Received: 27 December, 2009. Accepted: 4 September, 2010. Original Research Paper Bioremediation, Biodiversity and Bioavailability ©2011 Global Science Books Effects of Adsorbent Activation on Bioremediation of Hg (II) and Cd (II) Ions from Aqueous Solution using Boiler Fly Ash Nnenna E. Okoronkwo * • Jude C. Igwe • Chibuike C. Aniekwu Department of Industrial Chemistry, Faculty of Biological and Physical Sciences, Abia State University, P.M.B. 2000 Uturu, Nigeria Corresponding author: * nnennaejijeokoronkwo@yahoo.com ABSTRACT Heavy metal (HM) removal from wastewater has attracted much attention in the past few decades. The search for low cost sorbents became the focus recently as a result of the expensive nature of conventional adsorbents. The use of unactivated and nitric acid activated boiler fly ash an agricultural by-product in the bioremediation of mercury (Hg) (II) and cadmium (Cd) (II) ions from aqueous solution was investigated in this work. The amount adsorbed increased as the initial metal ion concentration was increased. For unactivated boiler fly ash (BFA), the amount of Hg (II) ion adsorbed was higher than the amount of Cd (II) ion that was adsorbed. The acid-activated BFA adsorbed more than the unactivated BFA, with the influence of activation much more on the amount of Cd (II) ion adsorbed. The sorption process was modeled using two kinetic models: pseudo-first order and the pseudo-second order equations; and also six isotherm models namely Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin, Harkins-Jura (H-J) and Smith equations. For the kinetic models, the pseudo second-order equation gave a better fit to the sorption process. The differences in fitness of the isotherm models to the sorption process were not significant by two-way ANOVA. Also, analysis of the equilibrium sorption data in accordance with the six isotherm models and applying a normalized standard deviation q revealed that the Harkins-Jura isotherm model gave a better fit to experimental data. The apparent energy of sorption E (KJ mol -1 ) from the D-R equation gave values of 26.72, (unactivated), 223.61 (activated) for Cd (II) ion and 50.00 (unactivated), 158.11 (activated) for Hg (II) ion, all in KJ mol -1 . Hence, activation increased the sorption capacity of the adsorbent and the values of apparent energy of sorption. Also, from the values of E, the sorption process could be said to follow a chemisorption mechanism. _____________________________________________________________________________________________________________ Keywords: adsorption, agricultural by-products, environment, heavy metal ions, isotherms, surface chemistry Keywords: BFA, boiler fly ash; HM, heavy metal INTRODUCTION The treatment of effluent water from industries and other sources have been achieved through adsorption principles. In recent times the use of agricultural residues or waste materials in the removal of HM ions has revealed good pot- ential in wastewater treatment (Brandley and Duong 1988; Sun and Shi 1998; Igwe and Abia 2003; Okoronkwo 2008). This recent research and development of agricultural waste materials as adsorbents are based on a need to increase utility and for better adaptation of renewable materials to specific ends in order to make better use of limited resour- ces available and to meet with consumers’ needs and wishes compared to the use of ion exchanged resin, precipitation and other conventional methods which are also effective methods of removing metals from effluent water, but which are costly (Brandley and Duong 1988; Lin and Liu 2000). Heavy metals (HMs) are poisonous metallic elements in the environment. The toxicity of HMs to marine life and consequently to man has for many years been established. Cadmium (Cd), a naturally occurring HM can be found in food, water and cigarette smoke. It is a known human carci- nogen. Exposure of people to Cd may not only be through foods but also through drinking contaminated water (Sun and Shi 1998). Mercury (Hg) is one of the most problematic of all toxic HMs because despite its dangerous and known roles as a neurotoxin, many people have it implanted in their mouth, injected into their blood stream or are con- suming it daily in fish. The removal of these HMs from solution by unmodified and modified cellulosic materials such as maize cob has been reported (Okeimen and Oriaki 1987; Okeimen and Okundaye 1989; Igwe and Abia 2003; Abia et al. 2005). Similar works have been carried out by researchers which include the removal of lead from aqueous solution by palm kernel fiber (Ofomaja et al. 2005), the use of polyami- nated highly porous chitosan (Takatsuji and Yoshida 1998), the use of chemically modified and unmodified waste (Abia and Igwe 2005). Furthermore the role of pH, temperature and particle size effect of some of these biosorbents has been investigated (Ho 2003; Igwe et al. 2005). Also sorp- tion kinetics and intraparticulate diffusivities of Cd, Pb, and Zn ions on maize cob have been reported (Abia et al. 2005). The modeling of some of these biosorbents with an adsorp- tion isotherm has been shown to follow some well known isotherms. Boiler fly ash (BFA), which is a porous substance, results from the burning of mainly fruit bunch and kernels for boiler fuel. It is known that every tonne of fresh fruit bunch (FFB) produces about 4 to 6 kg of BFA (Majid et al 1999). BFA has also been reported to be made up of phos- phorus (0.28-1.33%), potassium (1.02-4.31%), calcium (0.39-3.24%) and magnesium (0.29-2.60%) (Rusnani and Ma 1999). BFA has been applied as a soil conditioner because of these mineral contents. It has also been used as a landfill because its generation has been enormous from the numerous palm oil mills that exist. BFA have also been used in various other ways such as an adsorbent for removal of HMs from aqueous solution (Pandy et al. 1985; Mathur and Rupainwar 1988; Weng and Huang 1994; Hashim et al. 1996) and in the reduction of BOD, TSS and colour from palm oil mill effluent (POME) (Majid et al. 1999). Therefore, this work aimed to investigate the effect of concentration of these HMs on the adsorption capacity of ®