Scientists of Ural Federal University and the Institute of Metallurgy of the Ural Branch of RAS (Russian Academy of Sciences) have developed and successfully tested the technology of joint non-waste processing of electric furnace and ladle slag to obtain pig iron and Portland cement clinker.

A paper on their work is published in the journal Steel in Transition.

Slag—a waste byproduct of steel production—from electric arc furnaces (EAF) and ladle (LF) slag is not completely utilized, the researchers said. Although residues of these slags are stored in dumps, these residues can be converted into valuable industrial products by interaction between the slag components.

The process of developing and testing the technology consisted of several stages. Ladle slag is most often presented as a dust fraction unsuitable for use in recycling processes. Therefore, first of all, experimenters stabilized the ladle slag in a solid state. For this purpose, borate glass, a cheap waste material that also requires processing, was added to it.

Obtaining clinker from ladle slag is a more complicated technological task than obtaining pig iron from electric furnace slag. For this reason, the researchers first calculated the conditions—the chemical composition of the mixture to be processed (charge) and the temperature range—required to produce clinker.

Then they used crushing and mixing to produce a charge with mixtures of the silica- and alumina-containing minerals alite, belite, celite and brownmillerite. Under laboratory conditions, the briquetted charge was heated in a furnace to 1500-1600 °C—i.e. to complete melting—held and then slowly cooled. The series of experiments showed that the quality of clinker corresponding to the state standard, is formed from five compositions of slag at a 10-minute curing at a temperature of 1540-1560 °C.

At the next stage, they selected similar in structure samples of waste electric furnace production at Seversky Tube Plant. Such samples are characterized by higher iron content. As a result of several laboratory melts using coke as a carbon reducing agent of iron simultaneously with Portland cement clinker, pig iron was obtained that also meets the requirements of state standards. At the same time all the starting materials were processed into marketable products.

The technology of joint non-waste production of pig iron and Portland cement clinker was successfully tested at the pilot plant of Klyuchevskoy Ferroalloy Plant. During the test melts the developers came to the conclusion that in order to avoid overheating and to control temperatures and economy it is necessary to use cheaper rotary inclined furnace instead of an arc furnace—a cylindrical tank slightly inclined horizontally and slowly rotating along its axis.

The charge, which is fed into the rotary tilting furnace through mixing, reduction and melting, produces pig iron and the slag residue, clinker. Subsequent mixing of the clinker with gypsum dihydrate and firing of the mixture in the kiln results in Portland cement, the most widely used type of cement.

Our technology allows the complete utilization of selected types of slag and thus solves the problem of anthropogenic load on the environment. It is especially important that we managed to achieve complete recycling of out-of-furnace slags: since there is very little iron in them, such slags are usually sent to landfills, constantly increasing the damage to the environment. —Oleg Sheshukov, lead author

Background. In ferrous metallurgy up to 85% of the total volume of solid wastes are slags from electric steelmaking and steel ladle treatment (final finishing of metal in the ladle for the purpose of homogenization by chemical composition and temperature).

Slag dumps occupy the areas exceeding 2.2 thousand hectares. Being located within the city limits, they pollute the environment. For example, ladle slag, most often presented in the form of a toxic dusty, fine-grained powder, is easily dispersed over large areas, then dissolved in sedimentary and groundwater.

At the same time, ferrous metallurgy slags, mostly electric furnace slags, contain up to 10% metallic and about 30% oxide iron, in addition to magnesium, aluminum, silicon, phosphorus, calcium, and lime. Recycling of slags and their reuse in production in the form of quality raw materials will help to solve the problem of depletion of mineral resources.

Sheshukov, O.Y., Egiazar’yan, D.K. & Lobanov, D.A. (2021) “Wasteless Joint Processing of Ladle Furnace and Electric Arc Furnace Slags.” Steel Transl. 51, 156–162 doi: 10.3103/S0967091221030116

Posted on 16 August 2021 in Manufacturing, Materials, Recycling | Permalink | Comments (0)

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