Removal of boron from aqueous solution using

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Removal of boron from aqueous solution using calcined magnesite tailing .... cined magnesite tailing were carried out using X-ray fluorescence analyzer ..... [21] Y.S. Ho, G. McKay, Sorption of dye from aqueous solution by peat, Chem. Eng.

Chemical Engineering Journal 189–190 (2012) 68–74

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Removal of boron from aqueous solution using calcined magnesite tailing I˙ lker Kıpc¸ak, Mine Özdemir ∗ Department of Chemical Engineering, Eskis¸ehir Osmangazi University, 26480, Eskis¸ehir, Turkey

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Article history: Received 21 October 2011 Received in revised form 7 February 2012 Accepted 8 February 2012 Keywords: Boron removal Adsorption Calcined magnesite tailing Isotherm Kinetics

a b s t r a c t The present work was undertaken to explore the effectiveness of using calcined magnesite tailing for removal of boron ions from aqueous solutions. The effects of calcination temperature, initial pH, adsorbent dosage, contact time and temperature on boron removal were studied. The optimum calcination temperature was 600 ◦ C and the optimum pH was 6.0. The contact time was about 420 min to reach adsorption equilibrium. The experimental data were analyzed by Langmuir and Freundlich equations. The Langmuir isotherm model was found to describe adequately the adsorption process. Pseudo first order kinetic model, pseudo second order kinetic model and intraparticle diffusion model were used to describe kinetic of boron adsorption onto calcined magnesite tailing. The experimental data fitted very well the pseudo second order kinetic model. The boron adsorption was determined to be endothermic in nature and thermodynamically favorable. The results showed that calcined magnesite tailing is a suitable adsorbent for the removal of boron from aqueous solutions. © 2012 Elsevier B.V. All rights reserved.

1. Introduction The elemental form of boron is unstable in nature, and boron is found mainly in the form of boric acid or borate salts in nature. Boron exists in the form of boric acid (H3 BO3 ) in acidic and neutral media. Boric acid behaves as a weak Lewis acid in aqueous solution (pKa = 9.24). It accepts hydroxide ion from water and releases a proton into solution. In alkali medium, boric acid begins to transform to borate ion (B(OH)4 − ), and above the pH value of 9.24 the dominant species of boron is the borate ion. Boric acid and borate exist as monomers in solution at low concentrations (0.025 M), and they form polyborate species at higher concentrations [1–3]. Boron is used in many industrial products, such as glass, ceramics, detergents, and semiconductors. Borax, refined hydrated sodium borates, boron oxide, boric acid and perborates are commercially significant boron compounds [1–4]. During the production of these boron compounds, borax wastes containing high boron concentration are formed in borax plants. These are discharged to the plant area and the ponds. Boron compounds in these wastes pass to the soil because of rainfall. Thus, boron compounds can eventually be introduced into a drinking water source and lead to some serious health and environmental problems. The acceptable daily intake of boron is 18 mg/day for an average body weight of 60 kg [3]. Hence, World Health Organization (WHO) recommends a drinking water standard of 0.5 mg L−1 for boron [5]. In European Union, its recommended content is 1.0 mg L−1 for drinking water [3]. The boron

∗ Corresponding author. Tel.: +90 222 2393750x3677; fax: +90 222 2393613. E-mail address: [email protected] (M. Özdemir). 1385-8947/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2012.02.025

contents in these wastewaters and waters must be removed by a suitable method. The common methods for boron removal from water are mainly adsorption, ion exchange, and membrane processes. Adsorption is a more useful and economical technique at low boron concentrations. Natural minerals and tailings are potential low-cost adsorbents for the adsorption of toxic species [6–15]. Magnesite has the chemical formula of MgCO3 and it is the primary source for production of magnesium and its compounds. These products are widely used in many fields from basic refractory bricks to pharmaceuticals and from catalysts to fertilizer industries. The natural magnesite contains some impurities such as silicon, iron and calcium. In the magnesite plants in Turkey, natural magnesite is generally beneficiated by crushing, screening, scrubbing and magnetic separation. The tailings from these plants still contain a significant amount of usable magnesite, but at a very low grade (MgO equivalent of 35% to 39%). These tailings containing large amounts of impurities are currently simply accumulated in the plant areas. It is highly desirable therefore to utilize the magnesite tailings in order to avoid environmental problems [16].Magnesite, calcite and dolomite were investigated for use as potential adsorbents for the removal of heavy metals and boron from solutions [8–15]. However, there does not exist any study on the use of calcined magnesite tailings as an adsorbent for removal of boron from water. The objective of the study is to investigate the use of calcined magnesite tailing for the removal of boron from aqueous solutions. The effects of different parameters such as calcination temperature, pH, contact time, adsorbent dosage and temperature on the removal of boron were investigated. The data were evaluated by some kinetic

I˙ . Kıpc¸ak, M. Özdemir / Chemical Engineering Journal 189–190 (2012) 68–74

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Table 1 Chemical compositions of original and calcined magnesite tailing. Component (%, w/w)

MgO

SiO2

CaO

Fe2 O3

Al2 O3

MnO

K2 O

P2 O5

Na2 O

TiO2

L.O.I.

Original Calcined

37.80 50.70

11.17 15.39

6.25 8.80

0.77 1.17

0.13 0.19

0.05 0.07

0.01 0.02

0.01 0.01

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