FR2477574A1 - Processing solid slag for use in glass industry - by magnetic sepn., crushing and screening - Google Patents

Abstract

The slag is manually sorted on a conveyor to remove impurities which are visible to the naked eye, automatically magnetically sorted to remove coarse magnetisable particles, passed through a cascade of crushers, and screened to remove coarse particles, which are more rich in iron silicates, in order to obtain a slag having a Fe2O3 content of max. 0.5% and a magnetic iron content lower than 0.06%. The resulting slag, after further purificn., has the compsn. 20-50% SiO2, 5-25% Al2O3, 5-50% CaO, 15% max. MgO, 0.5-2% MnO, traces of colouring components (expressed as Cr2O3 and NiO) 0.5% max. Fe2O3, 2.0% max. Na2O, 2.0% max. K2O and 3.0% max. S(2-), with a tolerance of 0.5% for S(2-), 1.0% for MnO-Na2O-K2O and 2.0% for SiO2-Al2O3-CaO-MgO. Process is useful for treating slags, such as blast furnace slags, which have been cooled slowly or rapidly in air or water, to make it useful in the glass industry. The slag reduces the risk of gas occlusion in the glass, has a low m.pt. so that it improves the rate of glass melting, contains lime so that the glass is less fragile, contains alumina so that devitrification risks are reduced and contains magnesia so that the plasticity range of the glass is increased.

Description

 The present invention relates to a process for treating steelmaking slag, both cooled slowly and suddenly in a stream of air or water in order to make them suitable for use in the glass industry.

 The steel slag is a material which already has an important range of uses (road industry, cement industry, glass industry, ceramics, etc ...) which it seems possible to widen by proposing new industrial applications .

 The use of blast furnace slag as a raw material for the production of glass has been common for the past twenty years.

 The slags used were first used as a cheap source of CaO and AL203, but their use was strictly limited to the production of dark glasses, because of the coloring elements which they contained (Fe - Mn - S).

 The steel slag consists of a mixture of silicates which can, by rapid cooling, form glasses. However, the resistance of the silica network is not, in the majority of cases, sufficient to ensure good stability; it is therefore advisable, during the manufacture of the glass, to add silica. On the other hand, certain compounds naturally present in raw slag can interfere because of their coloring, devitrifying or difficult to fuse character, which is the case in particular with iron oxides. It is therefore important to sort, classify and process the slag.

There are four types of slag - cooled in atmospheric air, density = 1.12 to 1.36 - expanded, process identical to casting
with water glass ovens, density = 0.4 to 0.7 - granulated, density = 0.96
pouring takes place in a stream of water
or in a basin full of water - pelletized, the slag is cooled in a stream of steam
of water on a rotating drum.

Air cooling is used more and more the product is then crushed.

 Untreated slag can be either slag crystallized in an open or closed pit, or slag granulated in a stream of water or on a rotary drum.

 In the case of a slag granulated in a stream of water for example, the product is in the form of a wet sand with friable and porous grains of gray color with light ocher containing impurities which will be eliminated later and whose chemical composition can reach the values of the example in Table I.

 By way of example, the particle size of the granulated slag may have the distribution of table II.

To be usable in glassware, the content of
Fe203 should be as low as possible especially if you want to use the slag in a white glass. This low Fe203 content is obtained by an electro-magnetic iron removal treatment. In addition, the slag must not contain any magnetic particles, because they dissolve badly in the glass and corrode the refractories.

 The content of AL203 must be as high as possible (the slag is a cheap source of alumina) but also as constant as possible because too great variations in the content of AL203 would cause chemical heterogeneities (strings) in the objects.

 The S content must be high and constant.

A variation in the content of sulphides contained in the slag causes a modification of the degree of oxidation-reduction of the bath and risks degrading the refining of the glass.

 For some glasses, the MnO content should be as low as possible.

 Slag milked from a raw slag of the above type may correspond to the characteristics of Table III.

 In general, in accordance with the present invention, the treated slag will have a composition defined by the limits of Table IV.

 The pro cOdF of homogenization and primary treatment will be described in more detail below.

 In the case of slag cooled slowly in an open or closed pit, it is first conveyed by a belt conveyor to the crushing plant and undergoes on this conveyor a first manual sorting allowing elimination of the impurities visible to the 'naked eye (refractory debris for example) then automatic sorting by electromagnetic system to remove the largest magnetizable particles.

 The material is then passed through a cascade of conventional crushers (percussion type for example) then sorted on a screen to remove the largest particles which, due to their resistance to crushing, prove that they contain the elements richer in ferrous silicate. A judicious choice of the adjustment of the crushers and the screening size makes it possible to eliminate a granular fraction d / D mm unfit for the desired use and to keep only a fraction O / d suitable for further processing for its use. in a batch.

