Study On The Corrosion Behavior Of 12Cr1MoV Steel With Sulfur In Sodium Aluminate Solution

High-sulfur bauxite is produced by the Bayer process.The sulfur in the ore will mainly enter the sodium aluminate solutions in the form of S^2-and S₂O₃^2-,which will seriously corrode the production equipment.The research group conducted a systematic study on the dissolution pipeline material of alumina plant material 20Cr,the commonly used tank material Q235 and 16Mn steel.In this paper,12Cr1MoV steel,a steel commonly used in casing heat exchanger,was selected as the research object.The influence of S^2-and S₂O₃^2-in sodium aluminate solutions on its corrosion behavior was studied by means of high temperature immersion and electrochemical test,and the corrosion mechanism has been analyzed.The conclusions are following:The corrosion rate of steel was accelerated with the increase of concentration when sodium aluminate solution containing different concentration of S^2-was corroded for 5 d.At 1-3 g/L,OH^-adsorbs on the surface of 12Cr1MoV steel to form relatively dense iron oxides.The corrosion products on the surface of steel include Fe₃O₄,FeS,FeS₂ and Fe OOH.At 4-5 g/L,Cr₂O₃ and Fe₈S₁₀ were formed.When the sodium aluminate solutions containing 3g/L S^2-was corroded for 1-5 d,the equation of corrosion rate is:V=6.655+19.486*exp?t/-1.254?.Firstly,Fe₃O₄ and Fe OOH were the main corrosion products with fast corrosion rate.In the middle stage of corrosion,S^2-would destroy the product layer on the surface of steel,and pitting pits will appear.The pitting pits are mainly FeS₂ and Fe₈S₁₀.Then,the formation of sulfide destroys the structure of Fe₃O₄ and Fe OOH corrosion product layers,which were easy to fall off from the steel surface and weaken the protection of steel matrix.When the sodium aluminate solutions containing 5g/L S₂O₃^2-corroded for 1-5 d,the equation is:V=1.946+10.079*exp?t/-1.201?.In the pre-film stage,Fe oxides were produced,and the adsorption of steel to Al O₂^-in the solution lead to the decrease of adsorption,and the corrosion current density of steel is larger and the corrosion rate is faster.In the film forming stage,Fe₃O₄ product film is formed,which will strengthen the adsorption of Al O₂^-,have a strong protective effect on the steel substrate,and the corrosion current density was obviously small,and the corrosion rate is significantly slowed down.When the sodium aluminate solutions with different concentration of S₂O₃^2-was corroded for 5 d,the corrosion rate of steel was accelerated with the increase of concentration.At lower concentration?less than 3 g/L?,the corrosion of steel is not serious,the products were constants of Fe OOH,Fe₂O₃,Fe O,and Al O₂^-was easy to form Al?OH?₃ and adsorb on the surface of steel to form Al?OH?₃.At a high concentration?greater than 3 g/L?,it was beneficial to generate Fe₃O₄.The results of electrochemical experiments showed that the corrosion current density increases with the increase of S₂O₃^2-concentration,the impedance of the corrosion product layer also increases and the corrosion rate gradually accelerates.When the solution mixed with 5 g/L S^2-and 3 g/L S₂O₃^2-corroded for 1-5 d,the equation is:(1=100.131+699.123*exp?/-1.343?.The corrosion process was film formation,transformation and growth.The final corrosion product mainly contained Fe₃O₄,while the outer layer was mainly composed of FeS,FeS₂ and Fe₂O₃.The electrochemical results showed that the iron sulfide compounds would be oxidized to chemically stable iron oxides,leading to further passivation,and the corrosion resistance was the highest at 5 d.The higher the corrosion temperature,the greater the corrosion rate.The lower temperature?90°C?,the sulfide generated was Na FeS₂·H₂O.When the temperature is high?130,150°C?,FeS₂ was formed.In the sodium aluminate solution,S^2-is more corrosive to 12Cr1MoV steel than S₂O₃^2-,and the corrosion rate of steel is fast.When both exist at the same time,the coordinated corrosion rate of steel is significantly accelerated,and the increase in temperature will accelerate the coordinated corrosion rate.