High-efficient Clean Processesfor Mineral Resource
For clean production of alumina from low grade resources, a sub-moIten salt technology has been developed to treat the raw materials of diasporic bauxite, Bayer red mud and high-alumina fly ash. With the technology, the digestion pressure and temperature of diasporic bauxite can be reduced from 4.7-6.3 MPa and 260-280℃ in the Bayer process to atmospheric pressure and 150-170℃，respectively, which dramatically improves the digestion operation process conditions and reduces equipment cost. The sub-moIten salt technology is also used to process red mud generated in the Bayer process to realize the recovery of alkali and alumina. Na2O content in the final red mud can be reduced to less than 1％，the residue canbe used to produce building materials in a high proportion. When the sub-molten salt technology is used to process high-alumina f1y ash，the extraction rate of alumina from the ash can be over 90％.
The silica in the ash can be converted to a calcium silicate insulation material with excellent performance, which realizes the resource utilization of all components in the fly ash without discharge of wastes. At present, a demonstration project of clean production technology by the sub-molten salt technology has been built at the scale of 30,000 tons alumina annually. The demonstration project is operated well and stably, which is about to be scaled up over 100,000t/a, as the figure below.