Study On Effect Of Ethylene-diamine-tetra-acetic Acid On Carbonation Process Of Steel Slag

Steel slag（SS）,as a kind of misplaced industrial solid waste,has hydration activity due to the presence of mineral phases such as tricalcium silicate and dicalcium silicate,showing great application potential in concrete and cement.Its annual domestic output exceeds 100 million tons.However,the hydration activity of steel slag is weak.Since the presentation of f-Ca O,f-MgO and RO phase,the steel slag has a volume instability,which limits its practical application.This topic begins from the wet carbonation of SS,focusing on the fact that a large number of SS in our country needs rapid and efficient treatment.Ethylene-diamine-tetra-acetic acid（EDTA）is used as the admixture to accelerate the wet carbonation of SS and improve its properties.Meanwhile,carbon capture is achieved.The carbonation process and mechanism of SS with EDTA was investigated,and the feasibility of continuous wet carbonation was explored.The stability of carbonated steel slag（CSS）-cement slurry samples and strength of CSS-cement mortar samples were investigated.In addition,the RO phase（MgO-x FeO-y MnO phase）was further simulated and synthesized,and the hydration and carbonation potential of MgO-x FeO-y MnO phase was investigated.The development of carbonation degree and stability of carbonated MgO-x FeO-y MnO phase with EDTA was studied.The carbonation process of SS with EDTA was investigated.The results show that the mineral phase composition of SS includes calcium-containing gelling phase,RO phase,calcium ferrite,f-Ca O and f-MgO.The acidity and chelation ability of EDTA can accelerate the carbonation process of SS and the carbon sequestration of SS increases with the increase of EDTA.SS with1 g/L EDTA reached a CO₂ sequestration rate of 14.3 g/100 g sample after 60min of wet carbonation.The carbonation product is mainly calcium carbonate particles,the morphology of which change with the extension of reaction time.The calcium carbonate crystal form is always calcite.The f-Ca O of CSS with EDTA was effectively eliminated and the stability greatly improved.The generated fine calcium carbonate is conducive to promoting the hydration and densification of CSS-cement materials.The28-day compressive strength of the mortar sample containing CSS with EDTA increased compared with the control group.The maximum increase is4.91MPa.The continuous wet carbonation process was carried out by recycling solvent.EDTA plays a catalytic role and accelerates the wet carbonation of SS,and part of it is released back into the solution after the carbonation.Although the promotion effect decreases after each cycle,the carbonation degree of the third circle group is still higher than that of the control group.At the later stage of carbonation,there is still some residual Fe-rich phase,showing a poor carbonation activity,which may be RO phase or other inert phases.Hydration experiments were conducted on the synthetic RO phase and the control group.It is found that one of the reasons for the low hydration activity of RO phase is the formation of continuous solid solution at high temperature.RO phase hydration ability is low,but with the extension of time RO phase will continue to hydrate.The characteristic of delayed hydration will cause stability risks.Carbonation can help eliminate the RO phase and the products are mainly Lansfordite and Siderite.EDTA promoted the dissolution and elimination of RO phase during wet carbonation process,but did not promote the formation and precipitation of magnesium carbonate.Through the autoclaving experiment,it was found that the expansion rate of carbonated RO phase with EDTA was reduced by 10.39%compared with the original RO phase expansion rate,indicating that the stability of carbonated RO phase was improved.