Browsing by Author "Mdoe, James Epiphan Gabriel"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Studies on the adsorption capacity and kinetics of lead and gold ions on activated carbons prepared from Tanzanian agro wastes
    (University of Dar es Salaam, 1995) Mdoe, James Epiphan Gabriel
    An investigation has been made on adsorption capacity and kinetics of lead and gold on activated carbons prepared from some carbonaceous agrowastes . Cashew nut shells, coconut shells, rice husks and black wattle charcoal (from acacia mearnsii plant) were used in preparation of the carbons. While rice husks were activated chemistry at 1000 k using KOH, the other source materials including a non-agrowaste, bituminous coal were carbonized and then activated at 1200K using CO2. The activated carbons wee characterized by a static volumetric technique, and their BET surface areas ranged from 200 to 1000 m2 g-1. The agrowaste based carbons were microporous. Whereas the bituminous coal based carbons possessed some wider pores. Evaluation of mineral impatiens showed the carbons to have percentages ash ranging from 1.2 to 36,1. A quantitative determination of gold adsorption capacity on the carbons has shown that, type of source materials, level of carbon burn-off, temperature and composition of the adsorption media affect the adsorption process. The adsorption capacities obtained ranged from 32 to 90 mg gold per g carbon; rice husks based carbons showing the lowest values. Low temperature and high percentage carbon burn-off (about 60/% ) were found to give high adsorption results. The equilibrium adsorption data were correlated well by freundlich and Langmuir isotherm equations. Adsorption of lead was mainly influenced by solution PH. The adsorption was found to start at approximately 3 PH units before hydrolysis and precipitation of the lead: PH 4 being the minimum for maximum adsorption. In the alkaline region the adsorption efficiency on all activated carbons except those from rice husks reached about 100z. The adsorption kinetics of the two metals on the activated carbons was found to be of similar pattern; being very fast in the first hour and then decreasing slowly as the adsorption approaches equilibrium. The data were best described by laidera et al model.