Study On The Interaction Between Tin Removal And Rubber Pyrolysis During The Coupled Roasting Of Waste Rubber And Tin Ore

There are many complex tin-bearing iron ore resources in southwest China.After the Sn-bearing iron ore is processed by traditional gravity separation process,the iron content in the Sn-bearing iron concentrate is as high as 60 wt%,and the tin content is about 0.3-0.8 wt%,if the tin can be removed and recovered from the Sn-bearing iron concentrate by an appropriate method,it can not only solve the problem of iron ore shortage,but also realize the recovery of valuable metals.Due to the large number of used tires produced each year,methods for the efficient disposal of used tires are being studied worldwide.Considering the waste tire rubber(C₁-C₄ hydrocarbons),H₂S,SO₂and COS gas released during the pyrolysis process,which can reduce and vulcanize Sn O₂ to Sn S,this paper proposes a new method for roasting waste tire rubber in N ₂ gas for separating Sn from Sn-bearing iron concentrate.The effects of process paramete rs such as firing temperature,amount of used rubber rubber and firing time on tin separation rate were studied.At the same time,the interaction mechanism of sulphur,tin and iron during sintering of stannite and waste tire rubber was studied in depth.The phases of iron and tin deposits in Sn-bearing iron concentrates are mainly Fe ₃O₄and Sn O₂.The addition of waste tire rubber plays the role of reducing agent and vulcanizing agent for the separation of iron and tin in Sn-bearing iron concentrate.The experimental results show that the tin volatilization rate increases with the increase of the roasting time.Secondly,Sn O₂ in Sn-bearing iron concentrate can be reduced to Sn by CO during roasting,and then sulfurized by SO ₂ and COS to form Sn S and volatilized.A small amount of Sn remains in the form of Fe-Sn alloy in the roasting substrate.However,excessive amounts of waste tire rubber will cause the formation of metallic iron,which will promote the formation of Fe-Sn alloys,leading to a reduction in tin volatilization rate,which is not conducive to the separation of iron and tin.The effect of firing temperature is also important.Fe-Sn alloys are formed at firing temperatures in excess of 1000°C,and the Sn content in the formed Fe-Sn alloys decreases as the firing temperature increases,resulting in the sulfidation and volatilization of Sn in the Fe-Sn alloy will be limited.Under the optimal conditions,that is,the roasting temperature is 1000°C,the roasting time is 60 min,the amount of waste tire rubber is 20 wt%,and the nitrogen flow rate is 100 m L/min,the iron phase in the Sn-bearing iron concentrate is only reduced to Fe O.At the same time,tin is volatile as volatiles,and the tin content in the substrate is reduced to 0.062 wt%.In order to further study the pyrolysis behavior of waste tires in the process of Sn removal,the yield and characteristics of pyrolysis products during the experiment were analyzed.We have found that increasing the roasting temperature will increase the gas composition,but will reduce the yield of solid and petroleum fractions.The Sn-bearing iron concentrate contains a large amount of Fe₃O₄,which reduces the content of CH₄and H₂ in the pyrolysis gas products of w aste tires,and reduces the C/H ratio and calorific value in oil,but it promotes the volatilization of sulfur-containing substances in coke Furthermore,the tin in the Sn-bearing iron concentrate is vulcanized to volatilize it,and the direct use of coke is realized.The Ca O-Mg O in tin-bearing iron concentrate gangue can prevent hydrocarbons from forming a stable chemical structure,accelerate the degradation of hydrocarbons,and make it easier to dissociate.Therefore,gangue in Sn-bearing iron concentrates can slightly increase the yield of derived oil and combustible gas,and further improve the quality of pyrolysis oil.