LU83669A1 - PROCESS FOR THE RECOVERY OF A METALLURGICAL SLAG - Google Patents

Description

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Claim of the priority of the corresponding request (£) filed in -— on ___ 0¾. AO. 1¾ 80_i__ under n ° 8 8 5 ^ X / _ [U C 2077/8010.

Λ - ‘» METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association - Vereniging zonder winstoogmerk in BRUXELLES, (Belgium)

Process for the recovery of a metallurgical slag.

The present invention relates to a process for the recovery of metallurgical slag, and especially metallurgical slag obtained during the refining of hematite cast iron "pneumatically in a converter.

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The slag, metallurgical produced by the refining of a non-phosphorous cast iron according to the process in which one blows industrially pure oxygen in the converter, finds, currently, only limited outlets. .

These outlets are essentially, either agriculture, where because of its high CaO content, this slag is used in small quantities to amend the earth, or the intrcw duction in the load of blast furnaces, as flux and f jf 2 .-. .

v carrier of iron, but in limited quantities, due to the presence of annoying impurities (phosphorus, alkalis) contained in these slag. These slags are also used for road construction, but difficulties arise when the lime content of these slags is too high (swelling). The large surplus of unused slag is generally dumped, a solution which has, among other disadvantages, that of requiring expenditure in pure loss, since the material is considered to be irrecoverable.

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In order to recover these slag, the applicant has already recommended adding carriers to the liquid slag! alumina and silica (fly ash from thermal power stations, possibly blast furnace slag, preferably liquid). These additions have the effect of transforming the liquid slag into a metallurgical binder. A reducing agent is added sufficiently energetic to reduce most of the FeO and MnO to the metallic state and during this reduction, oxygen is injected into the gaseous atmosphere released from the slag.

The present invention also aims to enhance the aforementioned metallurgical slag, but for another purpose, namely to prepare by means of these slags an advantageously ground product which can be used as powder for continuous casting or enter with interest. in the composition of cover powder for continuous casting mold. Such a powder is automatically of the pre-ground type.

The process which is the subject of the present invention is essentially characterized in that metallurgical slag produced during a pneumatic refining operation of cast iron in a converter is mixed in preferably liquid form with: _a. fly ash from coal-fired power plants, possibly shale from coal, silico-aluminous products or waste, blast furnace slag pre / fiercely liquid, individually or in mixture. (not a word

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3.- b. pure silica or weakly aluminous sand, that is to say, verifying the relation A ^ 2 ° 3 y 0.17 # the proportions in-

Sl02 be the two constituents listed under a. and B. being such that the total content eQ silica is less than 70% and preferably more than 30%, more preferably more than 40%, in that the mixture thus formed is first of all subjected to a heating operation advantageously by means an appropriate burner, so as to maintain the mixture in the liquid state, then a reduction operation under an electric arc with the addition of carbon-bearing elements, the mixture being after reduction, preferably cooled by pouring into a liquid such as water, while the metal by-products can be collected by decantation, for example in the form of ferro-manganitic cast iron, etc.

According to the invention, the heating operation can be carried out with the addition of 1 fluxes, such as for example fluorspar, alkalis, Li ^ O, alone or in a mixture, which has the effect of on the one hand, to accelerate the fusion and on the other hand, to provide a product directly usable in continuous casting. The reducing elements carrying carbon can be solid, liquid or gaseous, pulverulent, individually or as a mixture. These fluxes can also be added at the end of the reduction operation. Optionally, the two modes of addition can be used. · „After solidification of the reduced, cooled mixture, it is finely ground and having an advantageous component for the intended use, can be used without .other manipulation as a covering powder for a continuous casting mold.

It has also been found also advantageous / to mix said powder before use, with compounds / sensitive to pyrolysis, with gaseous evolution, such as // y CaCO ^ or carbonaceous such as graphite.

4.- v The example below will help you better understand the process for preparing the above-mentioned powder.

We have an LD slag comprising:

41/6% CaO

15.3% Si02

5.3% MgO

21% total Fe, in oxidized form, almost entirely, the balance being made up of various components.

On the ternary diagram Αΐ ^, Ο ^ “^ ° 2“ tCa0 + such a slag contains: - in (CaO + MgO): -Qrß + 5'3- = 75.4% 41.6 + 15.3 + 5 , 3 - in SiO_: _ 15.3_ _ 24.6% * 41.6. + .15.3 + -5.3 • It "is represented by point 1 (called ideal LD) on the said ternary diagram. One tonne of this slag therefore contains 469 kg of (CaO + MgO) and 153 kg of Si02>

We also have fly ash comprising:. . 47% Si02.

32% of AlnOn.

2 3.

3% CaO, the balance being made up of various components.

Related to the ternary diagram. Α120 ^ - Si02 "(CaO + MgO), the contents of these three constituents are respectively: 57.4,% of Si02 39% · of Al203. \ \ 3.6% of CaO.

Such ashes are thus represented on the diagram by point 2. (called ideal fly ash).

