{"id":{"repo_id":"unr","oai_identifier":"oai:scholarwolf.unr.edu:11714/11956"},"canonical_url":"https://search.dev.ndltd.org/etd/unr/oai:scholarwolf.unr.edu:11714/11956","repository":{"repo_id":"unr","name":"University of Nevada - Reno","base_url":"https://scholarwolf.unr.edu/server/oai/request"},"display":{"title":"Hydrometallurgical processing of nickel sulfides with activated carbon in sulfuric acid medium","abstract":"The growing global transition toward low‑carbon energy systems and electrification technologies has resulted inunprecedented demand for nickel and associated critical metals such as copper, cobalt, manganese, and chromium. Though primary mining remains the dominant supply pathway, increasing scrutiny of environmental impacts, declining ore grades, and resource inefficiencies have intensified interest in secondary metal sources. Conversely, among these, sulfide‑rich mine flotation tailings are of particular significance, as they represent both a long‑term environmental liability and a potentially valuable repository of unrecovered metals. This dissertation investigates nickel sulfide flotation tailings as a coupled environmental-metallurgical system by integrating geochemical characterization, acid mine drainage assessment, leachability studies (with oxidants, organic and inorganic acids), as well as redox‑controlled hydrometallurgical processing using activated carbon to enable sustainable metal recovery. The research begins with a comprehensive characterization of rougher, cleaner, and thickener tailings generated froma nickel sulfide processing circuit. Here, acid-base accounting, mineralogical analysis, and sequential extraction procedures were employed to evaluate metal speciation, mobility, and acid mine drainage potential. The results indicate that the majority of nickel and associated metals are strongly bound within sulfide and silicate phases, suggesting limited short‑term environmental mobility but substantial recoverability under appropriate chemical conditions. The findings from acid-base accounting further revealed that cleaner tailings pose a heightened risk of acid mine drainage generation due to depletion of reactive carbonates and Mg‑silicates responsible for acid neutralization during sulfide oxidation. These findings ultimately underscore the importance of integrating environmental risk assessment with resource recovery strategies when managing sulfide tailings, especially with high sulfur content. Building on this geochemical foundation, the hydrometallurgical potential of the tailings was investigated throughsystematic leaching studies using inorganic acids, organic ligands, and oxidizing agents. The initial leaching experiments established that effective metal dissolution requires strongly acidic and oxidative environments. Sulfuric acid was selected as the principal lixiviant due to its industrial relevance, while ferric ions were identified as a critical oxidant facilitating sulfide mineral breakdown. Sequential extraction and batch leaching experiments demonstrated that more than 90% of base metals can be recovered from tailings under optimized acidic and oxidative conditions. Further, advanced process optimization was achieved using response surface methodology to quantify the interactive effects of sulfuric acid concentration, ferric chloride dosage, chelating agents, temperature, and leaching time on the simultaneous recovery of nickel, copper, cobalt, chromium, and manganese from the polymetallic tailings. Statistical analysis revealed ferric ion concentration as the most influential parameter controlling the dissolution ofnickel, copper, cobalt, and manganese, while chromium recovery was more sensitive to temperature and acid strength. Under optimized conditions, optimal nickel and copper recoveries together with the extraction of other critical metals was achieved. The findings show the technical feasibility of tailings reprocessing to supplement metal supply pathways. To further intensify oxidative leaching, chloride salts and activated carbon were introduced as catalytic and redox‑mediating agents. The introduction of ferric chloride significantly enhanced sulfide oxidation kinetics, while activated carbon was shown to catalyze iron redox cycling by promoting the regeneration of ferric ions from ferrous species in solution. This mechanism sustained high oxidation-reduction potentials and accelerated sulfide dissolution across materials of varying grade, liberation, and gangue content, including both flotation tailings and primary sulfideconcentrates. Importantly, the granular activated carbon demonstrated reusability without significant loss of performance. This property indicates improves the economic and environmental viability of the proposed approach. Kinetic analyses across multiple leaching systems were interpreted using shrinking‑core models. The computations revealed