CHEMISTRY & CHEMICAL TECHNOLOGY Chem. Chem. Technol., 2021, Chemistry Vol. 15, No. 2, pp. 161–169 SUSTAINABLE ADSORPTION REMOVAL OF NICKEL AND CHROMIUM ON ECO-FRIENDLY INDUSTRIAL WASTE: EQUILIBRIUM STUDY Yehia H. Magdy 1 , Hossam Altaher 2, * , Anwar F. Al Yaqout 3 https://doi.org/10.23939/chcht15.02.161 Abstract. 1 Adsorption of nickel and chromium was investigated using fuller’s earth. The experimental data were analyzed using five 2-parameter adsorption models and three 3-parameter models. The maximum adsorption capacities for nickel and chromium were 769 and 556 mg/g, respectively. The Langmuir isotherm model was found to have the best fitting indicating monolayer adsorption. The adsorption was found to have an exothermic nature. Keywords: adsorption, chromium, fuller’s earth, isotherm, nickel, vegetable oil. 1. Introduction Nickel and chromium are classified by many agencies as two of the most toxic heavy metals [1, 2]. Discharge of wastewater containing them to the environment without proper treatment represents a serious threat to the environment. These metals are soluble in the aqueous environment, increasing their threats since they will be readily available to humans, animals, and plants [3]. Hexavalent chromium has severe adverse health effects starting from allergic reactions to mutagenic and carcinogenic problems [4]. Nickel has acute neurotoxic and carcinogenic effects and it was found to be embryotoxic and teratogen [5]. The high concentration of nickel may cause dermatitis, chronic bronchitis, kidney disease, gastrointestinal distress, liver impairment and cardiovascular disease [6-8]. Many industrial effluents contain various concentrations of these metals. Chromium is present in high concentration in industries such as leather tanning, paints and pigments, textile, ceramics, wood processing, 1 Department of Chemical Engineering, Faculty of Engineering, El- Minia University P.O. Box 61511, Egypt 2 Sustainable Solution Group, Al-Sharq, Ahmed Al-Jaber St., Al-Dira Tower, P.O. Box 17886, Khalidiyah 72459, Kuwait 3 Civil Engineering Department, Kuwait University, P.O. Box 5969, Safat 13060, Kuwait * haltaher@hotmail.com  Magdy Y., Altaher H., Al Yaqout A., 2021 electroplating, cooling, metal finishing, pulp and paper, cement manufacturing, alloy and steel manufacturing, fertilizer [9]. On the other hand, nickel can be found in the wastewater of many industries including electroplating, mining, smelting, paints, batteries, coinage, jewelry, stainless steel, and catalyst [10]. Various techniques are applied to remove metal ions from wastewater such as membrane technology, ion exchange, solvent extraction, chemical precipitation, coagulation/flocculation, electrochemical treatment, and adsorption [11, 12]. These methods have many disadvantages including generation of a considerable amount of sludge, high cost, and long-time required for such processes [13]. Among these several methods, adsorption has many advantages. The efficiency of removal even at low adsorbate concentration, the simplicity of operation, availability of adsorbents and possibility of their regeneration, low energy requirement are examples of the advantages of adopting adsorption as a removal techniques for many pollutants [14-18]. Several materials have been investigated by researchers as adsorbents [19]. However, it is very important to select the proper adsorbent that is suitable for the adsorption system under investigation. Such adsorbent must be cheap, efficient, and available in sufficient amount through the year [20, 21]. Fuller’s earth is natural widely available sedimentary clay that is known as bleaching clay. It belongs to the montmorillonite group having the general formula (OH 4 )Si 8 O 20 ·nH 2 O. In addition to montmorillonite, fuller’s earth may contain other constituents with different compositions including dolomite, quartz, and calcite. The crystal structure of montmorillonite is based on a three- layer type clay; two silica layers alternating with one alumina or silica layer [22]. Fuller’s earth is also a solid waste that is produced from vegetable oils industry. Its main use in that industry is as a bleaching agent. In such an industry, it is used just once. After the bleaching stage of vegetable oils, the spent fuller’s earth is separated by filtration and disposed of [23]. The worldwide generation of the spent bleaching material is estimated to be 2 million metric tons per year [23].