Please cite this article in press as: A.A. Oladipo, M. Gazi, Nickel removal from aqueous solutions by alginate-based composite beads: Cen- tral composite design and artificial neural network modeling, J. Water Process Eng. (2014), http://dx.doi.org/10.1016/j.jwpe.2014.12.002 ARTICLE IN PRESS G Model JWPE-98; No. of Pages 11 Journal of Water Process Engineering xxx (2014) xxx.e1–xxx.e11 Contents lists available at ScienceDirect Journal of Water Process Engineering journal h om epage: www.elsevier.com/locate/jwpe Nickel removal from aqueous solutions by alginate-based composite beads: Central composite design and artificial neural network modeling Akeem Adeyemi Oladipo ∗ , Mustafa Gazi Department of Chemistry, Eastern Mediterranean University, Gazimagusa, TRNC via Mersin 10, Turkey a r t i c l e i n f o Article history: Received 15 September 2014 Received in revised form 5 December 2014 Accepted 6 December 2014 Available online xxx Keywords: Bentonite Acid dye Artificial neural network Nickel Central composite design a b s t r a c t Alginate-based composite bead (AB) was applied for the removal of Ni(II) ions from solutions in batch and fixed-bed systems. The reuse feasibility of the spent adsorbent was investigated for binding azo dye. Elovich kinetic model and mean adsorption energy (E) (13.2 kJ mol -1 ) indicated that Ni(II) ions removal followed ion-exchange mechanism. 98.5% removal for Ni(II) was observed at the maximum column operation (viz. 2.0 mL/min flow rate, 100.0 mg/L influent concentration and 9.0 g dose). Artificial neural network (ANN) and central composite design (CCD) models were applied to elucidate the complex adsorption process, and the finding is consistent with the experimental data. Desorption efficiency (DE) was noted to be higher when HCl (DE = 92%) was used as desorbing agent compared to NaOH (DE = 6%) in the first cycle. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Increasing industrial activity lately has led to the release of heavy metal infected effluent into freshwater systems, which is a serious threat to the environment and biota [1]. Industrial process such as electroplating, leather, textile, galvanization and batteries production have contributed to the occurrence of life-threatening pollutants in drinking water, surface water and even groundwater. Heavy metals and dyes are the most undesired pollutants released into the water bodies since tiny presence of dye can easily be detected by human eyes and, high concentration of heavy metals are undesirable to both human beings and aquatic animals. Nickel, the fifth most abundant element has been reported to be toxic and carcinogenic if accumulated above the World Health Organization (WHO) limit (0.1 mg/L) in drinking water [2]. Research has shown that the toxicology effects of acid dyes are obvious due to their ability to induce sensitization in humans as a result of the dye complex structure [3]. Acid red 25 (AR) is an azo dye extensively used in various industries and exposure to a considerable amount of AR is responsible for life-threatening dis- eases [4]. There are few reports dealing with the removal of nickel ∗ Corresponding author. Tel.: +90 392 630 2136; fax: +90 392 630 3039. E-mail addresses: akeem.oladipo@emu.edu.tr (A.A. Oladipo), mustafa.gazi@emu.edu.tr (M. Gazi). from aqueous media compared with other heavy metals; hence it is necessary to eliminate the threat as efficient as possible. Adsorption process using adsorbents is regarded as economic, simple and efficient technique for decontamination of wastewa- ter [1–4]. Researchers have suggested the various adsorbent to remove heavy metals/dyes from aqueous solutions [3–7]. However, low performance, high cost and poor regeneration/reutilization of spent adsorbent have led to the search for efficacious adsorbent [8]. Many reports focused on the removal of heavy metals from aqueous media while few researches have been directed to the utilization of the spent adsorbents which normally constitute secondary pol- lution. Bentonite has been used in this research due to its ion-exchange capability, availability, excellent surface and structural properties compared to other clays [8–10]. The bentonite’s adsorptive fea- tures can be attributed to the negative charges on its surface which emanated from the substitutions of metal ions (Al 3+ and Mg 2+ ) within the clay octahedral sheets making it suitable for adsorption of heavy metals [10]. Even though bentonite exhibits specific selec- tivity reaction with cations (M + ), its separation from aqueous media and regeneration after spent has limited its industrial application [8]. The surface of the natural bentonite used in this study was modified with HCl to enhance its ion-exchange capability and encapsulated within the matrix of alginate (biopolymer) to improve the overall structural integrity of the adsorbent and for easy sep- aration after use [8,11]. In our previous study [8], AB was utilized http://dx.doi.org/10.1016/j.jwpe.2014.12.002 2214-7144/© 2014 Elsevier Ltd. All rights reserved.