Modeling mono- and multi-component adsorption of cobalt(II), copper(II), and nickel(II) metal ions from aqueous solution onto a new carboxylated sugarcane bagasse. Part I: Batch adsorption study

Highlights

• Co²⁺, Cu²⁺, and Ni²⁺ were removed from aqueous medium by modified sugarcane bagasse.

• Bagasse was modified with trimellitic anhydride via esterification reaction.

• The adsorption of Co²⁺, Cu²⁺, and Ni²⁺ was studied in mono- and bi-component systems.

• The removal of metal ions by the adsorbent is governed by ion-exchange mechanism.

• All metal ions were fully desorbed from the adsorbent using 1 mol/L HNO₃ solution.

Abstract

A new carboxylated-functionalized sugarcane bagasse (STA) was prepared through the esterification of sugarcane bagasse with trimellitic anhydride. The optimized synthesis conditions yield STA with a percent weight gain of 73.9% and the number of carboxylic acid groups accounted for 3.78 mmol/g. STA was characterized by FTIR, elemental analysis, TGA, PZC, and SEM. Adsorption kinetics followed a pseudo-second-order model. The adsorption rate constant showed the following order: k_2,Ni²⁺ > k_2,Cu²⁺ > k_2,Co²⁺. Four mono- and multi-component isotherm models were used to model the adsorption systems. Monocomponent experimental data were fitted to Langmuir and Sips models; whereas, multicomponent data were fitted to modified extended Langmuir and P-factor models. The maximum adsorption capacities (Q_max,mono) obtained from the Langmuir model were 1.140, 1.197, and 1.563 mmol/g for Co²⁺, Cu²⁺, and Ni²⁺, respectively. The competitive studies demonstrated that the multicomponent adsorption capacity (Q_max,multi) was smaller than Q_max,mono, as a result of the interaction between the metal ions. Desorption studies showed that all metal ions could be fully desorbed from STA.

Introduction

The Agency for Toxic Substances and Disease Registry (ATSDR, 2014) have classified some metals as toxic, persistent, and bioaccumulative elements. Among the most hazardous substances that impose risks to human health are various toxic metals (Ahmad and Prasad, 2011). Interestingly, arsenic (As), lead (Pb), and mercury (Hg) are the top three most harmful metals, followed by cobalt (Co), nickel (Ni), and copper (Cu) at positions 51, 57, and 118, respectively (Ahmad and Prasad, 2011, ATSDR, 2014). Such toxic metals are present in the ionic form in waste streams from mining operations, tanneries, batteries, electronics, electroplating, and petrochemicals as well as in textile and pesticide mills (Amin et al., 2013, Fu and Wang, 2011, Kazemipour et al., 2008). Toxic metals are some of the major pollutants in marine, soil, solid industrial wastes, and untreated industrial wastewaters. Both solid and liquid industrial wastes can be considered as major sources of innumerous types of metals found in soil, groundwater, and water bodies (Amin et al., 2013, Kazemipour et al., 2008). The discharge of industrial effluents containing large amounts of toxic metals into the environment without suitable treatment has resulted in serious environmental problems (Amin et al., 2013, Barakat, 2011, Soetan et al., 2010).

Co, Cu, and Ni are all micronutrients for plants, animals, and humans (Ahmad and Prasad, 2011, Soetan et al., 2010). They participate in prosthetic groups and as co-factors of many enzymes and are, therefore, essential; however, at high concentrations, they can cause several serious health problems in humans (Ahmad and Prasad, 2011). The toxic effects of Co, Cu, and Ni are well documented (Klaassen, 2008).

Various physicochemical methods have been suggested for the removal of metal ions from industrial wastewaters such as electrochemical and chemical precipitation, ultrafiltration and nanofiltration, ion exchange, and reverse osmosis (Fu and Wang, 2011, Kazemipour et al., 2008). Such methods can be adopted alone or in combination, such as chemical precipitation followed by nanofiltration (Fu and Wang, 2011). Such processes have significant drawbacks, such as incomplete removal, high-energy requirements, and production of toxic sludge that needs to be treated and disposed (Barakat, 2011).

Recently, various studies have reported the development of cheaper and more effective technologies, aiming to decrease the amount of wastewater produced and enhance the standard quality of the treated effluent (Barakat, 2011, Fu and Wang, 2011). Adsorption has become one of the cheaper alternative treatments, as the search for low-cost adsorbents (modified or not) with a metal ion-binding capacity has been intensified (Bhatnagar and Sillanpää, 2010, Miretzky and Cirelli, 2010, Sun, 2010, Wan Ngah and Hanafiah, 2008). Agricultural by-products are promising candidates as effective adsorbents, owing to their low cost and availability throughout the world (Kumar, 2006). Among the most important low-cost agricultural by-products is sugarcane bagasse (SB). It is largely available in countries such as Brazil, China, and India, where it is a by-product from the sugar and bioethanol mills. Among these countries, Brazil is the world’s largest producer of sugarcane (Ferreira et al., 2015). SB is mainly composed of cellulose (42.19 ± 1.93%), hemicelluloses (27.60 ± 0.88%), lignin (21.56 ± 1.67%), ash (5.63 ± 2.31%), and extractives (2.84 ± 1.22%) (Rocha et al., 2015). The three major components of SB are rich in primary and secondary hydroxyl groups that can be used to graft functional groups with a metal ion-binding capacity (Wan Ngah and Hanafiah, 2008).

This study aimed to prepare a new adsorbent with an improved metal ion-binding capacity from chemical modification of SB with trimellitic anhydride (TA). TA is a commercial and stable reagent. After esterification with SB, it releases two carboxylic acid groups that can form complexes with different metal ions. The chemical modification of SB was intensively studied and optimized. The new adsorbent material was used to study the removal of Co²⁺, Cu²⁺, and Ni²⁺ from spiked monocomponent and multicomponent aqueous solutions. The influence of time, pH, and metal ion concentration on adsorption was studied in detail. Desorption and reuse of the spent adsorbent was also evaluated.