 As a general rule, it has been found that the optimal screening dimension d mm is of the order of 4 to 6 mm.

 The homolgénéPsation of the product is carried out by the constitution of stock of equal chemical composition after verification of the latter, the mixture being produced during the recovery for further treatment.

 In secondary treatment, the slag (granulated in a stream of water or on a rotary drum, cooled slowly in an open or closed pit and pretreated in the form of 0/4 or 0/6 mm sand) is taken up from the stocks of homogenization and can be the subject of a pneumatic sorting adapted to the granulometry, making it possible to eliminate on the screen the densest elements therefore the most concentrated in ferrous oxides and silicates which will be directed towards another use than that envisaged in glassmaking , but it is not an obligation to provide this pneumatic treatment, especially during the treatment of granulated slag.

TABLE I Element SiO2 Al2O3 CaO MgO MnO Fe2O3 Na2O K2O S-- magnetic particles
Rate 33.7 15.6 41.2 5.4 0.8 1.5 0.7 0.8 0.9 0.6
TABLE II
Sieve 0.063 0.08 0.100 0.160 0.200 0.250 0.315 0.5 1.0 2.0 2.5 3.15 5.0 in mm
Tamisat 0.4 1.2 2.0 3.0 4.0 6.5 8.5 20.5 52.5 90 96.5 99 100 in%
TABLE III
Chemical composition :
Element SiO2 Al2O3 TiO2 Fe2O3 MnO CaO MgO Na2O K2O S-- magnetic particles
Rate 32.5 15.3 0.7 0.3 0.7 43.2 5.1 0.5 0.7 1.0 0.05%
Particle size analysis ::
Sieve 0.08 0.100 0.160 0.200 0.250 0.315 0.500 1.00 1.25 in mm
Rate 9 14 21 26 31 39 63 97 100 in%
TABLE IV
CaO SiO2 Al2O3 MgO Fe2O3 MnO, S-40 to 45% 30 to 35% 15 to 17% 4 to 6% # 0.5% 0.5 to 0.8% 0.8 to 1.2%
Subsequently, the slag is dried in a suitable installation (rotary dryer for example), taking care to limit the temperature of the material at the outlet of the dryer to around 70/120 C in order to avoid unfavorable phenomena (modification grain size, release of sulfur dioxide).

 Following the drying operation, the material is introduced under a magnetic field used to remove iron oxides unrelated to the material, these are removed separately.

 The demagnetization operation is followed by thorough grinding in a bar mill, which makes it possible to bring the product to the particle size specified by the user.

 The ground product is directed to a single-stage screen which, in addition to scaling the material to the desired size, also eliminates certain elements harmful to the use in glassware such as ferrous silicate and metal beads (from makes them more resistant to grinding).

 After the screening operation, the product undergoes demagnetization on a permanent field magnetic drum, the bed of material being perfectly regulated as a function of the treatment flow rate thanks to a dosing system with flaps and electromagnetic vibrators.

 Following these various operations, the product is suitable for direct delivery to the glass factory or for the manufacture of a vitrifiable mixture by adding silica sand and other adjuvants.

 It has been proven that the treated slag can be used to make all soda-lime type glasses and that only the quantity of treated slag can vary according to the type of glass (dark glasses - semi-white glasses - white glasses).

 The alkali and alkaline earth metal sulfates have always been used as refining agents. Their action results from their thermal decomposition which takes place in the presence of molten glass between 1300 and 14000 C. This decomposition causes an energetic stirring of the glass bath and creates very numerous bubbles which drain the bubbles of other occluded gases towards the surface of the bath. in the molten glass. Unfortunately, this thermal decomposition of the sulfate occurs almost at the end of the glass making process and may not be complete when the oven draw becomes large. The solubility limit of the gases in the glass being very low, we will find these gases in the form of gaseous inclusions (defects called chips and broths) in finished objects.

On the other hand, the sulfates are chemically decomposed from 900 C, when using slag from blast furnaces. This decomposition results from the chemical reaction between the sulphate and the sulphides of calcium, sodium, iron and manganese which are contained in the slag.
3 S04 Na2 + CaS (dairy) # 3 Na20 + CaO + 4S02
This reaction occurring at low temperature, therefore earlier in the glass making process, the chances of finding gases in the final glass resulting from a late decomposition of sulfates will be significantly reduced.

The improvement in the melting speed of the batch is directly linked to the fact that the slag is an excellent flux since it is a silicate with a low melting point.