that metal dissolution is governed by a combination of chemically controlled and diffusion‑controlled mechanisms depending on mineralogy, oxidant availability, and reaction conditions. The apparent activation energies derived from Arrhenius relationships were consistent with redox‑driven sulfide oxidation and internal diffusion through product layers. These kinetic insights provide a mechanistic basis for process scale‑up and design. Overall, this dissertation establishes an integrated framework for transforming nickel sulfide flotation tailings from environmentally problematic waste into valuable secondary resources. By coupling the geochemistry, redox chemistry, and leaching kinetics, the research advances sustainable tailings management and contributes to circular economy strategies aimed at securing critical metal supply whereas reducing the ecological footprint of such mining operations.","abstract_html":"The growing global transition toward low‑carbon energy systems and electrification technologies has resulted inunprecedented demand for nickel and associated critical metals such as copper, cobalt, manganese, and chromium. Though primary mining remains the dominant supply pathway, increasing scrutiny of environmental impacts, declining ore grades, and resource inefficiencies have intensified interest in secondary metal sources. Conversely, among these, sulfide‑rich mine flotation tailings are of particular significance, as they represent both a long‑term environmental liability and a potentially valuable repository of unrecovered metals. This dissertation investigates nickel sulfide flotation tailings as a coupled environmental-metallurgical system by integrating geochemical characterization, acid mine drainage assessment, leachability studies (with oxidants, organic and inorganic acids), as well as redox‑controlled hydrometallurgical processing using activated carbon to enable sustainable metal recovery. The research begins with a comprehensive characterization of rougher, cleaner, and thickener tailings generated froma nickel sulfide processing circuit. Here, acid-base accounting, mineralogical analysis, and sequential extraction procedures were employed to evaluate metal speciation, mobility, and acid mine drainage potential. The results indicate that the majority of nickel and associated metals are strongly bound within sulfide and silicate phases, suggesting limited short‑term environmental mobility but substantial recoverability under appropriate chemical conditions. The findings from acid-base accounting further revealed that cleaner tailings pose a heightened risk of acid mine drainage generation due to depletion of reactive carbonates and Mg‑silicates responsible for acid neutralization during sulfide oxidation. These findings ultimately underscore the importance of integrating environmental risk assessment with resource recovery strategies when managing sulfide tailings, especially with high sulfur content. Building on this geochemical foundation, the hydrometallurgical potential of the tailings was investigated throughsystematic leaching studies using inorganic acids, organic ligands, and oxidizing agents. The initial leaching experiments established that effective metal dissolution requires strongly acidic and oxidative environments. Sulfuric acid was selected as the principal lixiviant due to its industrial relevance, while ferric ions were identified as a critical oxidant facilitating sulfide mineral breakdown. Sequential extraction and batch leaching experiments demonstrated that more than 90% of base metals can be recovered from tailings under optimized acidic and oxidative conditions. Further, advanced process optimization was achieved using response surface methodology to quantify the interactive effects of sulfuric acid concentration, ferric chloride dosage, chelating agents, temperature, and leaching time on the simultaneous recovery of nickel, copper, cobalt, chromium, and manganese from the polymetallic tailings. Statistical analysis revealed ferric ion concentration as the most influential parameter controlling the dissolution ofnickel, copper, cobalt, and manganese, while chromium recovery was more sensitive to temperature and acid strength. Under optimized conditions, optimal nickel and copper recoveries together with the extraction of other critical metals was achieved. The findings show the technical feasibility of tailings reprocessing to supplement metal supply pathways. To further intensify oxidative leaching, chloride salts and activated carbon were introduced as catalytic and redox‑mediating agents. The introduction of ferric chloride significantly enhanced sulfide oxidation kinetics, while activated carbon was shown to catalyze iron redox cycling by promoting the regeneration of ferric ions from ferrous species in solution. This mechanism sustained high oxidation-reduction potentials and accelerated sulfide dissolution across materials of varying grade, liberation, and gangue content, including both flotation tailings and primary sulfideconcentrates. Importantly, the granular activated carbon demonstrated reusability without significant loss of performance. This property indicates improves the economic and environmental viability of the proposed approach. Kinetic analyses across multiple leaching systems were interpreted using shrinking‑core models. The computations revealed that metal dissolution is governed by a combination of chemically controlled and diffusion‑controlled mechanisms depending on mineralogy, oxidant availability, and reaction conditions. The apparent activation energies derived from Arrhenius relationships were consistent with redox‑driven sulfide oxidation and internal diffusion through product layers. These kinetic insights provide a mechanistic basis for process scale‑up and design. Overall, this dissertation establishes an integrated framework for transforming nickel sulfide flotation tailings from environmentally problematic waste into valuable secondary resources. By coupling the geochemistry, redox chemistry, and leaching kinetics, the research advances sustainable tailings management and contributes to circular economy strategies aimed at securing critical metal supply whereas reducing the ecological footprint of such mining operations.","abstract_has_math":false,"creators":["Mends, Emmanuel Atta"],"institution":null,"degree_name":null,"degree_level":"Doctorate Degree","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Chu, Pengbo"],"committee_chairs":[],"committee_members":["Pan, Lei","Vahidi, Eshan","Nesbitt, Carl C","Yang, Yu"],"year":2026,"date_issued":"2026","date_published":"2026","updated_at":"2026-07-27T21:45:45Z","subjects":["activated carbon","copper","leaching","nickel","sulfuric acid","tailings"],"languages":["en_US","English"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://scholarwolf.unr.edu/handle/11714/11956","outbound_label":"Repository record","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Chu, Pengbo"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Pan, Lei","Vahidi, Eshan","Nesbitt, Carl C","Yang, Yu"]},{"key":"dc:creator","label":"Author","values":["Mends, Emmanuel Atta"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["01/01/2026"]},{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-06-25T16:43:41Z"]},{"key":"dc:date.issued","label":"Date","values":["2026"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Doctorate Degree"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["activated carbon","copper","leaching","nickel","sulfuric acid","tailings"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English"]},{"key":"dc:language.iso","label":"Language (ISO)","values":["en_US"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://scholarwolf.unr.edu/handle/11714/11956"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The growing global transition toward low‑carbon energy systems and electrification technologies has resulted inunprecedented demand for nickel and associated critical metals such as copper, cobalt, manganese, and chromium. Though primary mining remains the dominant supply pathway, increasing scrutiny of environmental impacts, declining ore grades, and resource inefficiencies have intensified interest in secondary metal sources. Conversely, among these, sulfide‑rich mine flotation tailings are of particular significance, as they represent both a long‑term environmental liability and a potentially valuable repository of unrecovered metals. This dissertation investigates nickel sulfide flotation tailings as a coupled environmental-metallurgical system by integrating geochemical characterization, acid mine drainage assessment, leachability studies (with oxidants, organic and inorganic acids), as well as redox‑controlled hydrometallurgical processing using activated carbon to enable sustainable metal recovery. The research begins with a comprehensive characterization of rougher, cleaner, and thickener tailings generated froma nickel sulfide processing circuit. Here, acid-base accounting, mineralogical analysis, and sequential extraction procedures were employed to evaluate metal speciation, mobility, and acid mine drainage potential. The results indicate that the majority of nickel and associated metals are strongly bound within sulfide and silicate phases, suggesting limited short‑term environmental mobility but substantial recoverability under appropriate chemical conditions. The findings from acid-base accounting further revealed that cleaner tailings pose a heightened risk of acid mine drainage generation due to depletion of reactive carbonates and Mg‑silicates responsible for acid neutralization during sulfide oxidation. These findings ultimately underscore the importance of integrating environmental risk