RESEARCH ARTICLE Binding of some heavy metal ions in aqueous solution with cationized or sulphonylated starch or waste starch Katja Lappalainen 1 , Johanna K€ arkk€ ainen 1 , Annu Rusanen 1 , Tiia-Riikka Wik 1 , Matti Niemel€ a 1 , Asier Goitia Madariaga 1 , Sanna Komulainen 1 , Riitta L. Keiski 2 and Marja Lajunen 1 1 Sustainable Chemistry Research Unit, University of Oulu, Finland 2 Environmental and Chemical Engineering Research Group, University of Oulu, Finland Contamination of water by heavy metal ions is a severe environmental problem. In this study, starch- or waste-starch-based binding agents were used to bind heavy metal ions in aqueous solutions in order to prevent the precipitation of metals in alkaline conditions (pH 10). This is a useful feature, e.g. when ultrafiltration is used as a purification technique for a low metal concentration containing wastewaters. The studied binding agents were water-soluble cationized depolymerized barley starch (CDS) prepared by depolymerization and subsequent cationization, sulphonylated starch (SS) and cationized depolymerized potato peel waste (CW), all of which have not been used previously as binding agents. The studied modified starches were investigated in the binding of Fe(III), Cu(II), Zn(II), or Ni(II) ions in aqueous solutions by utilizing inductively coupled plasma-optical emission spectrometry (ICP-OES) as an analytical method. Cationized depolymerized starch bound 80–100% of Fe(III), Zn(II), and Cu(II) ions and SS bound 85–95% of Fe(III), Zn(II), and Ni(II) ions when 0.5 mM metal ions solutions and molar ratio of starch:metal 0.66:1 were used. Cationized depolymerized waste starch bound Cu(II) ions 78–94% (0.25–2.5 mM metal ion solutions prepared with distilled or lake water) in aqueous solution with molar ratio of starch:metal varying from 1:1 to 3:1. Received: August 27, 2015 Revised: February 15, 2016 Accepted: February 15, 2016 Keywords: Cationized starch / Ionic liquid / Metal ion binding / Potato peel waste / Sulphonylated starch 1 Introduction Wastewaters contaminated with heavy metal ions are a global problem. Heavy metal ions have a high water-solubility and can therefore be absorbed by living organisms. Through food chain, they can further enter and accumulate in human body, where they can lead to serious health problems [1, 2]. Due to the toxicity of metallic pollutants many fields of industry are obligated to treat their effluents. Several techniques are used for the removal of heavy metal ions from aqueous solution, i.e. chemical precipitation, ion-exchange and electrochemical treatment. However, these conventional techniques can have significant dis- advantages [3, 2]. Sorption is another technique used to remove heavy metal ions from aqueous solutions. The most important commercially used sorption materials include activated carbon, polyacrylamide and polyethylenimine. However, activated carbon is expensive and synthetic polymers are often petroleum-based, poorly biodegradable materials, which may contain toxic or even carcinogenic additives or monomeric residues. Therefore, the development of safer and more economical materials is needed [3–6]. Recently, there has been a growing interest towards natural polymers like starch as alternative, cheap and effective adsorbents for heavy metal ions [7]. Globally, starch is one of the most abundant natural polymers. It is a low-cost, nontoxic, renewable and biodegradable storage carbohy- drate, which consists of anhydroglucose units (AGU) and is produced in all photosynthesizing plants. Each AGU of starch contains approximately three hydroxyl groups, which Correspondence: Prof. Marja Lajunen, Sustainable Chemistry Research Unit, University of Oulu, P.O. Box 3000, Finland 90014. E-mail: marja.lajunen@oulu.fi Fax: þ358-8-5531629 Abbreviations: CDS, cationized depolymerized starch; CS, cationized starch; CW, cationized depolymerized potato peel waste; SS, sulphonylated starch DOI 10.1002/star.201500229 Starch/Stärke 2016, 68,1–9 1 www.starch-journal.com ß 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim