The metallurgical industry is one of the largest sources of wastes. Some of them, however, owing to their content of metals such as zinc or iron, may become valuable secondary raw materials. In order to achieve that purpose, they require appropriate preparation. This article provides a discussion on the methods of preparation of scrap from steelworks, namely deposits containing iron oxides, enabling their recycling

K. Nowacki

P. Musiał

T. Lis

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Methods of preparing deposits containing iron oxides for recycling

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263METALURGIJA 52 (2013) 2, 263-266T. LIS, P. MUSIAŁ, K. NOWACKIMETHODS OF PREPARING DEPOSITS CONTAINING IRON OXIDES FOR RECYCLINGReceived – Prispjelo: 2012-06-04Accepted – Prihvaćeno: 2012-10-15Review paper– Pregledni rad ISSN 0543-5846METABK 52(2) 263-266 (2013)UDC – UDK 669.1:549.5.004.08=111T. Lis, P. Musiał, K. Nowacki - Silesian University of Technology, De-partment of Metallurgy, Katowice, PolandThe metallurgical industry is one of the largest sources of wastes. Some of them, however, owing to their content of metals such as zinc or ir on, may become valuable secondary raw materials. In order to achieve that purpose, they require appropriate preparation. This ar ticle provides a discussion on the methods of pr eparation of scrap fr om steelworks, namely deposits containing iron oxides, enabling their recycling.Key words: iron-bearing deposits, recycling, deoilingINTRODUCTIONThe domestic metal processing and metallurgical in-dustries have seen quite considerable restructuring processes and transformations within the recent few years, those resulting mainly from the IPPC (Integrated Pollution Prevention and Control) Directive implemen-tation. The IPPC Directive imposes the necessity of procuring what is referred to as an integrated permit for operation in the European Union upon the installations whose environmental impact is particularly strenuous. The purpose of an integrated approach towards environ-mental protection is such application of BATs (Best Available Techniques) that enables the negative envi-ronmental impact of those installations to be minimised. Application of such solutions have caused the quantities of waste materials retained in deposits of industrial fa-cilities to increase. One of the characteristic properties of those materials is a considerable content of compo-nents that may be utilised under numerous technologies, being comparable to the content of the same compo-nents in natural resources.The possibilities of using wastes as raw materials while applying different technologies decrease the quantities being stored. Waste materials, prior to their utilisation, require speciﬁ c preparation. This paper pro-vides a presentation of various methods enabling appro-priate preparation of waste materials in the form of oily deposits (sludges) containing iron oxides for recycling.METALLURGICAL WASTESDeposits (sludges) produced while iron and steel are manufactured and processed can be divided into the fol-lowing groups [1,2]:–  pure iron-bearing deposits of the iron content ex-ceeding 60 wt % including deposits from scraper troughs of sintering plants, deposits (sludge) from wet ﬂ ue gas treatment at converter plants, deposits from cleaning of cooling installations for metal-lurgical machinery,–  contaminated iron-bearing deposits containing 15 - 40 wt% of iron – the most common contaminants are alkalis, zinc, oil; they also include deposits (sludge) from blast furnace gas treatment, deposits from neutralisation of chemicals used in certain steel manufacturing technologies,–  oily scale of the iron content exceeding 60 wt% mainly formed in continuous steel casting and rolling installations; their oiling degree may ex-ceed 10 % on the water content of 25 – 30 %,–  deposits formed while working of metal compo-nents, e.g. grinding residues containing 10 - 15 % of coolant.Depending on the chemical composition of deposits as well as their contamination and water content, the options of their utilisation as a secondary raw material and recycling preparation technologies may vary.PREPARING DEPOSITS FOR RECYCLINGPreparing deposits for recycling, regardless of their chemical and phase compositions as well as the subse-quent application, may be brought down to the follow-ing basic