assessment with resource recovery strategies when managing sulfide tailings, especially with high sulfur content. Building on this geochemical foundation, the hydrometallurgical potential of the tailings was investigated throughsystematic leaching studies using inorganic acids, organic ligands, and oxidizing agents. The initial leaching experiments established that effective metal dissolution requires strongly acidic and oxidative environments. Sulfuric acid was selected as the principal lixiviant due to its industrial relevance, while ferric ions were identified as a critical oxidant facilitating sulfide mineral breakdown. Sequential extraction and batch leaching experiments demonstrated that more than 90% of base metals can be recovered from tailings under optimized acidic and oxidative conditions. Further, advanced process optimization was achieved using response surface methodology to quantify the interactive effects of sulfuric acid concentration, ferric chloride dosage, chelating agents, temperature, and leaching time on the simultaneous recovery of nickel, copper, cobalt, chromium, and manganese from the polymetallic tailings. Statistical analysis revealed ferric ion concentration as the most influential parameter controlling the dissolution ofnickel, copper, cobalt, and manganese, while chromium recovery was more sensitive to temperature and acid strength. Under optimized conditions, optimal nickel and copper recoveries together with the extraction of other critical metals was achieved. The findings show the technical feasibility of tailings reprocessing to supplement metal supply pathways. To further intensify oxidative leaching, chloride salts and activated carbon were introduced as catalytic and redox‑mediating agents. The introduction of ferric chloride significantly enhanced sulfide oxidation kinetics, while activated carbon was shown to catalyze iron redox cycling by promoting the regeneration of ferric ions from ferrous species in solution. This mechanism sustained high oxidation-reduction potentials and accelerated sulfide dissolution across materials of varying grade, liberation, and gangue content, including both flotation tailings and primary sulfideconcentrates. Importantly, the granular activated carbon demonstrated reusability without significant loss of performance. This property indicates improves the economic and environmental viability of the proposed approach. Kinetic analyses across multiple leaching systems were interpreted using shrinking‑core models. The computations revealed that metal dissolution is governed by a combination of chemically controlled and diffusion‑controlled mechanisms depending on mineralogy, oxidant availability, and reaction conditions. The apparent activation energies derived from Arrhenius relationships were consistent with redox‑driven sulfide oxidation and internal diffusion through product layers. These kinetic insights provide a mechanistic basis for process scale‑up and design. Overall, this dissertation establishes an integrated framework for transforming nickel sulfide flotation tailings from environmentally problematic waste into valuable secondary resources. By coupling the geochemistry, redox chemistry, and leaching kinetics, the research advances sustainable tailings management and contributes to circular economy strategies aimed at securing critical metal supply whereas reducing the ecological footprint of such mining operations."]},{"key":"dc:format","label":"Dc Format","values":["PDF"]},{"key":"dc:title","label":"Title","values":["Hydrometallurgical processing of nickel sulfides with activated carbon in sulfuric acid medium"]}]}],"canonical_facts":{"dc:contributor.advisor":["Chu, Pengbo"],"dc:contributor.committeemember":["Pan, Lei","Vahidi, Eshan","Nesbitt, Carl C","Yang, Yu"],"dc:creator":["Mends, Emmanuel Atta"],"dc:date":["01/01/2026"],"dc:date.accessioned":["2026-06-25T16:43:41Z"],"dc:date.issued":["2026"],"dc:description.abstract":["The growing global transition toward low‑carbon energy systems and electrification technologies has resulted inunprecedented demand for nickel and associated critical metals such as copper, cobalt, manganese, and chromium. Though primary mining remains the dominant supply pathway, increasing scrutiny of environmental impacts, declining ore grades, and resource inefficiencies have intensified interest in secondary metal sources. Conversely, among these, sulfide‑rich mine flotation tailings are of particular significance, as they represent both a long‑term environmental liability and a potentially valuable repository of unrecovered metals. This dissertation investigates nickel sulfide flotation tailings as a coupled environmental-metallurgical system by integrating geochemical characterization, acid mine drainage assessment, leachability studies (with oxidants, organic and inorganic acids), as well as redox‑controlled