Removal of Ni ( II ) and Pb ( II ) ions from aqueous solutions by grapefruit ( Citrus paradisi ) Mesocarp Biomass

The surface characteristics of Citrus paradisi (grapefruit mesocarp biomass) on the biosorption of Ni (II) and Pb (II) ions from aqueous solution were studied adopting a batch reactor technique. The dried grapefruit mesocarp biomass was characterized using phytochemical screening and Fourier Transform Infra – Red (FTIR) Spectroscopy. The results of the characterization revealed the presence of alkaloids, tannins, saponins, cyanogenic glycosides. Furthermore, the FTIR spectrum pattern of the biomass showed broad and sharp absorption peaks indicating the existence of functional groups like – OH, C=O, C-H, C-O, N-H, etc. The biosorption process was found to be pH, time and concentration dependent. The rate of biosorption was higher in Ni (II) ion than Pb (II) ion. The result of the equilibrium modeling showed that the biosorption process fitted well with the Freundlich isotherm equation indicating a muiltilayer biosorption. The mechanism of the biosorption process followed pseudo – second – order kinetic model equation with correlation coefficient (R 2 ) of 0.999 for Ni (II) ion and 0.991 for Pb (II) ion respectively. Thermodynamic parameters determined showed that the biosorption of Ni (II) and Pb (II) ions on the surface of the biomass was an exothermic and spontaneous process. The rate of biosorption was found to decrease with increasing temperature. The results showed that the dried grapefruit mesocarp biomass was efficient and effective in the biosorption of Ni (II) and Pb (II) ions and is recommended to be applied in wastewaters. © JASEM http://dx.doi. org/10.4314/jasem/v19i3.13 INTRODUCTION The degradation of natural waters with several heavy metal contaminants, have been found to be emanating mostly from mining waste and industrial discharges (Baig et al., 1999). These toxic materials cause problems to the entire ecosystem. Although some heavy metals are necessary for the growth of plants, aquatic lives and humans, after certain concentration, it becomes lethal to plants, microorganisms and humans. Heavy metal pollution has become a global issue owing to the fact that it threatens human health and the ecosystem. Their presence over permissible levels in drinking water may cause adverse effects on human biochemical dynamics (Dahiya et al., 2008). These metals may come from different sources such as electroplating, textile, smelting, mining, glass and ceramic industries as well as storage batteries, metal finishing, petroleum, fertilizer, pulp and paper industries (Aksu, 2001). Heavy metals are not biodegradable and tend to accumulate in living organisms (Kobya, 2005). Water pollution due to heavy metals contamination is an issue of great environmental concern (Vasuderan et al., 2003). In Nigeria today, greater percentage of its citizenry depend on treated sachet and bottled water as the major source of drinking water. Therefore, there are a lot of health related challenges coming out due the consumption of contaminated water. The effect of heavy metals on man cannot be neglected because exposure to these contaminants even at low concentration in the environment can cause severe dysfunction in the renal, reproductive and central nervous systems (Manaham, 2004). Lead is a major harmful pollutant to the biosphere, and even trace amount of it pose a detrimental risk to human health. In the recent times, the Northern part of Nigeria has recorded over 400 deaths due to lead poisoning. Nickel on its own also has toxic effect on human, animals and plants. As a result of the increasing environmental concern for these contaminants, there has been serious interest in the removal of heavy metals from contaminated soils and waste waters. A number of technologies have been developed over the years to 436 Removal of Ni (II) and Pb (II) ions from aqueous solutions 1 OBI, C; 1 NJOKU, OE remove toxic metals from water. The most important of these techniques include chemical precipitations, electro – flotation, ion – exchange, reverse osmosis and adsorption on activated carbon (Gaikward, 2004). These methods of water treatment are expensive and sometimes ineffective especially when metals are present in solution at very low concentration except for adsorption technique (Baig et al., 1999). An emerging field of interest is employing natural, agricultural and agricultural by – products as biosorbents for the removal of heavy metals from aqueous solution. Removal rates of 80% or higher can be expected with biosorption process. Biosorption is also able to achieve this removal in hours and sometimes even minutes; thereby potentially reducing or eliminating the high cost associated with other technologies (Mack et al., 2007). Many agricultural wastes that are available at low cost have been reported to be capable of removing substantial amounts of metal ions from aqueous solutions (Igwe et al., 2005; Gardea – Torresdey et al., 2005). The exchange properties of these agricultural wastes can be attributed to the presence of carboxylic, phenolic, hydroxylic, cyano groups, etc (Babarinde et al., 2013). These functional groups attract and sequester metal ions. Grapefruit popularly known as ‘fruit from the paradisi’ (Citrus X paradisi) mesocarp residue possesses these chemical characteristics and it is inexpensive and environmentally friendly (Willamson, 1997). Literature showed scanty information on the characterization and biosorptive properties of the grapefruit mesocarp. It was therefore explored in the present study as a biosorbent for the removal of heavy metals – nickel (II) and lead (II) ions from aqueous solution. The data generated was modeled using two isotherm equations namely; Langmuir and Freundlich isotherms adsorption model equations respectively. The mechanism of the biosorption process and thermodynamic quantities was evaluated. MATERIALS AND METHODS Characterization: Functional group elucidation was done on the grapefruit mesocarp biomass using Fourier Transform Infrared (FTIR) Spectrophotometer. Phytochemical screening for tannins was carried out using the method described by Evans and Trease, (2009) while glycosides, alkaloids by Sofowora, (1993) and saponins by Harborne, (1973). Biomass preparation: Grapefruits were harvested from the farm of Mr. Ekechukwu of Elekenaowasi Obohia in Imo State. It was washed with deionized water and peeled to obtain the mesocarp. The mesocarp was air – dried, ground and sieved using 250 μm mesh size sieve. The grapefruit mesocarp was used without any chemical treatment for the sorption studies. Preparation of the biosorbates: All the chemicals used in this study were of analytical grade. A stock solution of lead (II) and nickel (II) ions of concentration 1000 mg/L was prepared by dissolving 1.6 g of Pb(NO3)2 and 4.24 g of Ni(CH3CO2)2.H2O in 1 dm 3 of distilled water. Serial dilution of the stock solution was carried out to obtain working concentrations of Pb (II) and Ni (II) ions. Batch biosorption study: The biosorption study was determined by batch experiments. The biosorption studies were conducted at room temperature to determine the effect of pH, contact time, initial metal ion concentration, and the effect of temperature (using thermo – stated water bath). The residual metal ion concentrations of the filtrate of each metal solution were analyzed using Buck Scientific Model 210 VGP Atomic Absorption Spectrometer (AAS). All experiments were conducted for a period of 60 mins except for the contact time where the time was varied. The amount of the metal ion biosorbed per gram of the biomass is calculated using the expression in equation [1] below: