 8. A still further advantage of such products is that they can be cast thinner and in larger surface area tiles and in thin curved profiles and still weigh less than cast basalt This weight advantage has an economic impact in terms of the chute supportive structure.

Item 3 This third example of a glass ceramic product according to the present invention relates to a brick or block locating bolt for use in single skin building construction. An improved blast furnace slag made to the formula defined earlier as Example 3 may be used to manufacture advantageous glass ceramic bolts that fit into holes in either ceramic bricks or concrete blocks. When fitted such bolts so improve the structural stability of walls that a single skin construction will suffice in many applications. A still further advantage of such products is that they reduce or eliminate the need for mortar. 19.

Item 4 This fourth example of a glass ceramic product according to the present invention relates to an exterior cladding panel for use in fast.build construction. An improved blast furnace slag made to the formula defined earlier as Example 3 but additionally treated with a bloating agent may be used to manufacture lightweight thermally insulative external modular construction panels for fast build assembly. Typically such panels may measure 2.2m x I m x 10mm. In spite of their size and thinness such panels are structurally sound because of the extensive arrays of crystallites reinforcing their composite structure. Also, because of their low iron content such panels can be made semi transparent.

The overall advantage of the present invention will now be defined: Improved blast furnace slag is a thermally rich composition of matter with wide versatility in terms of formula and physico-chemical properties. As such it can be seen as an important new techno-commercial product which is both economic in manufacture and environmentally friendly.

The present invention allows for the conversion of this low value co-product into an advanced composite material with high commercial value.

The glass ceramic composition of matter produced via improved blast furnace slag has exceptional durability which enables its usage in a wide range of demanding applications. The glass ceramic produced, according to the present invention, is superior to all previous slag based compositions, and products made from either natural basalt or synthetic ashes. 20.

The glass ceramic items, which it is proposed to manufacture from improved blast furnace slag, will find a wide range of applications in such industries as construction, transportation and defence wherein the unique reinforced composite nature of glass ceramics are particularly valuable.

The reader's attention is directed to all papers and documents which are filled concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification [including any accompanying claims, abstract anddrawings) and/or all of the steps of any method or process so disclosed. may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive.

Each feature disclosed in this specification [including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the detail of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification [including any accompanying claims, abstract and drawings), or to any one or more novel combination of the steps of any method or process so disclosed. 2'I.

Claims

CLAIMS

1. An improved blast furnace slag wherein the magnesia content has been significantly increased in comparison to conventional blast furnace slag.

2. An improved blast furnace slag made by increasing the input to the blast furnace of ores or synthetic chemicals or wastes containing higher levels of magnesia than is conventional.

3. An improved, that is a high magnesium, blast furnace slag suitable for forming into glass ceramic items via a process of casting and annealing.

4. A composition according to claims I to 3 including the following oxides as essential ingredients: Si02 30%toBO% MgO IO%to45% CeO IO%to3O% Al203 5% to 3O% 5. A composition according to claim I to 4 including the following additional oxides: Fluxing oxides; Li. Na, K, B. Pb. 0.5% to I 0% Nucleating oxides: Al. Ba. Sn. Ti. Vs. Cr, Mn. Fe. Zn. Zr 0.5% to I 0% 6. A glass ceramic composition and an approach to its formulations and production substantially as described herein.