hydrometallurgical processing using activated carbon to enable sustainable metal recovery. The research begins with a comprehensive characterization of rougher, cleaner, and thickener tailings generated froma nickel sulfide processing circuit. Here, acid-base accounting, mineralogical analysis, and sequential extraction procedures were employed to evaluate metal speciation, mobility, and acid mine drainage potential. The results indicate that the majority of nickel and associated metals are strongly bound within sulfide and silicate phases, suggesting limited short‑term environmental mobility but substantial recoverability under appropriate chemical conditions. The findings from acid-base accounting further revealed that cleaner tailings pose a heightened risk of acid mine drainage generation due to depletion of reactive carbonates and Mg‑silicates responsible for acid neutralization during sulfide oxidation. These findings ultimately underscore the importance of integrating environmental risk assessment with resource recovery strategies when managing sulfide tailings, especially with high sulfur content. Building on this geochemical foundation, the hydrometallurgical potential of the tailings was investigated throughsystematic leaching studies using inorganic acids, organic ligands, and oxidizing agents. The initial leaching experiments established that effective metal dissolution requires strongly acidic and oxidative environments. Sulfuric acid was selected as the principal lixiviant due to its industrial relevance, while ferric ions were identified as a critical oxidant facilitating sulfide mineral breakdown. Sequential extraction and batch leaching experiments demonstrated that more than 90% of base metals can be recovered from tailings under optimized acidic and oxidative conditions. Further, advanced process optimization was achieved using response surface methodology to quantify the interactive effects of sulfuric acid concentration, ferric chloride dosage, chelating agents, temperature, and leaching time on the simultaneous recovery of nickel, copper, cobalt, chromium, and manganese from the polymetallic tailings. Statistical analysis revealed ferric ion concentration as the most influential parameter controlling the dissolution ofnickel, copper, cobalt, and manganese, while chromium recovery was more sensitive to temperature and acid strength. Under optimized conditions, optimal nickel and copper recoveries together with the extraction of other critical metals was achieved. The findings show the technical feasibility of tailings reprocessing to supplement metal supply pathways. To further intensify oxidative leaching, chloride salts and activated carbon were introduced as catalytic and redox‑mediating agents. The introduction of ferric chloride significantly enhanced sulfide oxidation kinetics, while activated carbon was shown to catalyze iron redox cycling by promoting the regeneration of ferric ions from ferrous species in solution. This mechanism sustained high oxidation-reduction potentials and accelerated sulfide dissolution across materials of varying grade, liberation, and gangue content, including both flotation tailings and primary sulfideconcentrates. Importantly, the granular activated carbon demonstrated reusability without significant loss of performance. This property indicates improves the economic and environmental viability of the proposed approach. Kinetic analyses across multiple leaching systems were interpreted using shrinking‑core models. The computations revealed that metal dissolution is governed by a combination of chemically controlled and diffusion‑controlled mechanisms depending on mineralogy, oxidant availability, and reaction conditions. The apparent activation energies derived from Arrhenius relationships were consistent with redox‑driven sulfide oxidation and internal diffusion through product layers. These kinetic insights provide a mechanistic basis for process scale‑up and design. Overall, this dissertation establishes an integrated framework for transforming nickel sulfide flotation tailings from environmentally problematic waste into valuable secondary resources. By coupling the geochemistry, redox chemistry, and leaching kinetics, the research advances sustainable tailings management and contributes to circular economy strategies aimed at securing critical metal supply whereas reducing the ecological footprint of such mining operations."],"dc:format":["PDF"],"dc:identifier.uri":["https://scholarwolf.unr.edu/handle/11714/11956"],"dc:language":["English"],"dc:language.iso":["en_US"],"dc:subject":["activated carbon","copper","leaching","nickel","sulfuric acid","tailings"],"dc:title":["Hydrometallurgical processing of nickel sulfides with activated carbon in sulfuric acid medium"],"dc:type":["Dissertation"],"thesis:degree_level":["Doctorate Degree"]},"updated_at":"2026-07-27T21:45:45Z"}