technological operations [2]:–  drying, i.e. moisture reduction in deposits through mechanical or thermal processing,–  mixing which enables homogenisation and correc-tion of chemical composition and moisture con-tent,–  optional operations of contamination reducing, e.g. deoiling,–  granulation or briquetting to reduce the volume and provide the wastes being processed with ad-264  METALURGIJA 52 (2013) 2, 263-266T. LIS et al.: METHODS OF PREPARING DEPOSITS CONTAINING IRON OXIDES FOR RECYCLINGvantageous features enabling their transport, stor-age or recycling.The choice of methods for preparing deposits for re-cycling also depends on the type of machinery to be used to utilise the waste material. Regardless of the sub-sequent recycling manner, the preliminary operations of deposit preparation must be aimed at reduction of the water content and homogenisation of the mixture [2] composed of deposits only or containing both deposits and other waste materials such as dusts. One of the most economically sound ways to remove water from depos-its is mixing them with dry waste materials like dusts and ashes. Hence the drying and mixing operations are often conducted alternately. The operations performed to remove the excess of water from deposits are thick-ening, ﬁ ltering and drying.Sludge thickening (thickening of dust particles une-venly scattered in water) is usually conducted in settling tanks where gravitational sedimentation and bottom deposition of solid particles take place. The most com-mon thickening plant is the Dorr settling tank enabling the thickening degree of 50 - 75% to be obtained [3]. The water which accumulates on the settling tank’s sur-face contains no more than 0.1-0.2 g/dm3 of contami-nants and may be used to supply the given facility with process water. The slurry obtained as a result of sedi-mentation may also contain ca. 25 - 50% of water. Com-plete separation of deposit lumps can be obtained on the moisture content of ca. 20 wt% of H2O, whereas on the moisture content of 10 - 15 wt % of H2O, the deposits become loose [2] which facilitates their batching in fur-ther technological operations. In order to remove the excess of water, the deposits are subject to ﬁ ltration by means of negative pressure drum-type ﬁ lters or plate-and-frame ﬁ lter presses [2]. The moisture content of a ﬁ ltered product comes to 8 – 13 %. The ﬁ nal stage of deposit dewatering is drying. The drying machines used on an industrial scale include [2]: rotary drum driers, multi-band driers, ﬂ uidised-bed driers and vacuum dri-ers (based on application of reduced pressure). The lat-ter may prove particularly useful in drying of waste ma-terials contaminated with environmentally hazardous substances. The efﬁ ciency of the drying process mainly depends on the surface area of the substance being dried, the manner in which heat is supplied and uniform distribution of the heat ﬂ ux on the drying surface. An example of the vacuum-based drying technology is the Evactherm device manufactured by Eirich [4]. It con-tains a vacuum chamber, where a high-intensity agitator is installed, to which superheated steam is delivered. As a result of intense stirring of dried wastes and simulta-neous impact of a high-energy medium that the super-heated steam is, heat is exchanged across the entire vol-ume of the material being dried. The water steam re-leased is removed from the vacuum chamber via circuits of forced gas circulation, condensation and condensate distillationSome of basic operations in the waste material recy-cling technologies are mixing and homogenisation aimed at obtaining such a mixture of the said materials that would have uniform grain and chemical composi-tion across the entire mixture volume. The devices that meet the contemporary industrial requirements are quick-rotating centrifugal mixers, also known as intense mixers [4 - 6]. Homogenisation is particularly impor-tant when small amounts of additives, for instance bonding agents, are used. According to the latest tech-nological solutions, intense mixers are installed inside vacuum chambers.Lumping operations. Industrial lumping methods in-clude sintering of ﬁ ne-grained materials, pelletising of powdered materials and briquetting. Briquetting can be applied to materials of inhomogeneous grain composi-tion. Sintering is a thermal process as a result of which an agglomerate