DefinePK

Abstract

Red mud is solid waste received in the process of obtaining alumina by the Bayer method and is a potentially valuable secondary resource. Currently, the global scientific community is faced with the task of developing environmentally friendly technologies for red mud recycling. Numerous publications discuss both the methods of extracting valuable metals (aluminium, iron, titanium, scandium, rare earth elements), and the use of red mud in building; cement, mineral wool, ceramics manufacturing, etc. This paper summarizes the results of a systematic review of the researches in one specific application area - the extraction of valuable elements (Fe, Al, Na, Ti) from red mud. A total of 162 scientific publications were examined, and 46 of them have been analyzed in the paper. The analysis showed that, depending on the composition of the processed bauxite and the technological scheme for alumina producing, the content of iron oxide (Fe2O3) varies from 7 to 70% by mass, aluminium oxide (Al2O3) - from 2 to 33% by mass, titanium oxide (TiO2 ) from 2.5 to 22% by mass, sodium oxide (Na2O) to 12.5% by mass. The achieved maximum percentage of iron extraction is 97.5%, aluminium - 89.7%, sodium - 96.4%, titanium - 97%. In conclusion, it should be noted that almost all studies have been carried out only in the laboratory conditions. Technological proposals for the integrated processing of red mud are highlighted as the most effective, including the processes of reduction melting, magnetic separation, leaching with mineral (HCl, H2SO4, HNO3) and organic (H2C2O4) acids. Current researches propose to use microwave, ultrasonic radiation, or plasma technologies in recycling. Considering the results and conclusion in the publications observed it seems difficult to conclude about the cost-benefit methods. As a result of the work, a systematizing table of the methods for extracting Fe, Al, Na, Ti from red mud has been proposed. The authors have made some suggestions on the criteria of a technology that would have environmental, energy and economic benefits.