On the other hand, it is known experimentally that a good quality cover powder should not normally exceed an alumina content of 10%. In the present example, the Ca0 / Si02 ratio is of the order of 0.8? for good- / ne quality powders, this ratio can vary in relative proportions v 5.-

wide ·. Given that the addition of sand will help to decrease the alumina content of the primary mixture # we can estimate that the alumina content of this primary mixture (LD slag

+ fly ash) or around 12 ’% / which allows to - finish point A on. line 1 - 2, representative of the mixture ”· to be produced.

The quantities of ^^^ ales ^ ideal ^ implement to achieve this mixture spnt determined in a known manner · by the rule of the segments measured on the diagram. · ·

In the present case, we will therefore have:.

r * \ 7. .

ideal _ l.A _ 23, 5_n or 43, 9 LD. -x. 7C2 "5373" '100 ideal therefore 43.9 kg of ^ j ^ ales For ^ 00 ^ g of ^ ideal' This corresponds to 43, 9 = 53.6 kg of CV, ,, and JL9.Q— kg of v Ô7 & Z real 0.622 '“real = 161 k9 ·

If we now consider adding silica (pure SiC> 2). with the primary mixture represented by point A, one seeks to obtain a final mixture containing 10% of alumina, which, on the right connecting point A to point 3 (corresponding to 100%

Si02), brings us to point 4..

1. '·. ·; The relative proportions of the primary mixture and of silica are given by the segment rule, namely: Aidéal mixture _ 475 = 58 = 420 ·

Si02 ÄT4 3.'3 ”8 100 ·

It follows that, taking the data from the beginning, we will have for 1 ton of real LD slag 1000 '. 53.6. 0.82 = 273 kg • 161.

ideal fly ash, which corresponds to 895 kg of ideal mixture A, to be mixed with 895 x 100 _ 213 kg of silica. , 420 · /

The materials introduced to constitute the actual mixture / final represented in A will therefore be: f1 / * t * 273 6.-

1000 kg of LD slag

333 kg of fly ash = qq 213 kg of silica, or 1545 kg out of which 309 kg of metallic products (cast iron-ferro-manganese, etc.) must be counted off during the • formation of the molten mixture, which gives ultimately 1236 kg of actual mixture obtained.

This mixture, after quenching with water, is minus ground. 50 jU, and add CaC0.3 and graphite in the following proportions: 62.8 kg of ground mixture 28 kg of CaCO ^ 9.2 kg of graphite, the latter two components also being crushed within 50 days *. , all corresponding to 100 kg of cover powder, which can be used directly as such.

It is worth noting that thanks to the fly ash, the. powder naturally contains 0.16% Na2O and 0.5% F ^ O. An additional quantity of alkalis and possibly CaF2, Li ^ O B2 ° 3 Little <: ®tre added to the molten phase or after cooling (in the latter case, after grinding corresponding to less than 50 p.), To finally obtain a final content of 1.6% in ^ £ 0; 0.3% in F ^ O and 3.6% in F, to which responds a covering powder considered of quality for the continuous casting of steel.

-. The present process can be applied regardless of the type of converter used for the production of slag, that is to say also, both solid-bottom converters and / or bottom-blown converters. / 1/7

Claims (5)

7 .- V f 1. A process for the recovery of a metal-lurgical slag, characterized in that metallurgical slag produced <in a pneumatic refining operation of cast iron in a converter is mixed in liquid form with: . fly ash from coal-fired power plants, possibly shale from coal, silico-aluminous products or waste, blast furnace slag, preferably liquid, alone or in mixture, b. 'of pure silica or weakly aluminous sand, that is to say verifying the relation ^ -2 ^ 3 z 0.17> the proportions between- Si02 ^ be the two constituents listed under a., and b. being such that the total silica content is less than 70% and preferably more than 30%, more preferably more than 40%, in that the mixture thus formed is firstly subjected to a heating operation advantageously by means of an appropriate burner, so as to maintain the mixture in the liquid state, then to a reduction operation under electric arc with the addition of carrier elements. carbon, the mixture being after reduction, preferably cooled by pouring into a liquid such as water, while the metal by-products can be collected by decantation, for example in the form of ferro-manganitic iron, etc. . 2. Method according to claim 1, characterized in that the heating operation is carried out with the addition of / fluxes, such as for example fluorspar, alkalis, dw / I ^ O, & 2 ° 3 'is ° single or mixed. (il / •! m v; 8.- ‘ 3. Method according to claims 1 or 2, ca characterized in that during and preferably at the end of the reduction operation, fluxes are added, such as, for example, fluorspar, alkalis, "Li20, B2 ^ 3 '^ -so ^ meI1 ^ or mixed. 4. Method according to one or other of the claims 1 to 3, characterized in that after cooling, the said mixture is ground into a powder, preferably less than 50 µm. 5. Method according to either of claims 1 to 4, characterized in that the said powder is mixed before use, with compounds sensitive to pyrolysis. with gaseous evolution such as CaCO ^ or carbonaceous, such as graphite. Drawings: - plates, ____ & .______ pages of which ....... S ...... cover page ....... é> ..... description pages ....... ....... claim pages: ..... descriptive abstract Luxembourg, le -2 OCT, 1981; - Charles München. ''