Department of Biological and Environmental Sciences

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Browsing Department of Biological and Environmental Sciences by Subject "Characterized"

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    Adsorption Kinetics and Isotherms of Methylene Blue by Geopolymers Derived from Common Clay and Rice Husk Ash
    (Physical Chemistry, 2017-10-07) Maingi, Francis M.; Mbuvi, H. M.; Ng’ang’a, M. M.; Mwangi, H.
    With the onset of industrialization mankind has witnessed various environmental issues in the society. Industrialization has not only brought development and prosperity but eventually disturbed the ecosystem. It is currently estimated that 1.1 billion people in the world lack access to enhanced clean water supplies. Consequently, pursuance of sustainable materials and technologies for wastewater remediation is critical. Use of adsorbents for wastewater treatment is preferable due to their simplicity and cheap materials involved. Geopolymers are synthesized hydrothermally using alumina and silica which possesses amorphous surface for use as adsorbents. There is adequate information and reports in literature that indicate clay contain alumina and silica. Similarly, findings have shown that rice husk ash contains substantial amounts of silica. This work reports synthesis of geopolymers GP-1, GP-2 and GP-3 prepared by using different SiO2/Al2O3 ratios and consequently equilibrium and kinetics behaviour of adsorption of methylene blue. The geopolymers were characterized using FT-IR, EDS, XRD and SEM. Geopolymer adsorbents were subjected to methylene blue batch sorption experiments thate indicated the adsorption of MB increased with increased Si/Al ratio in geopolymers. The adsorption isotherms were described by Langmuir, Freundlich, Temkin and Sips isotherms. Data for adsorption of MB onto geopolymers fitted best in Sips adsorption model. Kinetic studies showed that Pseudo -second order model were more suitable than the Pseudo- first order model in explaining the kinetics of adsorption.
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    Clay-Rice Husk Ash based Geopolymers for Remediation of Pb (II) and Cd (II) from Wastewater
    (Egerton Journal of Science & Technology., 2019-10-31) Maingi, Francis M.; Mbuvi, Harun Mbatha; Ng'ang'a, M M; Mwangi, Henry
    Industrialization and technological advancements have led to the generation of numerous pollutants such as heavy metals into the aquatic ecosystem. These toxic compounds are extremely dangerous to human health and the environment due to their non-biodegradability, severe toxicity, ability to accumulate and contaminate ground and surface waters. Subsequently, pursuance of sustainable materials and technologies for better attainment of environmental sustainability is critical. This study reports the synthesis of geopolymers GP-1, GP-2 and GP-3 from different clays. Geopolymers were hydrothermally synthesized using clay and rice husks waste as an alumina and silica source respectively. The geopolymers were characterized using Fourier transform-infra red, energy dispersive spectrometry, X-ray diffraction and scanning electron microscope. Batch and gravitational column experiments using Pb (II) and Cd (II) ions were carried out. Increased metal ion uptake was recorded with raised Si/Al ratio of the adsorbents. The mean percentage uptake of 90.23 ± 0.4 and 89.63 ± 0.18 of Pb (II) and Cd (II) were achieved at pH of 4.0 and 5.0 respectively using GP-3. Langmuir, Freundlich and modified Langmuir Freundlich isotherms were used in equilibrium studies. Data for adsorption of Pb (II) and Cd (II) fitted best in the modified Langmuir Freundlich model. The highest adsorption capacities of Pb (II) and Cd (II) were 209.9 and 136.2 mg/g respectively, attained using GP-3. Based on the results obtained, geopolymers produced from common clay and rice husk waste displayed promising potentials in the removal of heavy metal ions from the aqueous phase. Considering the availability of raw materials for geopolymerization and the high metal ions uptake capacities of geopolymers, they can also be used as adsorbents for removal of heavy metals in industrial wastewater.