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Power properties of particles surface in the product of industrial coal flotation

Jerzy Sablik, Marek Lenartowicz

Results of testing the flotation activity of coals of different coalification degree in a pneumomechanical flotation machine in a function of surface tension of wetting of coal particles were presented. The work objective was to indicate that a sequence of particles flotation in turbulent conditions of process depends on power state of their surface, measure of which can be the surface tension of wetting, and results obtained by film flotation method can be used for testing the parameters of flotation technology and technological efficiency of IZ type flotation machines.

Sampling of IZ type flotation machines, which operate in processing plants and enrich coal of different coalification degree, i.e. gas-and-flame coal of 32.1 type, gas coal of 33 type, gas-and-coking coal of 34.2 type and orthocoking coal of 35.1 type, was carried out in real conditions. Samples of feed, concentrates from each section of two-rotor flotation machines and failings, were tested. For comparison purposes, the samples of coal lumps as clean as possible (of low ash content, i.e. of low content of ash-generating substances) were also tested after grinding, similarly to the products obtained from sampling the IZ type flotation machines. Power properties of surface of particles in samples were tested by film flotation method and a number of determinations by this method was equal to 1491. Moreover, technological and physical-and-chemical analyses, which include determination of coal content, sulphur content, content of volatile compounds, moisture content, ash content in lumps, feed and concentrates as well as failings, were conducted.

Using the tests results, average critical surface tension of wetting, power heterogeneity of surface in tested groups of particles and share of particles of hydrophilic surfaces were calculated for all samples. It was indicated that despite turbulent conditions, in which flotation process takes place in flotation machines, a sequence of coal particles flotation depends on surface tension of wetting. Particles of the lowest surface tension of wetting (of the lowest surface energy), which are of the highest flotation activity, flotate at first (in the first rotor compartments) and the particles of higher surface energy, thus of lower flotation activity, flotate in further rotor compartments. It was also indicated that particles of hydrophilic surfaces move to concentrates, and excessive number of hydrophobic particles moves to failings, what reduces effectiveness of enrichment process. Share of each type of particles in flotation products depends on a degree of coalification of the processed coal. The reasons of disadvantageous phenomenon of moving of hydrophilic particles to concentrates and hydrophobic particles to failings were also analysed. Moreover, direct relationship between surface tension of wetting and ash content and hydrophilic particles in a given group of particles (product of enrichment) was indicated and, on this basis, it was found that hydrophilic particles which move to concentrates are not the particles of organic coal, which have a lot of oxygen bonds, but they are the particles of mineral coal.    

Collected results from tests and calculations enabled an analysis of flotation technologies used in processing plants (assessment of proper selection of technology parameters) as well as assessment of technological efficiency of IZ type machine. With the use of such analyses, the operations, which enable improvement of process conditions and obtaining more advantageous results of coal slurry enrichment in pneumomechanical flotation machines of IZ type, were determined and described.