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Removal of Copper Ions from Aqueous Solutions by a Steel-Making By-Product F.A

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Removal of Copper Ions from Aqueous Solutions by a Steel-Making By-Product F.A ARTICLE IN PRESS Water Research 37 (2003) 3883–3890 Removal of copper ions from aqueous solutions by a steel-making by-product F.A. Lopez*,! M.I. Mart!ın, C. Perez,! A. Lopez-Delgado,! F.J. Alguacil Department of Primary Metallurgy and Materials Recycling, National Centre for Metallurgical Research (CENIM), CSIC, Avda. Gregorio del Amo, 8, 28040 Madrid, Spain Received 11 October 2002; received in revised form 10 April 2003; accepted 14 April 2003 Abstract A study is made of the use of a steel-making by-product (rolling mill scale) as a material for removing Cu2+ ions from aqueous solutions. The influence of contact time, initial copper ion concentration and temperature on removal capability is considered. The removal of Cu2+ ions from an aqueous solution involves two processes: on the one hand, the adsorption of Cu2+ ions on the surface of mill scale due to the iron oxides present in the latter; and on the other hand, the cementation of Cu2+ onto metallic iron contained in the mill scale. Rolling mill scale is seen to be an effective material for the removal of copper ions from aqueous solutions. r 2003 Elsevier Ltd. All rights reserved. Keywords: Copper; Steel-making by-product; Rolling mill scale; Cementation; Adsorption 1. Introduction membrane processing and electrolytic methods, etc. [3–10,24–26]. The effluents generated by modern industries (petro- Rolling mill scale is a steel-making by-product from steel leum refineries, non-ferrous metal works, motor vehicles, hot rolling processes and is basically composed of iron aircraft plating and finishing, etc.) generally have a oxides and metallic iron with variable oil and grease complex composition which includes metals (ions or contents [11,12]. Its specific production is about 35–40 kg/t complexes), suspended solids and other components [1,2]. of hot rolled product and Spain generates 0.044 Mt/year of According to the more stringent environmental laws, mill scale [11]. The oil component in rolling mill scale these effluents must be decontaminated because of their makes its recycling difficult, and its direct reuse in sintering hazardousness to humans, animals and plants. Metals are may lead to environmental pollution problems. Mill scale non-biodegradable and can accumulate in living tissues, with a high oil content is recycled after extracting the oil in thus becoming concentrated throughout the food chain. a pre-treatment stage or is dumped. Coarse scale with a With regard to the removal of inorganic pollutants particle size of 0.5–5 mm and an oil content of less than (e.g. metals), several techniques have been proposed for 1% can be returned to the sinter strand without any pre- their processing, such as precipitation, flotation, ion treatment. High oil contents (>3%) result in increased exchange, solvent extraction, adsorption onto different emissions of volatile organic compounds and potentially adsorbents—activated carbons, agricultural by-pro- also of dioxins and can lead to problems in waste gas ducts, natural zeolites, clays, manganese nodules, purification systems (e.g. glowfires in electrostatic pre- materials containing carbon, etc.—cementation on iron, cipitators). Because of this, mill scale needs to be pre- treated before it can be reused. Fine scale sludge consists mainly of very small scale particles (o0.1 mm). Because *Corresponding author. Tel.: +34-91-553-89-00; fax: +34- the fine particles adsorb oil to a very high degree (5–20%), 91-534-74-25. this scale cannot normally be returned to the sinter strand E-mail address: fl[email protected] (F.A. Lopez).! without pre-treatment [13]. 0043-1354/03/$ - see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0043-1354(03)00287-2 ARTICLE IN PRESS 3884 F.A. Lopez! et al. / Water Research 37 (2003) 3883–3890 The use of different industrial by-products as adsor- The surface composition was studied by means of bent materials in processes involving the removal of X-ray photoelectron spectroscopy (XPS) using a multi- metals from aqueous effluents has recently begun to be technique surface analysis unit, XPS-AES, with a VG developed, with the aim of seeking alternative ways of Microtech MT500 pumping station with double Mg/Al recycling certain by-products and at the same time anode, operating at 15 kV and 20 mA. The Mg Ka1,2 line finding cheaper replacements for expensive conventional (1253.6 eV) was used for all analyses. The working sorbent materials in different situations [14–18]. With pressure in the analysis chamber was o10À8 mbar. Peak specific regard to by-products from the steel-making positions were corrected for surface charging using the industry, blast furnace sludge has been studied as an C1s peakat 284.8 eV as a reference. Prior to analysis, adsorbent material for certain metallic ions in aqueous samples were cleaned in an Ar stream. solution [19,20,3], given that its iron oxide and carbon Morphological