Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-018-3618-z RESEARCH ARTICLE - CHEMICAL ENGINEERING The Removal of Cr(VI) from Aqueous Solution by Activated Carbon Prepared from Apricot, Peach Stone and Almond Shell Mixture in a Fixed-Bed Column ¸ Seyma Yüksel 1 · Ramazan Orhan 1 Received: 22 May 2018 / Accepted: 29 October 2018 © King Fahd University of Petroleum & Minerals 2018 Abstract The purpose of the study is to remove Cr(VI) from aqueous solutions in a fixed-bed column under different operating conditions [pH, influent Cr(VI) concentration, flow rate, bed height and temperature]. To this end, activated carbon prepared of apricot, peach stones and almond shell mixture was used. Adsorption capacity increased with the increase in bed height and influent Cr(VI) concentration, while it decreased with the increase in flow rate, pH and temperature. The adsorption capacity was found as 6.67mg/g under optimum conditions. Adams–Bohart, Thomas and Yoon–Nelson models were applied to experimental data to find the kinetic parameters. It was determined that the appropriate model describing the adsorption mechanism was Thomas. As a result, the new activated carbon used in this study indicates its applicability in the removal of Cr(VI) ions in industrial wastewater. Keywords Cr(VI) · Adsorption · Activated carbon · Fixed-bed · Triple mixture 1 Introduction Heavy metal pollutants in water are detrimental to human health, soil, plants and aquatic life [1]. Chromium (Cr) is a toxic metal found in natural waters as it is used in electroplat- ing, tanning, water cooling, pigment, dye, leather tanning, photography and chemical manufacturing industries [2]. Cr is found in two different stable oxidation stages such as Cr(III) or Cr(VI) in aqueous environments [3]. The latter is carcino- gen, teratogen and mutagen to biological systems and more lethal than the former [4]. The acceptable amount of Cr(VI) in drinking water and wastewater are 0.05 and 0.20mg/L, respectively, set by the WHO or USEPA guidelines [5]. Therefore, chromium wastewaters should be treated effec- tively prior to discharge into aquatic environments. There are different types of processes proposed for wastewater treatment such as adsorption, ion exchange, reverse osmosis, chemical precipitation, electrochemical precipitation, mem- B Ramazan Orhan rorhan@firat.edu.tr 1 Department of Chemical Engineering, Firat University, 23119 Elazig, Turkey brane filtration, oxidation/reduction, ultrafiltration, flotation and solvent extraction [6–13]. Although these available tech- nologies are efficient in the treatment of high concentrations of heavy metal ions, they are particularly ineffective in the treatment of metals (1–100 mg/L) at low concentrations in the solution or are very expensive [14]. In addition, these advanced technological processes have the disadvantages, such as can not be adequately treated of metals, expensive equipment needs, more amount of chemicals and high energy requirements and formation of toxic sludge as a result of the process [15]. One of those processes is adsorption, which is operative, easy to apply and cost-effective [16]. There are many recent studies that used different adsorbents for removal of Cr(VI) ions by using batch adsorption experiments, but depending on wastewater and adsorbent properties, adsorption in fixed-bed columns (FBCs) is generally a preferred method for industrial wastewater treatment. Data obtained from column experi- ments are also helpful for the industrial implementation of the method [17,18]. The term “breakthrough curve” (BC) is employed for the determination of fixed-bed column efficacy. The breakpoint time (BT) and shape of BC are very impor- tant characteristics that provide insight into the performance of adsorption columns [19]. 123