Study On Forming And Properties Of Red Mud Fly Ash Sintered Brick

As a powerful aluminum industry country,China produces a large amount of red mud in the process of alumina production every year.According to the statistics,the annual stock of red mud is close to 5000 tons in China,and the accumulated stock has reached 1.1 billion tons,while the reuse rate is only 15%.The accumulation of these solid wastes not only occupies a large amount of land area,but also causes serious pollution to water and soil resources.Consequently,the redevelopment and reuse of red mud as a resource has a strong practical value for improving environmental pollution and realizing the green development of alumina enterprises.Considering that Si,Al,Ca and other elements in red mud are similar to the raw material clay of traditional brick products,in this project,Bayer red mud and other wastes were used as the main raw materials to prepare sintered brick.The specific research contents are as follows:In this paper,the physicochemical properties of red mud were analyzed by means of TG-DSC,XRD and XRF,which provided a theoretical basis for the formulation of the forming process and heating schedule of red mud sintered brick.Secondly,the effects of red mud content,forming pressure,sintering temperature and holding time on the properties of red mud fly ash sintered brick were studied.Through co MParing the analysis,the best sintered brick was selected and the phase change and sintering mechanism were studied.Finally,red mud fly ash sintered brick was prepared on the brick machine produced in industry.The effects of red mud content and sintering temperature on the frost resistance and floating hoarfrost performance of red mud fly ash fired brick were studied,and the mechanism of floating hoarfrost was analyzed.Through the study of the basic properties of red mud,it can be seen that red mud mainly contains Si,Ca,Al,Fe and other elements,which is similar to the main components of clay,and the main particle size is 0.075 mm,which can be used as the preparation material of brick.According to the TG-DSC analysis of red mud,when heated at about 260?and 660?,a certain oxidation reaction will take place in red mud.In order to fully react and release gas,the sintering process of red mud in brick making process is established by holding at 260?and 660?for 30 min.Combined with single factor experiment method,the influence of red mud content,forming pressure,sintering temperature and baking holding time on the loss on ignition,bulk density,compressive strength and water absorption of red mud fired brick were discussed.After co MParing the experimental results,the best forming conditions of red mud fly ash fired brick are obtained,that is,the ratio of red mud to fly ash is 7:3,the forming pressure is 19 MPa,the highest roasting temperature is1050?and the holding time is 2 h.At this time,the red mud fired brick has the optimum performance,in which the loss on ignition is 8%,the bulk density is1.79g/cm³,the water absorption is 18%,and the compressive strength can reach 24MPa.Heavy metal leaching experiments were carried out on the sintered brick which has the best performance and its raw materials,the results show that the leaching amount of heavy metals in sintered brick is much lower than that in raw materials.The sintered brick of 200 mm×100 mm×30 mm was pressed by industrial equipment.By exploring the influence of sintering temperature and raw material ratio on the frost resistance and floating hoarfrost of sintered brick,it is found that the content of red mud has an obvious influence on the frost resistance,while the sintering temperature has a conspicuous influence on the floating hoarfrost of sintered brick.When the content of fly ash reaches 50%,the brick will break in the process of frost resistance;when the content of red mud is 70%,the brick has better frost resistance,and its freeze-thaw loss rate is only 0.5%.When the sintering temperature is from 950?to 1100?,a small amount of white frost will be produced.When the brick is not sintered,a large amount of white frost will be produced.The chemical composition of the floating hoarfrost material is mainly Na₂SO₄and Ca SO₄,which can be detected by XRD.