A modified ferro silicate SLAG suitable for shot blasting

Abstract

The present invention relates to a ferro silicate slag, which has been modified to be suitable for shot blasting. The slag consists of the following components SiO2 26 - 46 CaO 0.1 - 7 Al2O3 5 - 15 MgO 0.1 – 5 Na2O ≤ 1.8 ZnO ≤ 1.5 Cr203 ≤ 0.9 Fe2O3 ≤ 10 S ≤ 0.8 impurities ≤ 5 FeO* balance wherein FeO* is the total Fe calculated as Fe2+ and wherein the matrix of the modified ferro silicate slag comprises an amorphous continuous phase.

Description

[0001] A MODIFIED FERRO SILICATE SLAG SUITABLE FOR SHOT BLASTING

[0002] TECHNICAL FIELD

[0003] The present invention relates to a ferro silicate slag, which has been modified to be suitable for shot blasting.

[0004] BACKGROUND ART

[0005] Shot blasting materials are abrasive materials, which are used to remove rust, old coatings, oxidized layers and surface contaminants from a surface in order to prepare the surface for a new coating.

[0006] In the past, silica sand was often used for this purpose, but due to the inherent health hazards there has been a strive to use safer materials.

[0007] For this reason, different types of blasting materials based on metallurgical slags have been developed and patented in the past in GB914337A, JPS5959350A, JP2000290048A, JP2000290048A and US20080120917A. More recent developments are described in US2022332994A, US2023256566A and US20150101257 A. The object of the latter was to provide a shot blasting abrasive material, having a crushing strength in combination with a high Fe content. In particular, a crushing strength of 176 N (18 kgf) or more for particles having a size of 2.0 mm or more was strived for. For this reason it was found desirable that the abrasive material should have an amorphous continuous phase, preferably with crystalline phases dispersed therein.

[0008] Copper slag, a by-product from the copper smelting industry, is also widely used as a shot blasting material due to its high density, chemically inertness and a very low content of free silica, which is hazardous to the health. The copper slag is a ferro silicate slag but its composition varies with the type of ingoing materials and the type of processing. SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide an alternative ferro silicate slag suitable for shot blasting.

[0010] A particular aim is to provide a modified ferro silicate slag, having an amorphous continuous phase as well as having a high hardness and / or a high crushing strength. A further object is directed to optimize the slag composition to improve the productivity and / or reduce the consumption of the ferro silicate slag, when used in dry abrasive shot blasting. However, the inventive material can naturally be used for other purposes such as anti-slip screed, road surface dressing, construction material, grout, black colorant and / or as a filler or as a binder replacement for Portland cement in concrete and cement.

[0011] DETAILED DESCRIPTION

[0012] The inventors of the present invention have carried out an extensive research program and have found that it is under certain circumstances possible to provide a modified ferro silicate slag having an amorphous continuous phase as well as having a high hardness.

[0013] The chemical composition of the modified ferro silicate slag has to be controlled within the limits set out in the independent claim.

[0014] The importance of the separate constituents and their interaction with each other as well as the limitations of the ingredients of the claimed modified ferro silicate slag are briefly explained in the following. All percentages for the chemical composition of the SCM are given in weight % (wt. %) throughout the description. The amounts of the microstructural constituents are given in volume % (vol. %).

[0015] The broadest aspect of the invention is set out in claim 1. The inventive idea is valid for the whole scope of claim 1. Upper and lower limits for one or more of the chemical constituents may be freely combined within the limits set out in claim 1 in order to form a more limited range for the one or more elements. This may be necessary in order to delimit the invention over the prior art. Accordingly, multiple combinations are expressly allowable for all constituents defined in claim 1 and there is no need or pointer for a certain combination, because such a combination solely leads to a limitation of the scope of protection and not to a new invention. It is also allowable to form a new range for an element by the combination of two different values of an upper range or by the combination of two different values of a lower range.

[0016] The arithmetic precision of the numerical values can be increased by one or two digits for all values given in the present application. Hence, a value reported as e.g. 0.1 % can also be expressed as 0.10 or 0.100 %.

[0017] The starting material used for producing the modified ferro silicate slag may be based on a ferro silicate slag but it is also possible to mix different starting materials to obtain the desired composition. Iron-rich ferro silicate slags originate for instance from copper and lead production. The composition of these slags varies considerably depending on the starting materials, which may be ore or scrap. The inventive modified ferro silicate slag can be produced by modifying the composition of a copper slag to fall within the limits set out in the independent claim.

[0018] SiO2

[0019] SiCh is the main net-work former and is necessary for obtaining an amorphous matrix.

[0020] The lower limit is 26 % and may be set to 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40 %.

[0021] The upper limit is 46 % and may be set to 45, 44, 43 or 42 %.

