Available online at www.scholarsresearchlibrary.com Scholars Research Library Archives of Applied Science Research, 2012, 4 (5):2161-2173 (http://scholarsresearchlibrary.com/archive.html) ISSN 0975-508X CODEN (USA) AASRC9 2161 Scholars Research Library Removal of Pb 2+ and Ni 2+ ions from aqueous solutions by adsorption onto activated locust bean (Parkia biglobosa) husk Nathaniel Oladunni, Edith B. Agbaji and Sulaiman O. Idris Department of Chemistry, Faculty of Science, Ahmadu Bello University, Zaria, Nigeria _________________________________________________________________________ ABSTRACT Locust bean husk (LBH) activated with H 3 PO 4 was used as an adsorbent to remove Pb 2+ and Ni 2+ from aqueous solution. The effects of varying initial metal ion concentration and adsorbent dose on the adsorption capacity were identified through laboratory experimental investigations. An equilibrium adsorption experiment at ambient temperature was carried out and the experimental data of adsorption fitted into Langmuir and Freundlich adsorption models. The result showed that the amount of metal ion adsorbed onto activated LBH increases with an increase in the initial metal ion concentration. In the given time duration of 2hours and at the initial metal ion concentration of 100ppm, Pb 2+ and Ni 2+ showed their highest uptake value of 19.85mg/g(79.4%) and 11.10mg/g(57.1%) respectively. For the effect of adsorbent dosage, the maximum adsorbent capacity was at a dosage of 0.8g, recording adsorption capacity of 4.07mg/g for Pb 2+ and 2.94mg/g for Ni 2+ . Langmuir model having higher R 2 values of 0.961 and 0.952 for Pb 2+ and Ni 2+ respectively fitted the equilibrium adsorption data better than the Freundlich model for the two metals. Keywords: Activated locust bean husk (LBH), Heavy metals, Wastewater, Isotherm, Sorption ____________________________________________________________________________________________ INTRODUCTION Water pollution may be due to various sources, namely, from sewage, industrial wastes or pesticides runoff from farm land. Such water if supplied directly to consumers without treatment may lead to the spread of waterborne diseases. Some specific pollutants include industrial chemicals such as chlorinated hydrocarbons, heavy metals, including cadmium, lead, chromium, arsenic, mercury and nickel, saline water, bacterial and industrial waste [1]. Among these pollutants, the contribution of heavy metals to environment is of major concern because of its toxicity, bioaccumulation, persistence and non-biodegradable nature. Some of the techniques which have been used in the removal of heavy metals from effluents include ion exchange, chemical precipitation, electrodialysis, electrolytic extraction, reverse osmosis, and cementation. These methods are expensive and in addition have the inability to remove metals at low concentration [2,3]. Compared with the aforementioned techniques, adsorption has proved to be less expensive alternative for the removal of metals from aqueous solution [4]. Literature has indicated the potential of some agricultural waste products as inexpensive sorbents. Due to their low cost, after these materials have been expended, they can be disposed of without causing environmental degradation [5]. The aim of this research is to study the adsorption of heavy metals (Pb 2+ and Ni 2+ ) from aqueous solutions by activated locust bean husk. This aim will be achieved by determining some physicochemical properties of the adsorbent and examining the adsorption capacity of activated locust bean husk for