Hexavalent chromium was adsorbed from aqueous solution with three prepared and characterized adsorbents, namely goethite (G), activated carbon (AC) and their composite (GAC). The goethite particle was synthesized using the precipitation methods, and activated carbon was prepared from the stem bark of Daniellia oliveri tree and composite in a ratio of 1:5 goethite-activated carbon. The adsorption capacities of G, AC and GAC for Cr(VI) are 6.627, 5.455 and 6.354 mg/g with 0.02 g adsorbent within

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... ontact time of 60, 180 and 30 min for G, AC and GAC, respectively, for Cr(VI) adsorption at optimum pH of 3. The isotherm studied was best explained by Langmuir adsorption isotherm and fitted with the pseudo-second-order kinetic model. Desorption studies showed that 1.0 M HNO 3 was a better desorbing agent than 0.1 M HNO 3 , 0.1 M HCl and 1.0 M HCl. Chromium was most desorbed (94.60% in Cr//G using 1 M HNO 3 ). The result obtained revealed that goethite and activated carbon produced are favourable adsorbents and the composite of the two adsorbents gives a more favourable, economical and affordable adsorbent for the clean-up of heavy metal contamination. 3 213 Page 2 of 18 effectiveness of adsorption process and cost-friendly. In the clean-up of wastewater, activated carbon from different agricultural waste materials has been used for purification, decolourization and removal of toxic heavy metal ions. The need to look for a cost-effective material to be used for the removal of pollutant from the environment has been the great impetus for the use of Daniellia oliveri stem bark for the preparation of activated carbon. The activated carbon composite with goethite particles will be used in the removal of toxic metals from aqueous solution. Experimental Collection and sample preparation Preparation of activated carbon Activated carbon was produced from the stem bark of Daniellia oliveri tree that grows around the Chemical Engineering Laboratory Building, University of Ilorin. The tree bark was washed, sun-dried and air-dried. This was followed by carbonization and activation with 75% H 3 PO 4 in the ratio H 3 PO 4 /char of 1.0.