546 J. Eng. Technol. Sci., Vol. 49 No. 4, 2017, 546-559 Received July 12 th , 2017, Revised August 11 th , 2017, Accepted for publication October 30 th , 2017. Copyright ©2017 Published by ITB Journal Publisher, ISSN: 2337-5779, DOI: 10.5614/j.eng.technol.sci.2017.49.4.9 Removal of Copper (II) Ions in Aqueous Solutions by Sorption onto Fly Ash Lita Darmayanti 1,2,* , Suprihanto Notodarmodjo 1 & Enri Damanhuri 1 1 Department of Environmental Engineering, Faculty of Civil and Environmental Engineering, Institut Teknologi Bandung, Jalan Ganesa No. 10, Bandung 40132, Indonesia 2 Civil Engineering Department, Universitas Riau, Kampus Bina Widya Simpang Baru, Pekanbaru Riau 28293, Indonesia *E-mail: litadarmayanti@eng.unri.ac.id Abstract. The ability of fly ash to adsorp Cu(II) ions from two different coal combustion systems was studied. Optimum removal was found at pH 5, contact time 30 minutes and 60 minutes for Fly Ash 1 and Fly Ash 2, respectively, and dosage 10 g/l. The difference in adsorption capacity between both fly ashes may be due to their carbon fraction and CaO content. The removal of Cu (II) ions was caused by both adsorption and/or precipitation. Precipitation is enhanced by lowering the carbon fraction and increasing the CaO content. The adsorption isotherm showed that the Langmuir model fitted well to the experimental data of both fly ashes. A thermodynamic study was conducted at three different temperatures: 25 °C, 45 °C, and 60 °C. The adsorption processes were spontaneous and endothermic and were more favorable at higher temperature. Keywords: adsorption; aqueous solutions; Cu ions; fly ash; Langmuir model. 1 Introduction Human activities release heavy metals into the hydrosphere in many different ways, such as effluent of industries, transportation, municipal sewage, land filling, mining, etc. Heavy metals can pollute the environment and cause public health problems. It is important to eliminate heavy metals from water because these elements are not biodegradable and tend to accumulate in living organisms, inducing various diseases and disorders. Some metals, like Hg, Pb and Cr, are very toxic to organisms, while others, like Fe, Mn, Cu, Zn, Ni and Co, even though essential for living beings, when present in excess of certain limits can be very harmful. Copper is highly toxic because it is bio- accumulative and persistent. It does not break down in the environment and is carcinogenic [1-3]. There are many processes suitable for the removal of metals from water, such as chemical precipitation, coagulation, biological systems, oxidation with ozone/hydrogen peroxide, ion exchange, photocatalytic degradation, and