Research On The Effect Of Stainless Steel Slag Tailings On Cement Hydration And Corrosion Resistance

Steel demand is huge in China,and its steel output ranks in the forefront of the world.However,the amount of steel slag discharged from steelmaking is also very huge,with a cumulative amount of more than 1.8 billion tons.As a kind of waste generated in the later stage of stainless steel production,the accumulation proportion of stainless steel slag is more than 30%.It not only occupies a lot of land,causing a waste of resources,but also the leaching of heavy metal hexavalent chromium will cause environmental pollution.How to reuse this kind of waste residue is the focus of our attention.In this paper,the later treated stainless steel slag tail mud is added into cement clinker as a mixture to explore its physical properties and hydration performance,and the leaching value of heavy metals is detected,and the corrosion resistance of cement is also studied.It is hoped to provide theoretical support for the reuse of this kind of waste residue and contribute to resource conservation and environmental protection.Firstly,the chemical composition and mineral composition of the stainless steel slag tailings were firstly analyzed,It was found that it was similar to the steel slag,mainly Ca O,Si O₂,Mg O,A1₂O₃,etc.,and there were many minerals such as C₂S,C₃S,C₃A,C₄AF,which had potential hydraulic properties.Due to the particularity of its production process,the activity of stainless steel slag tailings was poor,and there was a risk of poor stability and leaching of heavy metal hexavalent chromium.In order to eliminate the poor stability by aging treatment and mechanical ball milling,the mixing amount of stainless steel slag tailings should be controlled to control the leaching risk of hexavalent chromium.The experiment verified that the mixing amount of stainless steel slag tailings should not exceed 20%in the cement clinker,otherwise the leaching value of hexavalent chromium will exceed the standard limit of 10mg/kgThe water consumption of standard consistency and the initial and final setting time were within the empirical value,and the stability was qualified.The content of stainless steel slag tailings was less than 20%,and the 28d compressive strength was more than42.5MPa.If the stainless steel slag is added into cement clinker to produce ordinary cement with compressive strength of 42.5MPa,the economic cost is 11.5 yuan/ton less than that of P.O42.5 ordinary cement.The hydration performance was tested in the later stage.The tailmud content was 20%,the hydration calorific value at each age was in the range of 240J/g～370J/g of ordinary Portland cement.when the tailings content was 30%,the hydration heat value of each age was in the range of 230J/g～310J/g of low-heat cement.Microscopic qualitative analysis shows that the addition of stainless steel slag tailings has limited ability to improve the strength of cement,and it mainly increases the strength in the form of micro-aggregate.With the progress of hydration reaction,the content of Ca（OH）₂ in the later stage is the main factor affecting the strength of cement.The water consumption of standard consistency and the initial and final setting time of the cement clinker mixed with stainless steel slag tailings and granulated blast furnace slag were found to be higher than that of the cement clinker mixed with stainless steel slag tailings,but both of them met the requirements of empirical values and were qualified for stability.The content of tailings and slag was in the range of 10%～20%and 10%～30%respectively,and the 28d compressive strength of the two was more than 42.5MPa when they were mixed into the cement clinker.They were mixed into the cement clinker to produce the composite cement with compressive strength of 42.5MPa and 52.5MPa,the economic cost could save 44.5 yuan/ton and 27.5 yuan/ton,respectively,compared with that of P.O42.5 and ordinary cement It was found that the hydration heat value of cement mixed with two kinds of waste slag was in the range of hydration heat value of ordinary Portland cement.Microscopic analysis shows that the hydration activity of slag is higher than that of stainless steel slag tailings,and the two kinds of waste slag can stimulate each other to stimulate the activity,enhance the early hydration reaction rate,and generate AFt,C-S-H gel and other hydration products,which contribute to the strength.The secondary hydration reaction rate of the slag and tailings in the later period is lower than that of the cement clinker,and the accumulation of Ca（OH）₂ causes the increase of the internal void in the cement,which will reduce the strength in the later period as a whole.The corrosion resistance of single-compound stainless steel slag tailings was studied.In Na Cl and Na₂SO₄ salt solutions,the 90d corrosion resistance coefficient was higher than that of blank group.Microscopic analysis showed that the main factors affecting the corrosion resistance were the decrease of cement clinker content and the production of hydration products,which restricted the growth of strength in the later period,leading to the weakening of the corrosion resistance.At the same time,products such as AFt,Ca（OH）₂ and hydrated calcium chloride aluminate produced by mixing waste residue have enhanced anti-erosion effect in the early stage,but in the later stage,due to the expansion effect,the pores inside the cement will increase,affecting the anti-erosion performance.