ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY http://dx.doi.org/10.14233/ajchem.2016.19424 INTRODUCTION Contamination of the aquatic environment by metal has become an important issue with respect to the environment and human health. In recent years, studies directed to quantify the adsorption of toxic and heavy metals from subsurface environment, industrial and research wastes through sorption [1]. In the nuclear fuel, processing steps cycle generates wastewater streams containing a variety of dissolved metals, including lanthanide and actinide elements. The origin of this problem is the continuous production of huge volume, low activity and waste requiring permanent and efficient treatment. Environmental protection by remediation of toxic metals and radionuclides from aqueous solutions, has been studied exten- sively, because of their hazardous even at low concentration [2]. When dealing with uranium contamination of the environ- ment, special interests are raised. High mobility is the major concern with uranium as it is highly soluble and occurs in the hexavalent form as a mobile hydrated uranyl ion in the pH ranges of acid rain. If it is present at a concentration above 0.1 mg/kg of body weight, uranium can cause transient chemical damage to the kidney [3]. Solid Phase Extractive Pre-Concentration of Uranium(VI) from Liquid Waste onto Peach Stone Steam Pyrolysis Activated Carbon H.M.H. GAD 1,* , T.F. MOHAMMADEN 2 and M.A. MAHMOUD 2 1 Hot Labs & Waste Management Center, Egyptian Atomic Energy Authorities, P.O. 13759, Cairo, Egypt 2 Nuclear Materials Authority, Cairo, Egypt *Corresponding author: E-mail: hamdigad22@gmail.com Received: 20 June 2015; Accepted: 20 August 2015; Published online: 30 December 2015; AJC-17686 Drinking water contaminants, especially heavy metals and uranium, have been recognized as a worldwide problem pose a serious threat to human health. Among several treatment technologies applied for contaminant removal, adsorption methods have been studied extensively and proven to offer satisfactory results with high selectivity. In this study, steam pyrolysis activated carbons from biomass were synthesized with characterizations giving a higher capacity for uranium and other heavy metal contaminants. In this study, a batch equilibration pre- concentration of uranium(VI) was carried out in the pH range (2-10), adsorbent dosage (0.166-0.833 g L -1 ), sorption time (5 min to 24 h), temperatures (25, 50 and 70 °C), different types of activated carbon precursor, uranium initial concentration (50-500 mg L -1 ) and different interfering ions (cations: Cr, Pb, Fe, K and anions: NO3 - , Cl - , SO4 2- , HPO4 2- ). The equilibrium data fitted well to the Freundlich and Langmuir equilibrium models in the studied concentration range and temperatures. The kinetics of the adsorption process followed a second-order adsorption and intra-particle diffusion is not the only rate determining step. 0.25 M H2SO4 was effective in uranium recovery. The results indicated that the conversion of naturally abundant peach stone of the nuisance value to valuable material exhibited considerable potential for application in pre-concentration and separation of uranium from aqueous solution. Keywords: Pre-concentration, Uranium(VI), Liquid waste, Peach stone, Steam pyrolysis activated carbon. Asian Journal of Chemistry; Vol. 28, No. 4 (2016), 751-760 Physical, physico-chemical and chemical principles are different techniques adopted by various researchers for pre- concentration of uranium [4-6]. Preconcentration techniques have come to the forefront compared to other solid phase extraction (SPE) or solid-liquid extraction (SLE) due to the following advantages. Higher pre-concentration factors are included, the emulsion is absent, with respect to hazardous samples it is safe, due to low consumption of reagents it has a minimal cost, flexibility and easier incorporation into automated analysis techniques [7,8]. Neutral polymer-Amberlite XAD series [9-11], octadecyl silica membrane discs, silica [12,13], activated silica gel [4], polyurethane foam [14], controlled pore glass and cationic or anionic exchange resins [15-19] as a number of solid. Sorbents have been reported for the pre- concentration of uranium(VI) from dilute solutions prior to determination by a variety of analytical techniques. Bearing in mind high retention capacity, ready availability, the ease of elution and regeneration and efficient applicability to pre- concentration of trace amounts of inorganic, activated carbon were chosen as a solid phase extraction sorbent in the present study. Tailored activated carbons were reported for the sorption of Cu, Mn, Co, Cd, Pb, Ni, Cr and lanthanides. To our best of