Assessment of the flotation activity of reagents in terms of the hydrogen bond energy in molecular complexes with active sites of the coal surface

Abstract

The hydrogen bond energy of molecular complexes between a flotation reagent and coal’s organic mass is calculated for the first time. The electron density distribution in molecules of 2-methyl-1,3-dioxane and 2-methyl-1,3-dioxa-2-silacyclohexane is determined. It is shown that the silicon atom in the molecule of 2-methyl-1,3-dioxa-2-silacyclohexane increases the electron density at oxygen atoms from −0.279 to −0.424 and −0.432 in positions 1 and 3 of the molecule, respectively. This increases the hydrogen bond energy of the reagent in molecular complexes with water and model compounds of the coal’s organic mass. In molecular complexes of 2-methyl-1,3-dioxa-2-silacyclohexane with model compounds of the coal’s organic mass, the hydrogen bond energy is considerably higher than in corresponding complexes of 2-methyl-1,3-dioxane. As a result, the adsorption of 2-methyl-1,3-dioxa-2-silacyclohexane on the coal surface is 35–45% greater than for 2-methyl-1,3-dioxane. Consequently, the coal grains become more hydrophobic, and their flotation is improved. With the same consumption of reagents, the use of 2-methyl-1,3-dioxa-2-silacyclo-hexane rather than 2-methyl-1,3-dioxane increases the concentrate yield and reduces the losses of the coal’s organic mass with the wastes. Analogous flotation properties of coal are found for other cyclic acetals and their silicon analogs. Experimental data confirm that the hydrogen bond energy in complexes between the flotation reagent and the coal’s organic mass may be used to assess its effectiveness.