[0022] FeO*

[0023] FeO* constitutes the balance in the modified ferro silicate slag, wherein the presence of Fe in all oxidation states is expressed as FeO*. The content of FeO* should preferably be balanced to the content of SiO2in order to obtain a desired ratio of FeO* / SiO2. A high amount of FeO* can be used to increase the density of the quenched slag. However, the amount of FeO* is generally in the range of 35 - 51 %. FeiOs

[0024] The amount of Fe2O3 should be low. The maximum content is 10 % and may be set to 9, 8, 7, 6, 5, 4, 3, 2 or 1 %. The reason for restricting the amount of Fe2O3 is related to the fact that Fe2C>3 may lead to an undesired crystallisation phases.

[0025] FeO* / SiO2

[0026] The ratio FeO* / SiO2 is 0.7 - 1.7 and should preferably be 0.76 - 1.37. A low ratio increases the propensity to form tridymite and cristobalite upon cooling. A high ratio increases the propensity to precipitate fayalite and / or spinel during cooling. Accordingly, the ratio can be used in order to obtain a desired amount of precipitates in the amorphous matrix.

[0027] The lower limit may be 0.8, 0.85, 0.9 or 0.95. The upper limit may be 1.35, 1.3, 1.25, 1.2, 1.15, 1.1 or 1.05.

[0028] CaO

[0029] The lower limit is 0.1 % and may be set to 0.5, 1, 1.5, 2, 2.5 or 3 %.

[0030] The upper limit is 7 % and may be set to 6.5, 6.0, 5.5, 5, 4.5, 4, 3.5 or 3 %.

[0031] AI2O3

[0032] The effect of AI2O3 is not fully understood but the results of an extensive experimental program performed by the applicant indicate that a fairly high content of AI2O3 could be beneficial for forming a matrix containing an amorphous continuous phase.

[0033] The lower limit is 5 % and may be set to 5.5, 6, 6.5, 7, 7.5 or 8 %.

[0034] The upper limit is 15 % and may be set to 14.5, 14, 13.5, 13, 12.5, 12, 11.5, 11, 10.5, 10, 9.5 or 9 %.

[0035] MgO

[0036] MgO may enter the slag from chrome-magnesite and other MgO containing refractories used. The lower limit is 0.1 % and may be set to 0.5, 1 or 1.5 %.

[0037] The upper limit is 4 % and may be set to 3.5, 3, 2.5 or 2 %.

[0038] ZnO

[0039] The upper limit is 1.5 % and may be set to 1.4, 1.3, 1.2, 1.1, 1.0, 0.95, 0.9, 0.85 or 0.8 %. Na2O

[0040] Na2O is a flux that heavily reduces the viscosity of the molten slag as well as the melting temperature and is therefore an undesired component in the present invention.

[0041] The upper limit is 1.8 % and may be set to 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.95, 0.9, 0.85 or 0.8 %. The lower limit may be set to 0.1, 0.2, 0.3 or 0.4 %.

[0042] Cr2O3

[0043] Cr2O3may enter the slag from chrome-magnesite refractories or from the charging material. Cr2C>3 can also be deliberately incorporated in the slag in order to facilitate the precipitation of crystalline phases such as spinels.

[0044] Impurities

[0045] The modified ferro silicate slag may contain conventional residual elements or impurities, which are not intentionally added but originate from the raw materials, the refractories or from the atmosphere during the processing. The term impurities include all type of impurities such as metals, non-metals, oxides and sulphides. Accordingly, a non-limiting list of impurities embraces: MnO, K2O, Cr2C>3, Cu2O, Sb2O3, Pb2O3, TiO2, P2Os, SO3, S and Cu as well as the elements As, Bi, Cd, Hg, Ni, Mo, V, Zr, Ba, Sr and / or the compounds thereof.

[0046] The upper limit is 5 % and may be set to 4.5, 4.0, 3.5, 3, 2.5, 2, 1.5 or 1 %. However, for environmental reasons and / or for improving the Cu recovery, it may be beneficial to restrict the upper limit of S to 0.8 %. The upper limit of S may be set to 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 %. The upper limit of K2O may be restricted to 1 % and may be set to 0.9, 0.8, 0.7, 0.6, 0.5, 0.4 or 0.3 %.

[0047] The matrix of the modified ferro silicate slag comprises an amorphous continuous phase, which may comprise up to 30 volume % crystalline phases. The amounts of crystalline phases can be restricted to 25, 20, 15, 10, 5 or 2 vol. %. The matrix may be fully amorphous but a lower limit of 1, 2, 3, 4, or 5 vol. % crystalline phases is also conceivable.

[0048] The hardness of the modified ferro silicate slag can be influenced by the chemical composition and the amounts of crystalline phases. The Mohs hardness is preferably at least 6 and may be as high as 6.5 or 7. The express as HV0.2 is at least 610 and may be set to at least 615, 620 or 625. The density of the modified ferro silicate slag is preferably 3400 - 4200 kg / m3. The lower limit may be set to 3450, 3500, 3550, 3600, 3650 or 3700 kg / m3.

[0049] EXAMPLE 1

[0050] A modified ferro silicate slag was prepared by melting reagent grade chemicals of Fe, Fe2O3, SiCE, AI2O3 and MgO in an iron crucible in a graphite resistance heated furnace held under inert atmosphere. The slag was heated to 1236 °C and held at this temperature for 2 hours. The crucible was removed from the furnace and subjected to water granulation with cold tap water at a flow rate of 1.1 L / s.