of speciﬁ c resistance is obtained through partial melting of the surface of the grains being sin-tered. This agglomeration method is particularly useful in iron ore enrichment. Lumping is a method of forming lumps from ﬁ ne and powdered materials of the grain size not exceeding 0.1 mm. It is recommended that in-tense mixers should be used for this operation, since granulation in an intense mixer occurs across the entire volume of the material being processed, it does not re-quire as complex control as in a plate or drum mixer and it provides the surface of granules with advantageous features inﬂ uencing their rheological properties as well as prevents the typical granulate defects such as empty centre from occurring [4, 5, 7]. In the process of ﬁ ne-grained and powdered material lumping through bri-quetting, in the ﬁ rst stage, the materials are subject to pressing under a speciﬁ c pressure followed by the sec-ond stage of the briquette hardening. In the technology of material briquetting, besides the strength factors, an-other important parameter is the ability to absorb water which is referred to as moisture absorption [8]. It is par-ticularly crucial when the product subject to briquetting is assumed to be stored or transported under diverse weather conditions.UTILISATION OF OILY DEPOSITS CONTAINING IRONOily deposits are currently utilised in small quanti-ties, exactly like the EAF dusts [9,10], in production of Portland cement clinker or as a colouring additive in concrete production. Wider application of those waste materials is difﬁ cult because of their oiling. The oil con-tent precludes their direct utilisation in sintering plants equipped with electrostatic precipitators due to the haz-ard of self-ignition and heat ﬁ res.Methods applied for deoiling of deposits containing iron extend the options of utilisation of the iron-bearing metallurgical wastes deposited in dump sites by recy-cling them into the steel manufacturing process or using them in non-metallurgical industries.Two environment friendly solutions for deoiling of iron-bearing deposits have been described below.265METALURGIJA 52 (2013) 2, 263-266T. LIS et al.: METHODS OF PREPARING DEPOSITS CONTAINING IRON OXIDES FOR RECYCLINGThe ﬁ rst one, being a system for utilisation of oily metallurgical wastes, has been depicted in Figure 1 [11]. It consists of a reactor (1) equipped with a feeding screw (2) and nozzles (3) installed along the entire length of the feeder. The nozzles are used to pulverise the deoil-ing and/or degreasing solution delivered to them via tubes (4) from a mixer (5). In the lower section of the reactor (1), there is a feeding mechanism (6) for the oily deposits containing iron, whereas in the upper section, one will ﬁ nd the outlet of the deoiled waste, usually having the form of scale. Oily deposits are deoiled by spraying with a 3-15% solution of organic acid or deter-gent in the reactor at the temperature of 330-350 K for 20-45 minutes depending on the waste material size grade and oiling degree. The reactor is connected with an overﬂ ow-type efﬂ uent settling tank (8) and a treat-ment plant (7) owing to which the system does not exert a negative environmental impact. There is also a possi-bility that the deoiling and/or degreasing agent should be recycled to the process. The deoiled scale may be subject to granulation in a plate or briquetting prior to its further utilisation.degrading of petroleum derivatives. The deoiling prod-ucts are: hydrocarbon vapours, steam and deoiled met-allurgical waste (scale). The deoiled scale is delivered to the cooling chamber, whereas the degrading process vapours to the condenser. After the deoiling process, the deoiled metallurgical waste becomes an iron-bearing raw material containing iron oxides. There is, however, a certain problem on the way, since the deoiled scale is very broken-up. The deoiled scale may be subsequently subjected to granulation or briquetting. The installation delivered by Eko-Fortuna Sp. z o.o. exerts no negative impact on the natural environment. It is used to deoil both iron-bearing discards from rolling as well as de-posited waste. The chemical composition of such de-posits received from a single facility has been provided in Table 1 – they represent averaged deposits from two bore-holes of the depth up to 5 m. The moisture content Figure 1 System for utilisation of oily metallurgical wastes [11]The second solution is an installation for metallurgi-cal waste deoiling provided by Eko-Fortuna Sp. z o.o. (Figure 2) [12] which consists of the following units:– deposit batching point,– heating chamber with a pallet conveyor,– cooler for pure deoiled metallurgical wastes,– pure metallurgical waste storage point,–  condensing point for fumes from the heating cham-ber (steam and oil vapour condenser, separator).The oily metallurgical waste is subject to prelimi-nary drying in a storage reservoir after which it is deliv-ered to the batching tank with a water jacket where fur-ther heating takes place. Heated batch (metallurgical waste) is supplied with a belt conveyor to the heating chamber equipped with a pallet conveyor where the metallurgical waste is deoiled. The waste material de-oiling occurs under the impact of the temperature inside the heating chamber which comes to ca. 670 K, fol-lowed by evaporation of the remaining moisture and Table 1  Chemical composition of the deposits obtained / wt%Chemical composi-tionBore-hole I Bore-hole IIFe2O3 86,1 81,6FeO 4,62 2,61CaO 3,26 4,76SiO2 2,01 2,34Al2O3 0,20 0,43MgO 0,79 1,52MnO 0,78 0,82Cr2O3 0,03 0,03K2O 0,08 0,10Na2O 0,06 0,05P 0,04 0,04S 0,10 0,11Zn 2,02 1,52Pb 0,36 0,37C 1,09 2,01Figure 2  Deposit deoiling installation by Eko-Fortuna; 1 - dosing tank, 2 - conveyor, 3 – heating chamber, 4 – water condenser, 5 – oil condenser, 6 – cooler, 7 – storage centre [12]266  METALURGIJA 52 (2013) 2, 263-266T. LIS et al.: METHODS OF PREPARING DEPOSITS CONTAINING IRON OXIDES FOR RECYCLINGof the deposits came to 28 - 36 % whereas their proper density was 4,56 - 4,86 g/cm3.The deoiled iron-bearing deposits obtained from the aforementioned installation contain from 58,7 % to 63, 8 % of Fe. After the deoiling, they can be used for man-ufacturing of blast furnace sinter as the iron ore replace-ment. The iron content in the deoiled deposits is only slightly lower than in imported iron ores which, for in-stance for Canadian red iron ore, comes to 67 % Fe.CONCLUSIONSProtection of natural resources should become the superior goal of mankind. One of the ways to achieve this goal is recycling of the wastes produced and depos-ited. Developing further methods and technologies ena-bling utilisation of materials currently being classiﬁ ed as wastes is, therefore, highly reasonable. Installations used to prepare wastes for recycling, including oily de-posits containing iron oxides, must not exert negative impact on the natural environment, and this is the case for the installations described in this paper.The products of deoiling of iron-bearing deposits us-ing the installation provided by Eko-Fortuna are water steam, hydrocarbon vapours and scale having the iron content of ca. 60 %. The scale obtained, assumed to be used in the sintering process, may well replace the ore, and not only does it reduce the current production costs but also contributes to preservation of natural resources. The steam after condensation is used to heat the depos-its introduced to the installation, and after its complete cooling it may be utilised as process water, whereas the condensed hydrocarbon vapours are a high-quality fuel.REFERENCES[1] S. Serkowski, Ochrona powietrza i Problemy Odpadów, 6 (2003) 185-194[2] J. Mróz, Recykling i utylizacja materiałów odpadowych w agregatach metalurgicznych. Wyd. Pol. Cz., Częstochowa, (2006).[3] R. Koch, A. Noworyta, Procesy mechaniczne w inżynierii chemicznej. WNT, Warszawa (1998).[4] www.erich.com (5.05.2012)[5] J. Korol, D. Burchatr-Korol, Research Reports Mining and Environment, 1 (2010), 17–27[6] S. Serkowski, P. Izak, Szkło i Ceramika, 58 (2007), 31-37[7] J. Blatz, S. Serkowski, Hutnik – Wiadomości Hutnicze, 5 (2005), 288-292[8] K. Nowacki et al., Hutnik-Wiadomości Hutnicze, 5 (2006), 210-215[9] M. Karbowniczek et al., Hutnik – Wiadomości Hutnicze 7/8 (2005), 371-377[10] Lis T., Nowacki K., Metalurgija, 51 (2012)2, 257-260.[11] Białecka B., Adamczyk Z., Sposób oraz układ do utylizacji zaolejonych odpadów hutniczych. Patent PL 195967 B1[12] Instalacja odolejania odpadów hutniczych ﬁ rmy Eko-Fortuna sp. z o.o., patent application no P 395190 (10. 06. 2011)Note: P. Nowak is responsible for English language.

Methods of preparing deposits containing iron oxides for recycling

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