Development of adsorbents from rice residues for mercury removal process
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Date
2017
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Universiti Teknologi Malaysia
Abstract
Mercury is one of the heavy metals considered as a serious toxic to both human and the environment. Conventional treatment technologies for the removal of mercury commonly suffer some limitations like high operating cost, incomplete precipitation, and sludge generation. Adsorption which has been proven as an effective separation process for a wide variety of applications emerged as a solution. In this study, rice residues (rice husk and rice straw) were utilized as potential lowcost adsorbent for removing mercury from aqueous solution. The modification of adsorbent such as grafting with organosilane, carbonization and chemical activation process was carried out to enhance its adsorption capacity. The synthesized adsorbents were characterized using proximate analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, elemental analysis, nitrogen adsorption/desorption analysis and surface acidity test. The effects of operational parameters such as pH, initial concentration, contact time and temperature were investigated in batch adsorption experiment. The experimental data were correlated with several isotherm and kinetic models for the determination of the adsorption potential. Based on the analyses, the mercury adsorption process was mainly controlled by film diffusion and chemical process mechanism. It was found that samples RSGM (grafting with organosilane), RSCC300 (dry pyrolysis), RHT300 (wet pyrolysis) and RSACS (single-step acid activation) showed highest adsorption rate with 98.98 %, 98.96 %, 97.17 % and 99.12 %, respectively. The selected adsorbents were further investigated in continuous adsorption mode for the possible scale-up studies. The effect of flow rate, bed-height and inlet ion concentration on the adsorption characteristics were investigated in a fixed-bed adsorber. The isotherm data of continuous adsorption were best fitted to the Langmuir isotherm model, while the breakthrough data were found to be in good agreement with the Yoon-Nelson models for all experimental conditions used. The adsorbent regeneration results indicated a good adsorption-desorption process reversibility in both batch and continuous system. The process design of the fixed-bed adsorber was successfully demonstrated by using the height of an equivalent transfer unit and empty bed contact time analysis to predict the breakthrough curves of the scale-up adsorber. The adsorption efficiency of the adsorbent was also evaluated by measuring the extent of adsorption of mercury in oil-field produced water. The use of rice residues to remove mercury leads to the production of a highly effective adsorbent generated from less expensive raw materials from renewable resources
Description
Thesis (PhD. (Chemical Engineering))
Keywords
Adsorption—Materials, Sewage—Purification—Heavy metals removal, Mercury compounds—Environmental aspects