[0051] The granulated slag was dried and analysed using inductively coupled plasma mass spectrometry. The modified ferro silicate slag had the following composition in wt. %:

[0052] SiO236

[0053] FeO* 54

[0054] CaO 1

[0055] AI2O3 8

[0056] MgO 1

[0057] FeO* / SiO21.5

[0058] The granulated slag was examined for crystalline phases by X-ray spectrometry using calcite as internal standard. The slag was found to be fully amorphous.

[0059] EXAMPLE 2

[0060] A second modified ferro silicate slag was prepared and granulated in the same way as for example 1, but the holding temperature was 1244 °C.

[0061] The dried granulated slag had the following composition in wt. %:

[0062] SiO227

[0063] FeO* 64

[0064] CaO 1

[0065] AI2O3 7 MgO 1

[0066] FeO* / SiO22.4

[0067] The granulated slag was examined for crystalline phases by X-ray spectrometry using calcite as internal standard. The slag was found to be 90.1 weight % amorphous and contained 3.3 weight % spinel and 6.6 weight % fayalite. The reason for the formation of crystalline phases is believed to be that the composition of the slag is close to the stochiometric composition of fayalite.

[0068] EXAMPLE 3

[0069] The effect of content of AI2O3 was examined in this example. The modified ferro silicate slag was prepared by melting reagent grade chemicals of Fe, Fe2O3, SiO2, ALCh and MgO in an iron crucible in a graphite resistance heated furnace held under inert atmosphere. The slag was heated to 1238 °C and held at this temperature for 2 hours. The crucible was removed from the furnace and subjected to water granulation with cold tap water at a flow rate of 1.1 1 / s.

[0070] The granulated slag was dried and analysed using inductively coupled plasma mass spectrometry

[0071] SiO233

[0072] FeO* 52

[0073] CaO 1

[0074] A12O313

[0075] MgO 1

[0076] FeO* / SiO21.6

[0077] The materials were examined by XRD and the material was found to be fully amorphous and the free silica content was less than 0.1 %.

[0078] EXAMPLE 4

[0079] The material was prepared by melting and water granulation in the same way as for example

[0080] 3. The slag was heated to 1234 °C and held at this temperature for 2 hours. The crucible was removed from the furnace and subjected to water granulation with cold tap water at a flow rate of 1.1 1 / s.

[0081] SiO241 FeO* 49

[0082] CaO 1

[0083] AI2O3 8

[0084] MgO 1

[0085] FeO* / SiO21.2

[0086] The material was examined by XRD and the material was found to have an amorphous content of 98.5 vol. %,

[0087] INDUSTRIAL APPLICABILITY

[0088] The modified ferro silicate slag of the present invention is suitable for dry abrasive blasting.

Claims

CLAIMS1. A modified ferro silicate slag for shot blasting, wherein the slag consists of the following componentsSiO226 - 46CaO 0.1 - 7 ALOs 5 - 15 MgO 0.1 - 5Na2O < 1.8 ZnO < 1.5 Cr203 < 0.9Fe2O3 < 10S < 0.8 impurities < 5 FeO* balance wherein FeO* is the total Fe calculated as Fe2+, and wherein the matrix of the modified ferro silicate slag comprises an amorphous continuous phase.

2. The modified ferro silicate slag defined in claim 1, wherein the amorphous continuous phase comprises up to 30 volume % crystalline phases.

3. The modified ferro silicate slag defined in claim 1 or 2, wherein the slag fulfils one or more of the following requirements,SiO236 - 43CaO 1 - 4AI2O3 5.5 - 14MgO 0.1 - 4Na2O < 1.5K20 < 1.0ZnO < 1.0Cr203 <0.6Fe2C>3 < 10S <0.7 impurities <4 FeO* 35 - 51 and / or wherein the ratio FeO* / SiO2in the slag is 0.8 - 1.2, and / or wherein the amorphous continuous phase comprises 1-20 volume % crystalline phases.

4. The modified ferro silicate slag defined in any of the preceding claims, wherein the slag fulfils one or more of the following requirements,SiO239-43CaO 1-4A12C>3 6-14MgO 0.1 -4Na2O 0.1 - 1.0K2O <0.5ZnO 0.05-0.9Cr203 0.05-0.5Fe2O3 < 5S <0.6 impurities <3 FeO* 43 - 505. The modified ferro silicate slag defined in any of the preceding claims, wherein the slag fulfils one or more of the following requirements,CaOAI2O3MgONa2OK2OZnO 0.05-0.8Cr203 0.05-0.4Fe2C>3 < 5S <0.5 impurities <26. The modified ferro silicate slag defined in any of the preceding claims, wherein the slag fulfils one or more of the following propertiesMohs hardness >6HV0.2 >610 density (kg / m3) 3400 - 42007. Use of the modified ferro silicate slag defined in any of claims 1 to 5 as anti-slip screed, road surface dressing, construction material, grout, black colorant as a filler in concrete or as a binder replacement for Portland cement.

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