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20 min, the effect of slag-iron separation is the best, the maximum nuggets size is 15.0 mm, the nuggets recovery ratio and Al2O3 grade are 97.74% and 42.98%, respectively. The Al2O3 grade of melting slag increased by 16.52% than bauxite, the high alumina slag is mainly composed of alumina (α-Al2O3), calcium hexaluminate (CaO?6Al2O3) and gehlenite (Ca2Al2SiO7), the content of hercynite (FeAl2O4) and metallic iron (Fe) is lower in the slag. When the slag basicity is 3.60~4.10 (C/A=1.4~1.8), the melting slag is mainly composed of dicalcium silicate(Ca2SiO4) and mayenite (Ca12Al14O33). In the case of optimal basicity is 3.60 (C/A=1.4), when the reduction and melting temperature is 1450℃, C/O is 1.4, additional CaF2 content is 2.0%, the reduction and melting time is

20 min, the effect of slag-iron separation is the best, the maximum nuggets size is 11.74 mm, the nuggets recovery ratio is 92.79% and the alumina grade changes a little. Flue gas analysis shows that, the volume fraction of pellets has a important effect on the furnace atmosphere. The pellets volume fraction is higher, the CO concentration is higher which is released by carbon gasification reaction and reduction reaction. When the pellets volume fraction is 1.7%, the reduction and melting temperature is 1400℃, the furnace gas is mainly composed by CO and CO2 and the furnace atmosphere is mainly reducing atmosphere. The maximum gas concentration of CO and CO2 were 58.9 vol% and 17.8 vol%, respectively. The maximum concentration ratio (V (CO) /V (CO2 ) is 3.31. The reducing atmosphere promoted the reduction of carbon composite bauxite pellets and effectively prevented the further oxidation of metallized pellets. Calcium aluminate slag utilization research shows that, using A-C2AS-CA6 melting point slag as refractory aggregate, adding 6.07~24.26% high purity alumina powder, calcining at 1400℃for

4 h, the A-CAS2-CA6 high temperature composite refractory material with good performance can be obtained. The A-CAS2-CA6 composite refractory material is mainly composed by orthohexagonal calcium hexaluminate (CaAl12O19), granular alumina (α-Al2O3) and anorthite (CaAl2Si2O8). The refractoriness is higher than 1600℃, compressive strength is above 38.7 Mpa, linear changes on reheating are +0.1~-0.4%. Self powdering experiments show that, When the slag basicity is 3.60~4.10, the powdering slag ratio whose fineness is over

80 mesh can reach 98.51% by furnace cooling, the powdering slag can be used for the preparation of composite portland cement (C2S-C12A7). Research shows that adding appropriate amount of powdering slag has no adverse effect on the strength of Portland cement. When the slag basicity is 3.85 (C/A=1.6), powdering slag addition should be controlled within 10~30wt%, the optimum powdering slag addition is 20wt%. When the powdering slag ―3― addition is 20wt% and cured in water for

50 days, the flexural strength of Portland cement is the maximum (9.1 MPa), compression strength is 45.7 MPa, which can meet the strength requirement of Portland cement (42.5 MPa), the initial setting time and the final setting time are

185 min and

235 min, respectively. The standard consistency and mobility ratio are 27% and 104%, respectively. When the C/A is 1.0, the alumina leaching rate is the lowest, about 35%. When the C/A increases to 1.2, the alumina leaching rate increases obviously, the alumina leaching rate is over 70%. When the C/A is 1.4, the alumina leaching rate reaches the maximum, the alumina leaching rate is above 80%, when the C/A increases to 1.6 and 1.8, the alumina leaching rate decreases slightly. 论文主要创新点 1. 采用三种碱度条件........