Theses and Dissertation

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    Application of rice and corn husk biochar for removal of heavy metal ions from industrial wastewater
    (NM-AIST, 2020-01) Sanka, Paulo
    This study investigated the removal of heavy metal ions from industrial wastewater by using rice and corn husk biochar. The choice of the materials was influenced by their largest surface area, plentiful functional groups and their availability in the local environment. Rice and corn husks were pyrolysed at 500, 600, and 700 °C to make biochars that were used to treat low quality industrial wastewater. Carbonisation of rice husks at 600 °C produced the best removal efficiencies for Cr (65%), Fe (90%) and Pb (> 90%). The carbonisation of corn husks at 600 °C produced the worst removal efficiencies for Cr (only 20%) and Pb (slightly > 35%). Regardless of the carbonisation temperature, rice husk biochars performed better than corn husk biochars. All data fitted well in both the Langmuir and Freundlich isotherm models (R 2 values ranging between 0.82 and 0.99). The Langmuir separation factor RL was had negative values; probably due to the low initial concentration of the adsorbates in the raw wastewater. All the biochars showed a relatively short contact time (20 to 30 min) to attain maximum adsorption efficiencies – a promising feature for future industrial applications. The studied biochar materials from rice and corn husk have the potential to remove heavy metal ions from industrial wastewater; rice husk biochar showed higher removal capacity than corn husk.
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    Clay-based ceramic materials for water de-fluoridation
    (NM-AIST, 2021-08) Leonidas, Wilson
    Long-term consumption of water with fluoride concentration above the WHO recommended limit of 1.5 mg/g may cause fluorosis. Low-income communities living in fluoride endemic regions are more affected as they cannot afford well-established water de-fluoridation technologies. Currently, clay ceramic materials impregnated with silver colloids have been used to disinfect water disregarding the removal of fluoride. This work investigated improving the de-fluoridation capacity of clay ceramic materials with in-situ generated Ca/Mg phosphate system using locally available carbonate rocks as a source of Ca/Mg. To achieve this, clayCa/Mg phosphate system composite ceramic materials were synthesized from varied ratios of clay (K) to carbonate rock materials (R) (K:R = 0:100, 90∶10, 85∶15, 75∶25 and 100:0), sintered at various temperatures between 500 and 900 . The materials were characterized using XRF, FTIR, AAS, CHNS-O analyzer and X-ray PDF analysis. The three types of carbonate rock materials investigated were identified to be; high-calcium limestone, magnesium-deficient dolomite and near-stoichiometric dolomite. The magnesium-deficient dolomite gave rise to a Ca/Mg phosphate system that exhibited superior de-fluoridation performance. The material improved in de-fluoridation performance with increase sintering temperature from 500 to 700 , possibly due to an increase in the more soluble magnesium-substituted tri-calcium phosphate (β-Mg x Ca 3-x PO 4 ), CaO and MgO (PDF and FTIR). This work has shown that the de-fluorination performance of clay ceramic materials can be improved with a phosphate system synthesized/formed in-situ using carbonate rocks as Ca/Mg source. The method of improving the de-fluoridation performance of clay ceramic materials introduced in this present study has potential applications in the fabrication of water filters with fluoride removal ability.