| As a major producer of alumina,alumina production capacity has reached to 69.017 million tons by the end of December 2017,accounting for more than 50%of the total global production capacity.With the rapid increase of alumina production in China,the large amount of red mud generated is urgent for effective treatment methods.In view of the intractability of the Bayer process’s red mud,the group proposed a new process for treating red mud with the"calcification-carbonization method".The 80%of the alkali and more than 40%of the alumina in red mud can be recoved by this process and the product new type red mud mainly consist of calcium carbonate and calcium silicate,which can be used in the cement industry.In this paper,based on the calcification-carbonization method,calcium carbide slag was used as calcium source for calcification process instead of calcium oxide.The specific research contents and results are as follows:(1)The thermodynamic study of the calcification of calcium carbide slag as a calcium source indicates that Ca3TiFeSi3O12 can steadily exist in calcified slag in the temperature range of 273～573K,and the increase of reaction temperature help to the formation of Ca3TiFeSi3O12.(2)Three kinds of calcium source calcification single factor experiments showed that under the calcification conditions of calcium-silicon ratio of 2.5,calcification temperature of 160℃,liquid-solid ratio of 5:1 and reaction time of 60 minutes,all three calcium sources can achieve superior calcification effect.The Na2O content can respectively reduced to 0.39%(calcium oxide as calcium source),0.30%(new calcium carbide slag as calcium source),and 0.47%(old calcium carbide slag as calcium source).The results of phase analysis of calcified slag showed that the main phase in calcification slag of three calcium sources was hydrating garnet.The unit cell parameters and average grain size of the hydration garnet in the calcified slag were calculated by XRD pattern fitting,and the silicon saturation coefficient of the hydration garnet in calcified slag under different calcification conditions was calculated by the cell length method.The results showed that under the same calcification conditions,the average grain size of hydratable garnet in three kinds of calcium source calcification slags was calcium oxide>new calcium carbide slag>old calcium carbide slag;the saturation coefficient of hydration garnet in three kinds of calcium source calcification slag increased gradually with increasing temperature.(3)The carbide slags main phase of the three calcium source is calcium carbonate,as well as a small amount of hydrated garnet and calcium silicate.The calcification temperature has a great influence on the formation of CaSiO4 phase in carbide slag.The calcification temperature increases led to the increases in diffraction peak of CaSiO4 phase,but the calcification time and calcium-silicon ratio have no obvious effect on the carbonization process.The XRD pattern and micro-morphology of the carbide slag were basically same under different calcification ratios of calcium to silicon and calcification time.(4)Based on the detection results of molten aluminum slag,the extraction rate of Na2O and Al2O3 in the molten aluminum slag under different calcification conditions were calculated.The extraction rates of Na2O from the three calcium source molten aluminum slags were similar vaule under the same calcification conditions.Under the best calcification conditions,the extraction rate of Na2O respectively achieved to 94.58%(calcium oxide as calcium source)and 92.43%(new calcium carbide slag as calcium source),94.71%(old calcium carbide slage as calcium source).The optimum extraction rate of Al2O3 in molten aluminum slag respectively achieved to 33.60%(calcium oxide as calcium source),25.84%(new calcium carbide slag as calcium source),29.28%(old calcium carbide slag as calcium source). |
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