Currently, one of the main sources of electricity generation is coal-fired power generation. Coal-fired plants generate electricity by burning coal, resulting in a large amount of waste (ash and slag) being accumulated, which has a negative impact on the environment. Involving ash and slag processing will not only reduce the environmental burden, but also provide additional marketable products. Depending on the coal deposits, combustion conditions, and waste composition, ash and slags have different physical and chemical characteristics. Very often, ash and sludge contain elements such as Fe, Si, Ti, Al, Ni, Mo, V, and many others. Various enrichment methods are used to extract these valuable components: flotation, gravity separation, magnetic separation, and leaching.The choice of beneficiation process primarily depends on the size of the material to be processed, as well as the physical and chemical properties of the components that need to be separated.

Ash-and-slag waste (ASH) from thermal power plants (TPPs) was selected to investigate the possibility of extracting iron-containing components. To justify the processing method, studies on the granulometric and chemical compositions were carried out. The material mainly consists of fine particles with a fraction greater than 90 % in the -45 micron size class. At the same time, by electron microscopy, the presence of various microspheres, including aluminosilicates and iron-bearing ones, was established. Due to the small size of these particles, it is difficult to produce concentrates with marketable quality using conventional enrichment methods.

The conducted studies on magnetic fractionation allowed us to establish that the distribution of iron is quite uniform in all fractions, but microspheres, which include magnetite associated with intermetallides, are mainly concentrated in magnetic fractions obtained at current values equal to 2, 3 and 4 A. It was assumed that iron in the compounds is in different valence forms and has different magnetic properties. At the same time, microspheres containing hematite and aluminosilicates were not found in isolated magnetic fractions. It was proposed to use high-gradient magnetic separation to separate such microspheres from finely dispersed materials.

Studies on the influence of various parameters and settings of the magnetic separator, including matrix size, field strength, and pulsation frequency, on the characteristics of extraction and concentration of the target component, were carried out at a high-gradient magnetic separator while varying technological parameters and modes. As a result of these studies, it was found that the best results were achieved with the following operating parameters: magnetic induction of 1.1 T, diameter of matrix rods of 6 mm, and pulp pulsation of 300 rpm. In order to further increase iron extraction in the concentrate, a series of experiments using flocculants were conducted. As a result of the research, a technological mode was proposed that allows for the production of iron ore with a 50% iron content and a recovery of 94.5% in one stage using a magnetic induction of 1.1 Tesla, a matrix bar diameter of 6 mm, a pulse frequency of 300 cycles per minute, and the consumption of Flotifloc flocculant of 100 grams per ton. Scanning electron microscopy revealed that under these conditions, most microspheres containing hematite and aluminosilicate minerals with sizes ranging from 2 to 15 micrometers are extracted into the magnetic fraction.

Thus, for the extraction of microspheres with different compositions and sizes, a sequential magnetic enrichment scheme is recommended: magnetic separation in a weak magnetic field and high-gradient tailings separation. This proposed solution will not only allow us to obtain materials with unique technological properties, but will also reduce the environmental impact in areas where ash dumps are located.

This work was carried out within the grant of the Russian Science Foundation (Project № 23-47-00109).