Studies On Hazard-free Treatment And Comprehensive Utilisation Of Iron Residues Containing Arsenic Released From Nickel Hydrometallurgy Process

This thesis study on hazard-free treatment and precious metals enrichment of iron residues which are discarded by the hydrometallurgical industrial processes is recognized as a hazardous waste due to its high concentration of arsenic and heavy metals.The details are as follows:The leaching solution was obtained from hazardous iron residues by selective acid-leaching process.In addition,the solution which treated by arsenic removal,precious metals enrichment and crude separation of copper?cobalt?nickel can be recycled to nickel anodic electrolyte production line,and the high purity nickel cathode electrolyte was obtained after further purification.The XPS analysis revealed that arsenic in the iron residues was present in the form of As???.H₂O₂ was chosen to oxidize As???to As?V?,and the pH was accurately controlled,then As?V?co-precipitation with Fe???and 99.9% arsenic was precipitated as FeAsO₄.The best arsenic removal was under the condition that the amount of hydrogen peroxide was 1.36 times the molar amount of As???and the solution pH was adjusted to 2.8-3.0.The FeAs O₄ was confirmed by XRD and XPS.In order to reduce the pressure of the introduction of the leaching solution into the nickel anodic electrolyte system.97% copper was removed under the condition that the solution pH was adjusted to 3.8-4.0 by NaHCO₃ at 30 oC for 8 h.In addition,the mole ratio of Cu/Ni in the Cu-removal precipitates exceeded 30.The copper content in filter solution was below 1 g/L which coincided with the nickel anodic electrolyte produced by system.The emerald residue obtained from Cu removal process was characterized by XRD?SEM and FI-IR,and the precipitate was Cu₂?OH?₂CO₃.The precipitate can be directly used in the production of electrolytic copper by acid dissolving.The cobalt in the leaching solution can be removed as Co?OH?₃ by NaClO or K₂S₂O₈ and the cobalt removal rate was 99.9%.Enrichment and selective separation of trace precious metals from complex nickel electrolysis system by two polymeric N-methyl imidazole ionic liquids with hydrophobicity.High recovery rate of precious metals can be achieved by these two ionic liquids within 5 h.Temperature had no obvious influence on sorption,25 oC was the best.Based on the experimental results,Au???sorption is along with a physicochemical sorption process since the adsorption followed second-order kinetic model and Freundlich adsorption isotherm.In addition,the adsorbent was also exhibited high Au???ion selectivity and the selectivity coefficient of Au???relative to Cu?II?,Ni?II?were very high.Moreover,thiourea was used in the elution of Au???and ionic liquid can be regenerated,which enhances the economic benefits for the practical application.The non-hazardous Na-jarosite produced by selective acid-leaching process was investigated by thermal analysis.The sodium jarosite only loss of adsorbed water in the range of 30-300 oC.From 300 to 404.4 oC,the jarosite structure is broken down and form NaFe?SO₄?₂ and hematite.NaFe?SO₄?₂ decomposes to form Fe₂O₃ and Na₂SO₄ in the range of 579.4-695.6 oC.In order to verify the reaction and the sample composition under these temperature ranges,the calcined samples under 274 oC,480 oC,580 oC,698 oC,800 oC were characterized by XRD analysis,then washing the samples and measure the pH of water washing filtrate.According to SEM analysis,the Fe₂O₃ has random shape.Given comprehensive consideration,the optimum calcination temperature was chosen at 698 oC.The calcined samples after washing could be used as pigments.The ordinary solid waste received comprehensive utilisation.