To obtain appreciable improvements
melting and refining speeds of a glass, the quantity of sulphides (expressed in S) must be equal to or greater than 0.35 kg per tonne of molten glass (which corresponds to approximately 35 kg of slag per ton of glass). The effectiveness of sulfides increases with the quantity introduced, but from an amount of the order of 0.5 kg, the gains become very small.

 According to the above equation, the 803/8 ratio is 7.5 but in fact in current practice, it turns out that an excess of sulfate should always be used. As a general rule, it is accepted that this excess must be at least 50%, so the ratio S03 / S - must be greater than 11.

 Each furnace will have optimum levels of slag and sulphate additions according to the tonnage drawn, the type of furnace, the type of composition put in, the combustion atmosphere ... It is only after systematic tests that these quantities are determined.

 The quantity of slag introduced into the glass is moreover limited by - the AL2O3 content of the glass - the Fe2O3 content of the glass (case of white glasses which contain very little Pue203) - the presence of other dyes (MnO for example) - the quality of the slag used.

The main advantages of introducing slag into glass doughs are as follows: 1) reduced risk of finding gas trapped in
end of refining in the oven, due to decomposition
tion of sulfates at 9000 instead of 13000C.

2) the treated slag being a low fu silicate
sion (1200 to 1500 C), it has the characteristics
excellent fondant and therefore improves ~
substantially the melting speed of the vitrified mixture
able 3) The lime present in the treated slag allows reduction
ser the fragility of the glass 4) the alumina existing in the treated slag increases the
fusibility of the glass paste and reduces the risks
glass devitrification 5) the magnesia of the treated slag increases the interval
plasticity of glass.

These main advantages are reflected in the following improvements in the production of glass 1) increased output from the furnaces which, in the opti
ma, can go up to 10 to 15% 2) decrease in specific calorie consumption by
kg of glass which can vary from 3 to 8% depending on the load
of the furnace 3) improvement of the quality of the glass 4) improvement of the refining phase of the glass in particular
when the oven output is not increased 5) increase in the life of the ovens due to the dimi
senible change in glass-making temperatures.

The use of blast furnace slag is a good example of valorization of a by-product. Originally used in glassware, as a raw material providing
A1203 and CaO, it can now be used as a smelting and refining accelerator. The generalization of its use is possible thanks to the improvement of its quality by specific treatments.

Claims (7)

 1) Process for treating steel slag cooled slowly or suddenly in a stream of air or water in order to make it suitable for use in the glass industry, in which the slag is blown on a conveyor a first manual sorting making it possible to eliminate the impurities visible to the naked eye, then an automatic sorting by electromagnetic system making it possible to eliminate the largest magnetizable particles, the material then being passed through a cascade of crushers, such as of the percussion type for example, then sorted on a screen in order to eliminate the coarsest particles which, because of their resistance to crushing, prove that they contain the elements richest in ferrous silicates so as to finally obtain a slag having a lower Fie 203 content or equal to 0.5% and a magnetic iron content of less than 0.06%.  2) Process according to claim 1, in which the slag is then taken up on the homogenization stocks and is subjected to a pneumatic sorting adapted to the particle size, making it possible to eliminate on the screen the densest elements therefore the most concentrated in ferrous oxides and silicates, then the slag is dried in a suitable installation such as a rotary dryer so that the temperature of the material o the outlet is between 7Q and 120 C.  3) Method according to claim 2, wherein the material is then introduced under a magnetic field used to remove iron oxides not bound to the material.  4) Method according to one of claims 2 or 3, wherein the material is further subjected to a final grinding in a bar mill.  5) Steel slag for glass use, obtained with the method according to one of claims 1 to 4, characterized by a chemical composition within the following limits  SiO2 20 to 50%  AL2O3 5 to 25%  CaO 5 to 50%  MgO <15%  MnO 0.5 to 2%  Coloring elements (expressed as Cr203-NiO) tra  these  Fe2O3 # 0.5%  Na2O <2.0%  K2O # 2.0%  S # 3.0% with tolerances allowed for each component of # 0.5% for S- # 1.0% for MnO - Na2O - K2O + 2.0% for SiO2 - AL203 - CaO - MgO  6) Dairy according to claim 5, characterized in that the content of some of the elements is within the following limits  SiO2 30 to 35%  AL2O3 15 to 17%  CaO 40 to 45%  MgO 4 to 6%  MnO 0.5 to 0.8%  S 0.8 to 1.2%  7) Any vitrifiable mixture containing less than 30% of steel slag obtained according to one of claims 1 to 4.