Competitive adsorption of organic solvents using modified and unmodified calcium bentonite clay mineral Temple Nwoburuigwe Chikwe*, Rose Etukudo Ekpo and Ifedi Okoye

ISSN: 2410-9649 Chikwe et al / Chemistry International 4(4) (2018) 230-239 iscientic.org. 231 www.bosaljournals/chemint/ editorci@bosaljournals.com INTRODUCTION The introduction and injection of harmful waste such as aromatics and petroleum products to the environment due to the current increase in petrochemical, agro-allied and petroleum industries has indeed constituted a severe threat to humans and animals. Steady and continual release of industrial effluent and waste into water bodies (oceans, rivers, seas, lake, and streams), results in the accumulation of pollutants and contaminants in sediments which are natural habitats of most aquatic lives (Aisien et al., 2013). Most of these toxins (pollutants) are also found in effluents released into the environment. Most aromatic compounds such as ethylbenzene, toluene and xylene are quite harmful and detrimental to humans, animals and the environment. The ingress of these aromatics into the water bodies make them unsuitable for consumption and also leads to total destruction of aquatic lives (Senturk et al., 2009). These aromatics especially ethylbenzene has the tendency to cause some adverse effect to human health such as mucous membranes irritation, impairment of the central nervous system, kidney impairment diseases, human liver disruption, skin irritation, eye irritation, destruction or total damage to the nervous system and also respiratory diseases (Berenjian et al., 2012). Petroleum products such as gasoline also known as petroleum motor spirit (PMS), dual purpose kerosene (DPK) and diesel also contain appreciable concentration of these aromatics as well as other harmful components making them also dangerous to humans and environment. Humans and environment gain undue exposure to petroleum products during oil spillage (Goncharuk et al., 2002). Owing to the aforementioned effects and the non-degradable properties of aromatics, there is an urgent need to adsorb aromatics such as ethyl benzene, xylene and toluene from wastewater before discharging to the surrounding (environment) in order to curtail and avert health implications. This can be achieved through the use of a locally available adsorbent with a relatively high surface area such as bentonite (Aisien et al., 2013). Bentonite is an aluminasilicate mineral clay that occurs naturally, it is primarily composed of montmorillonite mineral with a distinctive alumina octahedral sheet existing in between two tetrahedral sheets of silicon and it is globally found in most countries (Shen, 2000). Bentonite is a hydrophilic compound which swells when it absorbs water however several studies have been carried out on how to change the hydrophilic property of bentonite to organophilic property in order to make it a suitable adsorbent for organic compounds (Osalo et al., 2013). Organ ophilic bentonite or organo-modified bentonite can be synthesized by the exploitation of an organic acid and a quaternary ammonium compound (QAC) which are good modifying agents (Apemiye and Obi, 2010). Senturk et al., 2009 removed phenol from an aqueous solution with the aid of organophilic bentonite modified with cetyltrimethylammonium bromide (Senturk et al., 2009). The adsorption efficiency of bentonite can also be enhanced when treated with an acid, Obi and Okoye, 2014 utilized an acid modified bentonite for the removal of naphthalene from an aqueous solution (Obi and Okoye, 2015). The structure of bentonite is illustrated in Figure 1. There are several ways through which water contaminant and environmental pollutant such as ethylbenzene can be removed from petrochemical wastewater which include the utilization of modified zeolite, exploitation of organokaoline (Egbuchunam et al., 2016). Other means for ethylbenzene removal includes; the utilization of biological method, the use of physical method, the exploitation of chemical method, the application of catalytic oxidation, the employment of Ultraviolet (UV) oxidation, the utilization of bioscrubbers and the use of bio filters (Apemiye and Obi, 2010). However, this study is specifically on adsorption method using modified and unmodified calcium bentonite. Adsorption is a removal process in which an ion, atom or molecule known as the adsorbate from a liquid or gas adhere or attach itself to a liquid or solid surface called adsorbent. It can also be regarded as the concentration of adsorbate molecules on a molecular surface of a highly porous material such as bentonite, kaolin, activated charcoal, carbonized agro-waste material, zeolite and pillared clay (Mebrek and Derriche, 2010). During the adsorption process, the adsorbate particles are been attracted and held on the adsorbent’s surface by a weak force basically known as intermolecular force (Kralik, 2014). Exploration and production of crude oil have been the main contributor and the major source of economic growth in Nigeria and the utilization of imported bentonite as a hydrocarbon adsorbent during wastewater treatment has been capital intensive, it is therefore of utmost importance to reduce the importation of bentonite, hence the need to explore and provide an alternative adsorbent that is produced locally and is environmentally pleasant and friendly. The aim of this study is to determine the efficiency and effectiveness of modified and unmodified calcium bentonite clay in the removal of organic solvents from aqueous solution through the process of adsorption. Fig. 1: Structure of bentonite ISSN: 2410-9649 Chikwe et al / Chemistry International 4(4) (2018) 230-239 iscientic.org. 232 www.bosaljournals/chemint/ editorci@bosaljournals.com MATERIAL AND METHODS The calcium bentonite used for this study was obtained from Mansid Nigeria Limited, Port Harcourt Rivers State, Nigeria. Dodecyltrimethylammonium bromide (DTAB), mxylene, toluene and ethylbenzene were purchased from SigmaAldrich Company, Switzerland at >98% purity. The petroleum products were obtained from Nigerian National Petroleum Cooperation (NNPC), Port Harcourt, Rivers State, Nigeria. Equipment used include FT-IR Spectrometer, UVVisible Spectrometer, electrical oven, magnetic stirrer / hot plate, mechanical shaker, auto sieve machine and weighing balance Preparation of calcium bentonite The calcium bentonite sample was crushed and thereafter sieved using a 150 um sieve to obtain a homogenized powdered mixture. The powdered form was completely used for the study. Modification of calcium bentonite A measured amount of 10g of the milled calcium bentonite was soaked in 200ml of distilled water for 24 hours after which the bentonite-water mixture was properly stirred for 30 minutes before 0.8M of dodecyltrimethylammonium bromide (DTAB) was gradually added to the bentonite-water mixture and was subsequently stirred, heated and refluxed for two hours at temperature of 75oC. Upon the completion of the process of modification, filtration was carried out and the organo – modified bentonite was oven dried at a temperature of 110 oC. The dried DTAB modified bentonite was properly stored and preserved in a sample tube for characterization and batch adsorption. The whole process was repeated for different concentration of DTAB (Tina and Robin, 2014). Characterization of calcium bentonite The test samples (calcium bentonite) were characterized using a number of techniques such as FT-IR analyses, foster swelling test, adsorption capacity measurement and batch adsorption experiment using Ultraviolet Spectrometric analyses