Utilization Of Natrojarosite Slag From Nickel Electrolysis

Natrojarosite slag is mainly from industrial electrolyte removing ferric ion,smuggling a few of non-ferrous elements,elements scattered elements and precious metal elements.Recycling of valuable elements to produce high value-added products is the way to comprehensive utilization of industrial slag and protection of natural resources and the environment.Using the slag from a company of nickel electrolysis as raw material,the methods of comprehensive recovery of iron,zinc,nickel,copper,precious metals in the slag are explored in the paper.Through the analysis of structure and chemical composition of the natrojarosite slag,the slag mainly contains the natrojarosite,barium sulfate and lead sulfate,a small amount of tellurite,copper sulfate and nickel sulfate,and trace amounts of precious metal.The element contents such as iron,sodium,barium,lead,tellurium,copper and nickel are 28.3%,4.2%,6.0%,4.2%,0.24%,0.8%and 0.6%.Iron and sodium exist in crystal structure of the natrojarosite.Barium and lead elements are in the slag with the form of barium sulfate and lead sulfate.Copper and nickel are most soluble sulfates entrained in the slag.Tellurium element is present in the slag with soluble tellurates.According to the characteristics of the structure and chemical composition of natrojarosite slag,the slag can be decomposed by sulfuric acid,turn to filtrate and filtration residue through filtration in this paper.The filtrate contains elements,such as iron,tellurium,copper and nickel.Methyl isobutyl ketone can be used to extract iron and tellurium,and the extracted iron turn to iron oxide red.LⅨ984 extraction of copper,nickel P204 extraction.The precious metals in the residue can be leached by aqua regia.Preparation of iron oxide:iron in the filtrate is extracted by methyl isobutyl ketone（MIBK）to prepare iron oxide.The solution is added concentrated hydrochloric acid and sodium chloride solids,after tetravalent tellurium is oxidized to hexavalent tellurium by hydrogen peroxide.Ferric ion is extraced by ethyl isobutyl ketone about 2min,in the 6 mol L^-1 hydrochloric acid medium,with the volume ratio of organic phase and extractant phase（1:1）,and its extraction ratio reachs 95%.Three-stage countercurrent extraction-back extraction,the ferric concentration in stripping solution is about 80 g L^-1.and this solution does not contain impurity elements.The ferric ion is reduced to ferrous ion by scrap metal skin（chips）.Tartaric acid as a dispersing agent,sodium dodecyl benzene sulfonate as a surfactant,ammonia-sodium bicarbonate solution is slowly dropped FeCl₂ solution,with constant stirring to form a precipitate.The precipitation of ferrous carbonate after washing and drying is calcined to prepare the product of ferric oxide about 1.5 h at 600 ^oC.The results show that the product has the crystal structure of Fe₂O₃ with X-ray diffraction analysis,and its content is over92.4%.Its diffraction peak intensity is high,half width is narrowed and its crystal is finer complete.Contain small amounts FeFe₂O₄,Fe₅Al₄Si₆O₂₂（OH）₂ and other miscellaneous phase.Compared with standard HO_01-04 and H130 of iron oxide,the product meets the secondary standard.Recovery of tellurium:the raffinate after extraction of iron is concentrated by heating,to crystallize sodium sulfate,to recover hydrochloric acid,while tellurium is reduced to Te（Ⅳ）,and then Te（Ⅳ）is extracted with methyl isobutyl ketone.Under the conditions of 6 mol L^-11 of hydrochloric acid,phase ratio（O/A）about 1:1,at 2 min,the extraction rate of tellurium element is over 90%.It is difficult to separate the organic and aqueous phases in the back-extraction process because of emulsification,impurities goes into the stripping solution.The stripping solution with adding 2%hydrochloric acid can avoid emulsification.Recovery of copper and nickel:the raffinate after tellurium extracted is evaporated to recovery hydrochloric acid,and then sulfuric acid dissolves crystalline solid.In the sulfuric acid medium,LⅨ984 extracts copper and P204 extracts nickel.Using as extractant 20%LⅨ984 in sulfonated kerosene,copper could be selectively extracted in the organic phase,while nickel remained in the aqueous phase.Experimental conditions,including the pH of the extracted solution（2.5）,the ratio of aqueous to organic phase（1:1）and the contact time（2 min）are accepted,and the extraction rate of copper is 92%.Its back-extraction ratio is 99%under the conditions of 4 mol L^-1sulfuric acid and phase ratio（1:1）.Adjusting pH to 5.5 in the raffinate after copper extracted,Nickel extraction rate is more than 98%by 30%P204 in sulfonated kerosene under the conditions of the ratio of aqueous to organic phase（1:1）and at 2 min.Recovery of precious metals:X-ray diffraction analysis shows that the residue contains hokutolite（（Ba,Pb）SO₄）and a small amount of effenbergerit(BaCuSi₄O₁₀),after the natrojarosite slag is broken down by concentrated sulfuric acid.Subsequently,the methods for leaching precious metals in the filtration are explored with ammonium thiocyanate（non-cyanide）,aqua regia and hydrochloric acid.At pH=10,adding 0.2%of NH4SCN solution,leaching with stirring at 38 h,the leaching rate of the precious metals in the residue is less than 5.5%.The leaching rates of the precious metals are more than 95%with aqua regia（25%）at 8 h.This method can simultaneously recover precious metals and have short cycle,but require equipment.The method of leaching precious metals by hydrochloric acid（25%）can reduce equipment costs,but the recoveries of precious metals are less than 50%.It is simple for the process including recovery of valuable elements to produce high value-added ferric oxide,recycle of hydrochloric acid and the extraction agent to obtain significant economic benefits,while reduce environmental pressures,and it is also important at the aspect of environmental geochemistry research.