The results of studies on mineral grains motion regularities in air medium are presented in comparison with regularities of their motion in water, with determination of main differences in the regularities. It was established, that equal-falling factors in air medium with respect to relatively large particles are smaller, than in water settling, both with regard to free and hindered falling, which is evidence of necessity to divide feed material into larger number of size fractions prior to pneumatic preparation. It is shown, that pneumatic dressing is more advantageous under mineral particles hindered-falling conditions, since in that case starting feed may be divided into smaller number of size fractions, and air flows of considerably smaller velocity are required in separation zone.

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