All over the world, agro-food residues are constantly generated and disposed of without much value-addition. The disposals of these agro-wastes tend to pose environmental threats to inhabitants. Besides, heavy industrial activities such as mining, hydrometallurgy and pigmentation have brought about ...
All over the world, agro-food residues are constantly generated and disposed of without much value-addition. The disposals of these agro-wastes tend to pose environmental threats to inhabitants. Besides, heavy industrial activities such as mining, hydrometallurgy and pigmentation have brought about releases of toxic metals and dyes into the aquatic environments. Conventional gold mining particularly involves carbon adsorption stage in industrial carbon-in-pulp (CIP) and carbon-in-leach (CIL) plants. However, the over-reliance of imported and expensive activated carbons (ACs) from overseas raises the overall operational cost, especially for developing countries like Ghana. Thus for sustainable development, agro-wastes including fruit peels should be converted into valuable products that will be beneficial to humans and their environments. In this dissertation therefore, ACs were synthesized from agro-waste precursors via modifications with various activation agents, in a bid to produce cheaper alternative carbons for applications in mining and industrial wastewater treatments.
In chapter 3, precursor-based ACs were first synthesized from agro-waste precursors including the peels of orange, mango, cassava, plantain, pineapple, banana, cocoyam, coir dust, snails, palm fiber, palm kernel and cocoa pod husk, via KOH-activation. Next, the orange peel which recorded the best aurocyanide adsorption capacity from an initial evaluation was selected to synthesize activation-agent based ACs using H2SO4, H3PO4, ZnCl2, KOH NaOH as the activation agents. The physicochemical characteristics, adsorption behaviors and mechanisms were studied via detailed instrumental characterization using FTIR, XRD, BET, DSC/TGA and XPS equipment. The physicochemical changes were more significant in the activation agent-based carbons than the precursor-based carbons owing to the different degrees of reactivities. The ZnCl2-AC and KOH-AC were the best in terms of adsorption capacities, with experimental uptakes reaching 346.34 and 327.88 mg/g, respectively, which were higher than those of commercial ACs, Haycarb and Norit C-Gran. The presence of micro and mesopores, coupled with the combined effects of electrostatic binding, π‒π (pi-pi) interactions and ion-pair formations, influenced the significantly high adsorption capacities obtained.
In chapter 4, amine-functionalized carbons were prepared by post-synthesis modification of KOH-activated carbon with the quaternary ammonium moiety, (3-Chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC). A significant improvement in the aurocyanide adsorption capacity was obtained, with an estimated equilibrium uptake reaching 749.28 34.79 mg/g, according to the Langmuir isotherm model. Next in chapter 5, adsorptive treatments of heavy metal-laden mine wastewaters were studied. Simulated acid mine drainage (AMD) solutions containing As, Hg, Pb, Cd, Cu and Co were examined. The ZnCl2-AC recorded the highest adsorption capacity of 526.3150.52 mg/g for Hg(II), and the overall order of adsorption capacity was ZnCl2-AC for Hg(II) > KOH-AC for Pb(II) > NaOH-AC for Cd(II) > NaOH-AC for Co(II) > NaOH-AC for Cu(II) > ZnCl2-AC for As(V).
For potential applications in urban mining, the activation agent-based carbons were applied for recovery of gold from simulated chloride-reach acidic leach wastewaters in chapter 6. The H2SO4-AC showed the highest gold uptake of 1679.7437.66 mg/g, which was aided by ion exchange and adsorption-reduction mechanisms. Finally, chapter 7 focused on dye wastewater treatment using the synthesized materials. The KOH-AC and ZnCl2-AC exhibited the highest Methylene blue adsorption capacities from simulated and laboratory organic wastewater samples. The adsorption mechanisms were elucidated as involving intra-particle diffusions, electrostatic and π‒π interaction interactions, hydrogen bond formations and electron donor-acceptor reactions.
All over the world, agro-food residues are constantly generated and disposed of without much value-addition. The disposals of these agro-wastes tend to pose environmental threats to inhabitants. Besides, heavy industrial activities such as mining, hydrometallurgy and pigmentation have brought about releases of toxic metals and dyes into the aquatic environments. Conventional gold mining particularly involves carbon adsorption stage in industrial carbon-in-pulp (CIP) and carbon-in-leach (CIL) plants. However, the over-reliance of imported and expensive activated carbons (ACs) from overseas raises the overall operational cost, especially for developing countries like Ghana. Thus for sustainable development, agro-wastes including fruit peels should be converted into valuable products that will be beneficial to humans and their environments. In this dissertation therefore, ACs were synthesized from agro-waste precursors via modifications with various activation agents, in a bid to produce cheaper alternative carbons for applications in mining and industrial wastewater treatments.
In chapter 3, precursor-based ACs were first synthesized from agro-waste precursors including the peels of orange, mango, cassava, plantain, pineapple, banana, cocoyam, coir dust, snails, palm fiber, palm kernel and cocoa pod husk, via KOH-activation. Next, the orange peel which recorded the best aurocyanide adsorption capacity from an initial evaluation was selected to synthesize activation-agent based ACs using H2SO4, H3PO4, ZnCl2, KOH NaOH as the activation agents. The physicochemical characteristics, adsorption behaviors and mechanisms were studied via detailed instrumental characterization using FTIR, XRD, BET, DSC/TGA and XPS equipment. The physicochemical changes were more significant in the activation agent-based carbons than the precursor-based carbons owing to the different degrees of reactivities. The ZnCl2-AC and KOH-AC were the best in terms of adsorption capacities, with experimental uptakes reaching 346.34 and 327.88 mg/g, respectively, which were higher than those of commercial ACs, Haycarb and Norit C-Gran. The presence of micro and mesopores, coupled with the combined effects of electrostatic binding, π‒π (pi-pi) interactions and ion-pair formations, influenced the significantly high adsorption capacities obtained.
In chapter 4, amine-functionalized carbons were prepared by post-synthesis modification of KOH-activated carbon with the quaternary ammonium moiety, (3-Chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC). A significant improvement in the aurocyanide adsorption capacity was obtained, with an estimated equilibrium uptake reaching 749.28 34.79 mg/g, according to the Langmuir isotherm model. Next in chapter 5, adsorptive treatments of heavy metal-laden mine wastewaters were studied. Simulated acid mine drainage (AMD) solutions containing As, Hg, Pb, Cd, Cu and Co were examined. The ZnCl2-AC recorded the highest adsorption capacity of 526.3150.52 mg/g for Hg(II), and the overall order of adsorption capacity was ZnCl2-AC for Hg(II) > KOH-AC for Pb(II) > NaOH-AC for Cd(II) > NaOH-AC for Co(II) > NaOH-AC for Cu(II) > ZnCl2-AC for As(V).
For potential applications in urban mining, the activation agent-based carbons were applied for recovery of gold from simulated chloride-reach acidic leach wastewaters in chapter 6. The H2SO4-AC showed the highest gold uptake of 1679.7437.66 mg/g, which was aided by ion exchange and adsorption-reduction mechanisms. Finally, chapter 7 focused on dye wastewater treatment using the synthesized materials. The KOH-AC and ZnCl2-AC exhibited the highest Methylene blue adsorption capacities from simulated and laboratory organic wastewater samples. The adsorption mechanisms were elucidated as involving intra-particle diffusions, electrostatic and π‒π interaction interactions, hydrogen bond formations and electron donor-acceptor reactions.
주제어
#Agro-waste Activated carbon Physicochemical properties Aurocyanide Wastewater treatment Adsorption
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