A problem of complex processing of Estonia alum shale as a raw material metallurgy

At present, investigations into the technology of extracting metals from Estonian alum shale allow us to draw the following conclusions .
- Statements in the technical literature about the absence of research into the Estonian alum shale technology are not true.
- The respective technological research was carried out in a number of research institutes in the Soviet Union in 1944-1975. The most promising
methods worked out by them are the following.
- The method of heap bacterial leaching of metals from lump material of alum shale developed in the All-Union Institute of Mineral Raw Materials. This is the simplest method which does not require building of big plants and large expenses for chemical agents, and still enables us within 3 to 5 months to extract from alum shale 70 to 80 % of uranium, 40 to 60 % of molybdenum and 13 to 20 % of vanadium. The principal drawbacks of the method, besides incomplete utilization of alum shale, are the need for a large territory for the industry and pollution of the environment.
- The method of oxidizing autoclave leaching of alum shale with subsequent sorption extraction of uranium from the acid pulp with anion-exchange resin.
In this process, extraction of uranium into solution during 2 to 4 hours is 73 to 76 %. The extraction of other metals was not even considered and thus, the method developed in the AU-Union Research Institute of Chemical Technology cannot be considered economical.
- The sulfuric acid method of complex extraction of metals developed in the Institute of Chemistry, Academy of Sciences of the ESSR. It involves burning the alum shale in a fluidized bed at 800 °C and subsequent processing of ashes by sulfuric acid. In this case, extraction of elements into solution is as follows, %: U and V 80 to 90, Mo 65 to 75, Ti and Fe 60 to 70, Al 40 to 50, K 25. Aluminium potassium sulfate (alum) is crystallized from the sulfuric acid solution as a marketable product after further purification. The remaining residue is processed into ceramic.
According to calculations, consumption of sulfuric acid is 388 kg of 100 % acid per 1 t of ashes. Such a high level of consumption of sulfuric acid makes this process at present impractical since there are no sufficiently efficient methods for sulfuric acid regeneration yet.