Basic Research On Separation Of Tin From Tin-containing Iron Concentrate By Sulfidation Roastin

With the continuous expansion of tin smelting capacity,high-quality tin resources are consumed,and the reserve of it can only be exploited for more than 20 years in the world.At present,the mining grade of tin ore is declining,and the mining grades of vein tin ore and stream tin are more than 0.5 wt.%and 0.005 wt.%respectively,resulting in a large amount of tin concentrate imported from abroad.The tin-bearing iron concentrate is relatively rich,which contains>60 wt.%Fe and 0.3 wt.%-0.7wt.%Sn.Sn exists mainly in the form of fine-grained cassiterite and closely embeds with Fe phase,which is difficult to be widely used in the existing tin beneficiation and metallurgy process.Thus,recovering tin from tin-bearing iron concentrate can improve the availability of tin resources,which is of great significance to the sustainable development of tin metallurgy.In the sulfidation volatilization process,the tin volatilization ratio is more than 90%,and the roasted residue can be used for ironmaking,realizing the comprehensive recovery and utilization of resources.This method has broad industrial application prospects,but its basic research is not clear.The tin removal in the sulfidation roasting process includes:the reduction of cassiterite（tin dioxide,Sn O₂）in tin-bearing iron concentrates and the sulfidation of reduced tin products.Taking tin-bearing iron concentrate as the research object,the goal of this paper is to carry out theoretical and experimental research on tin sulfide roasting.The main innovative results are as follows:Based on the Sn-O phase diagram,the reduction and volatilization behavior of Sn O₂ in CO+CO₂ mixed gases are determined.The results indicate that the reduction path of Sn O₂ is mainly related to roasting temperature.In the temperature range of 729K-1313 K,the reduction path of Sn O₂ includes two stages.When the CO content is less than 17.26%at 1273 K,Sn O₂ can be reduced to Sn O（g）.With the further increase of CO content,Sn O₂can be directly reduced to Sn（l）,and a small amount of Sn can further react with Sn O₂ to form Sn O（g）,promoting the tin volatilization.When the roasting temperature increases from 1313 K to 1900 K,the reduction path of Sn O₂ can be divided into three stages.Due to the increase of the saturated vapor pressure of Sn O,Sn volatilization increases significantly when Sn O₂ is reduced to Sn O（g）in a weak reduction atmosphere（CO content is less than 11.23%）.With the increase of CO content,Sn O₂ can be reduced to Sn O（l）.When CO content exceeds 15.25%,Sn O₂ is first reduced to Sn O（l）and then to Sn（l）.Based on the Sn-Fe-C-O thermodynamic systems,the effect of iron phase in tin-bearing iron concentrate on the Sn transformation behavior is determined during sulfidation volatilization process.Sn O₂ can be reduced to Sn O（g）under weak reducing atmosphere.At higher pyrite（Fe S₂）amount,Sn O（g）can be transformed to Sn S（g）with existence of S₂（g）and SO₂（g）.Meanwhile,part of Sn²⁺in Sn O（g）can replace Fe²⁺in Fe₃O₄ to form Fe-Sn spinel(Fe_xSn_3-xO₄,x=0-1.0),restricting Sn volatilization.A small amount of Sn O（g）can also undergo redox reaction with Fe₃O₄,resulting in Sn⁴⁺replacing Fe³⁺.With the increase of CO content,Sn O₂ and Fe_xSn_3-xO₄ can be reduced to Sn（l）and Fe O,and meanwhile Sn（l）can be sulfurized to Sn S（g）by S₂（g）,COS（g）and SO₂（g）.The tin volatilization ratio in the tin-bearing iron concentrate reaches 98%.However,higher CO content promotes the formation of Fe-Sn alloy,which restricts the volatilization of Sn.In addition,Fe S₂ can decompose into Fe S,which can be oxidized to Fe O and SO₂（g）in CO+CO₂ mixed gases.The sulfur transformation behavior and tin removal path in the roasting process of waste tire rubber and tin-bearing iron concentrate are proved.During sulfidation roasting process,waste tire rubber can decompose into CO（g）,H₂（g）,H₂S（g）,SO₂（g）and COS（g）,and Sn O₂ and Fe₃O₄ in tin-bearing iron concentrate can be transformed to tin-based Fe-Sn alloy and then to Sn S（g）.Under the optimum process conditions,the Sn and S contents in the roasted residue decrease to 0.020 wt.%and 0.022 wt.%,respectively.However,it is difficult to realize the separation of Fe and Sn in high-Sn complex iron resources due to coupling of C and S in waste tire rubber.Inorganic sulfur（waste gypsum and pyrite）can be used to treat high-Sn tin-bearing iron concentrate.Based on Fe S₂+Fe₃O₄+CO+CO₂system,Ca SO₄+Fe₃O₄+CO+CO₂system and experimental results,the transformation path of pyrite and waste gypsum（Ca SO₄·2H₂O）with tin-bearing iron concentrate during roasting is revealed,respectively.Fe S₂ can decompose into Fe S and S₂（g）,and most of S₂（g）volatilizes and has no effect on tin volatilization.Fe S can be transformed into SO₂（g）and COS（g）in CO+CO₂ mixed gases,and COS sulfidation reaction is the main tin removal reaction.In the mixed gases of CO and CO₂,Ca SO₄·2H₂O is mainly transformed into Fe S and Ca₃Fe₄S₃O₆.The Ca₃Fe₄S₃O₆ can be converted into Fe S with increase of CO content.Both Fe S and Ca₃Fe₄S₃O₆ can be transformed into SO₂（g）and COS（g）in CO+CO₂ mixed gases,and Sn can be sulfided into Sn S（g）.Under the same Sn removal result,the amount of curing agent decreases by 20%with addition of waste gypsum,and meanwhile it realizes the circulation of sulfur in the sulfidation roasting system.Through systematic research,this paper constructs the theoretical system of sulfidation roasting of tin-bearing iron concentrate,which lays a theoretical foundation for the industrial application of complex tin-bearing iron resources.