Optimization, equilibrium and kinetic studies of Zn 2þ and Ni 2þ adsorption from aqueous solutions using composite adsorbent Haider M. Zwain, Mohammadtaghi Vakili and Irvan Dahlan ABSTRACT A novel RHA/PFA/CFA composite adsorbent was synthesized from rice husk ash (RHA), palm oil fuel ash (PFA), and coal fly ash (CFA) by modified sol-gel method. Effect of different parameters such as adsorbent dosage, contact time, and pH were studied using batch experiment to optimize the maximum zinc (Zn 2þ ) and nickel (Ni 2 ) adsorption conditions. Results showed that the maximum adsorption condition occurred at adsorbent amount of 10 g/L, contact time of 60 min, and pH 7. At this condition, the removal efficiencies were 81% and 61% for Zn 2þ and Ni 2þ , in which the adsorption capacities (q max ) were 21.74 mg/g and 17.85 mg/g, respectively. Adsorption behavior of RHA/PFA/ CFA composite adsorbent was studied through the various isotherm models at different adsorbent amounts. The results indicated that the Freundlich isotherm model gave an excellent agreement with the experimental conditions. Based on the results obtained from the kinetic studies, pseudo-second- order was suitable for the adsorption of Ni 2þ and Zn 2þ , compared to the pseudo-first-order model. The results presented in this study showed that RHA/PFA/CFA composite adsorbent successfully adsorbed Zn 2þ and Ni 2 . Haider M. Zwain College of Water Resources Engineering, Al-Qasim Green University, Al-Qasim Province, Babylon, Iraq Mohammadtaghi Vakili State Key Joint Laboratory of Environment Simulation and Pollution Control, Beijing Key Laboratory for Emerging Organic Contaminants Control, School of Environment, Tsinghua University, Beijing 100084, China Irvan Dahlan (corresponding author) School of Chemical Engineering, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, Nibong Tebal, 14300 Nibong Tebal, Malaysia and Solid Waste Management Cluster, Science and Engineering Research Centre, Universiti Sains Malaysia, Engineering Campus, Seri Ampangan, Nibong Tebal, 14300 Nibong Tebal, Malaysia E-mail: chirvan@usm.my Key words | adsorption isotherm, adsorption kinetic, composite adsorbent, nickel, zinc INTRODUCTION The increased concentrations of heavy metals in the environment are a global problem. The World Health Organization (WHO) is concerned about drinking water that contains heavy metals like aluminum, manganese, chro- mium, cobalt, iron, nickel, zinc, copper, mercury, lead, and cadmium (WHO ). A part of that, Zn 2þ and Ni 2þ are among the most highly toxic heavy metals. Even at extre- mely low concentration, Ni 2þ presents an environmental threat and causes cancer of lungs and nasal sinus (Ahmedna et al. ). On the other hand, Zn 2þ is important for humans in small quantities, but it can affect health when the prescribed limit is exceeded. The World Health Organiz- ation (WHO ) has limited the concentrations of Zn 2þ and Ni 2þ to 3 mg/L and 0.07 mg/L, respectively. Most Zn 2þ and Ni 2þ enters the environment from various indus- trial effluents including cadmium–nickel batteries, lead and cadmium ores, purifying zinc, coal burning and burning of wastes, steel production, phosphate fertilizers, mining, alloy, pigments, and stabilizers (Low & Lee ). There are many techniques available for heavy metals’ removal such as adsorption reverse osmosis, solvent extrac- tion, ion exchange and precipitation. Among these, adsorption using activated carbon is a well-known tech- nique for heavy metals’ removal, but the high cost of this technique limits its large-scale application in developing countries. In addition, many other adsorbents have been 279 © IWA Publishing 2018 Journal of Water Supply: Research and Technology—AQUA | 67.3 | 2018 doi: 10.2166/aqua.2018.150 Downloaded from https://iwaponline.com/aqua/article-pdf/67/3/279/658763/jws0670279.pdf by guest on 31 May 2020