Pb(II) Adsorption onto Urea Treated Leucaena leucocephala Leaf Powder: Characterization, Kinetics and Isotherm Studies

The use of Leucaena leucocephala leaf powder treated with urea (treated-ULLP) as an alternative adsorbent for the adsorption of Pb(II) ions has been investigated. The adsorption studies were performed under batch mode and focused on the effects of pH, adsorbent dosage and initial Pb(II) concentrations. The pseudo-second order kinetics model fitted well the adsorption data with the values of correlation coefficient (R2) > 0.97. Large amounts of hydroxyl, carboxyl and amine as detected by the Fourier transform infrared (FTIR) spectrophotometer suggested that these functional groups were responsible for the adsorption of Pb(II) ions. Treated-ULLP demonstrated a good potential for Pb(II) ions removal with the maximum adsorption capacity of 90.09 mg/g, calculated from the Langmuir isotherm model. INTRODUCTION A lot of heavy metals are released into the environment, which include copper (Cu), chromium (Cr), lead (Pb), zinc (Zn), cadmium (Cd), nickel (Ni), manganese (Mn), and mercury (Hg) (Babarinde et al., 2006). Volesky (2001) stated that lead [Pb(II)] is one of the most toxic metals that has gained major attention due to its health impact on humans. Pb(II) could be stored in human tissues such as kidney and liver and can pose health hazards even in small concentrations (Puranik & Pakniker 1997). Pb(II) may originate from different types of industrial activities such as electronic, fossil fuel, painting, mining, automobile, sewage wastewater and fertilizer (Singh et al. 2008). A few decades ago, various conventional methods such as ion exchange, filtration, chemical precipitation, reverse osmosis, and electro deposition have been applied to remove Pb(II) from industrial wastewaters (Zheng et al. 2008). However, these treatments suffered some limitation such as production of sludge at the end of the treatment process (Papandreou et al. 2007), and less effective at trace levels of Pb(II). So, adsorption is an alternative process which has several advantages such as low cost, simple, more effective and records a high adsorption capacity value (qmax). A variety of adsorbent materials have been applied to remove Pb(II) from aqueous solutions, which include activated carbon, zeolites, resins and plant wastes. Leucaena leucocephala leaves was used in this study because it contains various organic compounds such as lignin, cellulose, hemicellulose, polyphenols, protein, lipids, flavonoids, mimosine and tannins (Zarin et al. 2016), which can act as the active sites for Pb(II) adsorption. The main objectives of this work were to evaluate the parameters that could influence the uptake of Pb(II) on urea treated L. leucocephala leaves, to determine the rate of Pb(II) adsorption based on kinetics models, and to determine the maximum adsorption capacity based on the Langmuir isotherm model. MATERIALS AND METHODS Materials Leucaena leucocephala leaves were collected in Jengka, Malaysia. The leaves were brought to the lab and washed several times with deionized water. The leaves were dried in an oven overnight at 353 K. Then, the leaves were ground and sieved to obtain the particle size of 180-355 μm. Working solutions of Pb(II) were prepared from a 1000 mg/L Pb(II) stock solution and diluted to desired concentrations using deionized water. The chemical treatment of L. leucocephala leaf powder was performed according to the method proposed by Kong et al. (2014). In brief, 3 g of L. leucocephala leaf Nat. Env. & Poll. Tech. Website: www.neptjournal. com Received: 27-06-2019 Accepted: 30-08-2019