analysis of the mill scale samples contents confer it a high adsorption/absorption capa- before and after the adsorption tests was carried out city. Other steel-making by-products, such as blast by scanning electron microscopy (SEM), using a Jeol furnace slag [21] and electric furnace slag, have more JXA-840 unit equipped with an energy dispersive X-ray recently been studied as sorbing materials for the analyser (EDAX) with which the element composition removal of metallic ions from aqueous solutions [7]. of the studied samples was determined. An X-ray This workinvestigates the capacity of rolling mill fluorescence study by wavelength dispersion was also scale to remove Cu2+ ions from aqueous solutions. carried out, mapping the Fe and Cu contents in order to see their distribution in the mill scale. The samples were prepared by embedding the powder in a polymer resin and then polishing its surface and metallising it with graphite. 2. Materials and methods For the adsorption experiments the mill scale was dried at 80C for 24 h and then passed through a screen, using The mill scale used in this workwas supplied from a only the o0.5mmfractioninthetests.Cu2+ solutions hot rolling mill in an electric steel shop in northern were prepared by dissolving Cu(NO3)2 Á 2.5H2Oin0.01M Spain. The mill scale was dried at 80 C for 24 h, NaNO3, in order to maintain a constant ionic strength of revealing an initial moisture content of 5%. the dissolution. 100 mL of the metal solution was added to For the purpose of analysis, the mill scale was crushed a fixed amount of mill scale (10 g). The initial pH was to obtain a grain size of o40 mm. The chemical pHi=5.0070.01. To determine the rate constant, tests composition of the ground sample was determined by were carried out at several temperatures (between 20C X-ray fluorescence analysis by wavelength dispersion and 80C) for different reaction times (0–6 h) with an (WDXRF) using a Philips PW-1404 spectrometer. aqueous solution of 50 mg/L Cu (II). Removal tests were Carbon and sulphur analyses were carried out by performed at different temperatures (between 20Cand combustion in a Leco CS-244 oven and infrared 80C) for an equilibrium time of 5 h, using aqueous detection. solutions whose concentration varied between 5 and The analysis of iron in its different states of oxidation 8000 mg/L Cu (II). The equilibration time was established (Fe3+,Fe2+ and Fe0) was performed by titrating with a prior to conducting equilibration experiments. The equili- 2+ 0.1 N K2Cr2O7 solution. For the analysis of Fe and brium pH was pHeq=(6.00–6.50)70.01. The samples were Fetotal the mill scale was dissolved in HCl with a few stirred constantly by means of a Hucoa-Erloss Lauda MS- drops of HF. Barium diphenylamine-sulphonate was 20 B thermostatically controlled. The pH was controlled used as indicator. For the determination of metallic iron using a Crison 517 pH-meter. The resulting suspensions (Fe0) the sample was previously dissolved in a bromo- were filtered and the solutions analysed by atomic methanol solution, separating the dissolved metallic iron absorption spectrophotometry (AAS) in a Perkin-Elmer (soluble in bromo-methanol) by filtration. Filtering was 1100B spectrophotometer. The amount of copper ad- carried out with a filtering crucible of 20 mm, with the sorbed on the mill scale was determined by the difference solubilised Fe0 passing into the filtrate and the Fe2+ and between the initial concentration and the equilibrium Fe3+ (insoluble ions in bromo-methanol) being retained concentration (or the concentration at each time). in the filter [22]. The crystalline mineralogical composition was deter- mined by X-ray diffraction (XRD) using a Siemens 3. Results and discussion D-5000 diffractometer (Cu Ka radiation). The N2 adsorption isotherm was determined at 77 K 3.1. Characterisation of rolling mill scale for a mill scale sample previously degasified at 60C and 10À5 Torr for 120 min, using a Coulter SA-3100 unit. Rolling mill scale is a material of a laminar morphol- 2 The isotherm data was used to determine the value of ogy and low specific surface area (SBET ¼ 0:43 m /g). the BET specific area. It is comprised mainly by a mixture of iron oxides: ARTICLE IN PRESS F.A. Lopez! et al. / Water Research 37 (2003) 3883–3890 3885 100 90 80 °C ° 80 60 C 40 °C 70 20 °C 60 50 40 Copper adsorption (%) 30 20 10 0 0123456 Reaction time (h) Fig. 1. Variation in copper adsorption percentage on mill scale with time at several temperatures. C0 ¼ 50 mg/L Cu (II), mill scale concentration 100 g/L. Table 1 Rate constants for different temperatures and copper concentration on the mill scale and in the equilibrium solution (t ¼ 5h) 2 2+ T ( C) k (cm/s) R Cu(ads) (mg/g) [Cu ]aq (mg/L) 20 1.6 Â 10À8 0.971 0.09 39.9 40 6.8 Â 10À8 0.975 0.24 2.2 60 4.2 Â 10À7 0.971 0.49 1.2 80 8.0 Â 10À7 0.973 0.50 0.1 [Cu](aq) (mg/L) 0.00 40.00 80.00 120.00 160.00 200.00 50.00 1.40 1.20 40.00 1.00 [Cu](ads) (mg/g) 30.00 0.80 0.60 20.00 80 °C 60 °C [Cu](ads) (mg/g) 40 °C 0.40 20 °C 10.00 0.20 0.00 0.00 0.00 1000.00 2000.00 3000.00 4000.00 [Cu](aq) (mg/L) Fig.
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