College of Natural and Applied Sciences

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Browsing College of Natural and Applied Sciences by Subject "Absorption and adsorption"

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    Adsorption of heavy metal ions on organosilica composites prepared using rice husks ash as a silica source
    (University of Dar es Salaam, 2014) Ligate, Fanuel Josephat
    Triaminopropyl-silica hybrids were prepared via post synthetic technique using Rice Husks Ash (RHA) as silica source and (3-trimethoxysilylpropyl) diethylenetriamine. The prepared materials were characterized by acid titration, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX) spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), nitrogen adsorption-desorption analysis and thermogravimetric analysis. Results show that the amine group loading of the triaminopropyl-silica hybrid prepared using rice husks ash (TSH-R) was 2.15 mmol/g. The TSH-R was found to have characteristic functional groups, namely, O-Si-O (900-1150 cm-1), CH (2800-3000 cm-1), O-H (3000-3500 cm-1) and N-H (1530 cm-1) which were obtained by ATR-FTIR analysis. SEM and FE-SEM micrographs of the prepared materials showed rough surfaces with protuberances, cracks and holes. The RHA, rice husks silica (RHS) and TSH-R materials had average particle sizes of 336.8, 296.4 and 1054.1 nm, respectively. EDX gave the elemental composition whereby Si and O were present in high proportion in all samples. The BET surface areas of RHA, RHS and TSH-R were 17.8, 20.2 and 5.7 m2/g respectively. The total pore volumes were 0.43 cm3/g for RHA, 0.49 cm-3/g for RHS and 0.02 cm3/g for TSH-R. On the other hand, the average pore width of RHA, RHS and TSH-R were 95.9, 97.6 and 17.3 nm respectively. The materials had pores in the mesoporous range and exhibited very small change in weight beyond 500 ºC. Adsorption studies of Ni(II), Zn(II), Pb(II), Cu(II) and Co(II) ions showed that RHA and TSH-R were good adsorbents with the average maximum adsorption of 99 and 95% for RHA and TSH-R, respectively when 1.0 g of adsorbent and initial metal ions concentration of 21 - 27 mg/L at pH 4 were employed. Both Langmuir and Freundlich isotherms indicated that the adsorption was favorable. Thus RHA and TSH-R can be used to remove mixtures of toxic heavy metals from contaminated water. Based on the findings of this study RHA is the best adsorbent because, it has overall superior adsorptive properties and it is cost effective.
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    A study on biosorption of heavy metals using seaweed eucheuma denticulatu
    (University of Dar es Salaam, 2014) Sharif, Hamad Maalim
    The ability of seaweed species Eucheuma denticulatum to remove Cr(VI) and Pb(II) from aqueous solutions was investigated in a batch system by using AAS. The influence of pH, contact time and initial concentration of the metals on the uptake byE. denticulatum were investigated. The study revealed that the optimum pH for Pb(II) and Cr(VI) uptake were 4.0 and 3.0, respectively, whereas the optimum contact time for the metals adsorption was about 120 min. Pb(II) and Cr(VI) uptakes of 4.7 and 0.91 mg/g, respectively, were attained at optimum pHs, 28 ℃ and 3 hrs contact time. Cr(VI) uptake increased with the increase in initial Cr(VI) concentration and reached saturation at 200 mg/l. Pb(II) uptake also increased with the increase in initial Pb(II) ions concentration. However, beyond 1000 mg/l the rate of increase in Pb(II) uptake slowed down. Pb(II) uptake was found to decrease by 4.37% and 3.48% on addition of Na+ and Mg2+ ions in concentration range of 10 to 25 mg/l to the test solutions, respectively. Na+ and Mg2+ ions in Cr(VI) test solutions caused a decrease in Cr(VI) uptake by the biomass by 31.5% and 25.6% respectively. Desorption experiments indicated that 0.1 M CaCl2 was an effective elluant for the] recovery of Pb(II) from the biomass but not for Cr(VI). Regeneration of the metal loaded E. denticulatum by using 0.1 M HCl caused dissolution of the biomass. The biosorption of Pb(II) onto E. denticulatum fitted well to Langmuir isotherm with maximum adsorption capacity (qmax) of 416.67 mg/g while that of Cr(VI) fitted well to Freundlich isotherm with constants K and n values of 0.652 and 5.95, respectively. It can be concluded that E. denticulatum is an effective biosorbent for the removal of Pb(II) from aqueous solution but not for Cr(VI).