Detoxification And Recovery Of Chromium In Chromium-containing Metallurgical Solid Waste

The metallurgical industry occupies a very important position in my country’s national economy and supports the healthy and stable development of my country’s manufacturing industry.With the rapid development of the metallurgical industry,a large amount of harmful solid waste has also been generated,and the waste residue containing heavy metals will cause serious harm to the environment and human health.The detoxification and resource utilization of chromium in chromium-containing metallurgical solid waste is a problem that both environmental protection and metallurgical industries are very concerned about.This paper takes stainless steel slag as the research object,and designs different high-temperature solid-phase reactions to carry out the extraction and recovery experiment of chromium in stainless steel slag and the reduction and detoxification experiment of Cr（Ⅵ）.Through composition analysis,phase analysis,comprehensive thermal analysis,infrared analysis,photoelectron spectroscopy analysis,electron microscopic analysis and chemical theoretical calculation,the occurrence state of chromium in stainless steel slag,the differences in the reduction products of Cr（Ⅵ）by different solid carbon powders,the reaction mechanism of carbothermal reduction of Cr（Ⅵ）and sulfide reduction of Cr（Ⅵ）was studied.And explored new ways and methods for the recovery,detoxification and resource utilization of chromium in stainless steel slag.The following conclusions were reached:（1）The the content of chromium（in the form of Cr₂O₃）in the stainless steel slag of Taiyuan Iron and Steel Co.,Ltd.is 6.03%,mainly in the form of chromium-magnesium spinel and chromium-manganese sulfide solid solution.（2）The high-temperature oxidative roasting method with the addition of sodiumizing agent can realize the efficient recovery of chromium in stainless steel slag.Using the mixture of Na₂CO₃ and Na OH as the sodiumizing agent and Na Al O₂ as the fixing agent,dry grinding and activating the stainless steel slag,roasting the mixture of the above substances at 900℃for 2 h,the recovery rate of chromium is reaching96.83%.（3）Different types of solid carbon powders have different types and quantities of organic functional groups on the surface of the toners,resulting in different oxygen activities of the carbon powders.The onset temperature leading to carbothermal reduction of Cr（Ⅵ）to Cr₃C₂ varies due to the different reactivity of different types of solid carbon powders.Nano carbon powder only contains C-C single bond,and has the highest activity,and the initial temperature of Cr₃C₂ is the lowest,which is 800℃.The coke contains C=O and O-H bonds,the activity is the lowest,and the initial temperature of Cr₃C₂ is the highest,reaching 1200℃.（4）In a reducing atmosphere and a temperature of 1200℃,the carbothermal reduction reaction has gone through the following processes:carbon powders and Cr O₃eutectic melt into an amorphous mixture→carbon powder and Cr O₃ react to form Cr₂O₃ crystals→carbon powder is wrapped in Cr₂O₃ crystals,Cr₃C₂ crystals are formed on the surface of Cr₂O₃ crystals to form"carbon powder-Cr₃C₂-Cr₂O₃"three-layer crystal particles→In the three-layer crystal particles,the particle size of Cr₂O₃in the inner layer gradually becomes smaller,the Cr₃C₂ in the middle layer gradually becomes larger,and the carbon coating in the outer layer gradually becomes larger.The cladding gradually becomes thinner.（5）In the high-temperature reduction of Cr（Ⅵ）by Zn S and Cu S,Zn S can reduce Cr（Ⅵ）to form Zn Cr₂O₄ at 700℃regardless of the influence of the amount or the calcination atmosphere.In the air atmosphere,Cu S reduces Cr（Ⅵ）,and the reduction product Cu Cr₂O₄ is obtained.In the nitrogen atmosphere,when the calcination temperature rises to 800℃,Cu Cr₂O₄ is reduced to Cu Cr O₂.The difference in their reduction products indicates that the ability of Cu S to reduce Cr（Ⅵ）is inferior to that of Zn S.