| As the Chinese steel production has been increasing every year in recent decade, the yield of steel slag, the by-product of steel making process by using large numbers of scraps in electric arc furnace, will inevitably increase. The utilization ratio of EAF slag is only about 10%, less than that of BOF slag. Most slag has been extensively emitted, which wasted large amounts of resources and polluted environment seriously. As there is not a systemic technology to treat EAF slag as yet, the technology of slag resourcfulization is approaching. Recovering the iron from the EAF slag and utilizing residual mud high-efficiently as its starting point, the paper developed a technical route to recover ferritic resource from slag by high-efficiency separation; the residual mud was activated as cement mixed material and concrete additive to produce steel slag cement and green concrete, so as to expanding the approach for comprehensive use of EAF slag. The technical approach would achieve the high-efficiency resourcfulization of EAF slag and improve its value.In view of the question that the recovery rate of iron resource from EAF oxidizing slag is lower, the united concentration of iron including magnetic separation, magnetizing roast, flotation separation and gravity separation was developed. Metallic iron can be screened by 2.5mm screen when slag is crushed; the grade of recovered iron is 89.38%. Magnetic parts can be separated from the slag which size is less than 2.5mm by magnetic separation tube with 312.5mT magnetic field intensity first, the grade of reclaimed high purity iron is 64.34%, but recovery rate is only 38.75%. The results of separation experiments to residual slag by weak magnetic separation show that the grade of recovered iron by gravity separation is 51.47%, which recovery rate is only 37.28%. In the paper, the approach of weak magnetic separation and gravity separation is relatively efficient compared with the other separation way. which can concentrate iron-containing mineral from residual slag, obviously improve the grade of recovered iron. The grade of mixed recovered iron powder is 60.24%, and recovery rate is above 70%, which can be reused in sintering process as raw metallurgy material, realize resourcfulization of ferritic resource in EAF slag.In view of the question that the reactivity and utilization of the residual EAF slag mud is lower, which is the by-product of weak magnetic+gravity separation, the activated effects of residual mud by mechanical-activated and alkali-activated were investigated by experimental way. The results show that mechanical-activated has some effects to the mud activity, but higher fineness is required. The residual mud need to be grinded more than 60 minutes to reach the first level fine powder. Gypsum has better effects to residual mud as a chemical activator, the activity indexes of residual mud blended with 4% hemihydrate gypsum by weight in slag cement are highest, such as A7 and A28 are 81.3 and 82.6 respectively. Na- activator can raise alkalinity in steel slag cement; accelerate the activation of active constituents in the slag mud. Gypsum can activate the activation of slag mud more smoothly; the activation can be released gradually. When the specific surface area of EAF slag mud powder is above 600 m2/kg by grinding, blended with 4% gypsum /sodium which is mixed with 1:I by weight, the best admixed effect is achieved, A7 and A28 of which is 84.65 and 82.73 respectively, the activity of steel slag powder can reach the first level of the national standard.Due to the contradiction between reducing the cementitious activity and improving the cubage stability of steel slag residual mud, the author conducted experiments to compare the performance and hydration law of steel slag cement prepared with EAF slag residual mud and BOF slag residual mud respectively. The results show that the mineral of EAF slag mud mainly is C2S, the amount of CaO is less; but the mineral of BOF slag mud mainly is C3S and Ca (OH)2; the difference of mineral composition is the main reason of the difference of the activity of two kinds of residual mud through wet grinding process. The decreased activity of EAF slag mud was mainly reflected to slow the strength growth in the prepared cement at early age; but that of BOF slag mud was mainly reflected to lower the strength more in the prepared cement at late age. Microscopic analysis showed that the intensity of diffraction peak of C-S-H flocculent gel and the number of needle-like AFt crystal in EAF slag cement are significantly weaker than those in BOF slag cement after being hydrated 3 days. However, after being hydrated 28 days, those in EAF slag cement are significantly stronger. The loss of cementitious activity in EAF slag mud is less than that in BOF slag mud on the whole.25% two kinds of mud respectively blended with 40% cement clinker,30% blast furnace slag and 5% natural gypsum can product steel slag cement, which physical and mechanical performance can reach 42.5 grade of the national standard.Based on the problem which EAF slag residual mud is less added amounts in concrete and poor performance in engineering application, the method of improving the performance of concrete by using the superposition effect of EAF slag mud and blast furnace slag was studied; the influence of EAF slag mud powder on the physical and mechanical properties of the concrete alone or mixed with blast furnace slag powder was disclosed. The analysis to hydration products of concret showed which slag residual mud as admixture can improve concrete performances was mainly reflected to refine the pore space and improve the pore structure; the slag residual mud can improve the pore structure of the hydration products obviously when it was blended in concrete alone after being hydrated 3 days. The effect of the slag residual mud to the pore size distribution of hydration products is not obvious when it was blended in concrete alone at late age, but compound effect or superimposed effect can be fully played when these two kinds of powder were mixed, improve pore size distribution and pore structure of hydrated products, promote the anti permeability, anti chloride ion penetration ability and macro physical and mechanical properties of concrete. The EAF slag esidual mud can replace 10～50% cement paste by weight to prepare C30～C50 low cost commercial concrete when it mixed with BF slag or alone, P.O 42.5 cement aggregate is 440 kg/m3 and water cement ratio is among 0.37～0.45. |
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