Evaluation of variation of salt dust hygroscopic aerosol particle size as a function of relative air humidity

The expansion of mining in potash mines has faced the problem of fresh air shortage, which cannot be solved within the current paradigm of self-contained ventilation. Prospects are related to sequential and recirculation ventilation, as well as the concept of “ventilation on demand”, requiring a detailed description of the processes of “self-cleaning” of a mine air from dust. Crushing a rock mass results in the formation of many aerosol hygroscopic salt particles, which in humid air conditions aggregate and settle on a drift floor. Accurate mathematical models are necessary for predicting the dispersion of these particles and associated gases. The paper considers the regularities and mechanisms of the effect of relative air humidity on the size of salt dust particles, aerosol hygroscopic salt particles of halite (NaCl) and sylvin (KCl). The interactions at the contact “salt surface - humid air” are described and the current understanding of the hysteresis processes and the stages of deliquescence and efflorescence (recrystallization) of hygroscopic aerosol particles are considered. Due to the fundamental difficulties of using modern experimental electronic equipment in the conditions of underground mines, data on oceanic aerosols of the same chemical composition were involved in the analysis. A number of models of hygroscopic growth of oceanic aerosol particles were reviewed and then adapted to the conditions of a potash mine atmosphere that made it possible to obtain average values of the factor of a salt aerosol particle hygroscopic growth. The good convergence of the known scientific data on the changes of the hygroscopic growth factor depending on relative air humidity for both oceanic aerosol and salt dust aerosol characteristic of a mine air was shown. The obtained theoretical-empirical data characterizing the changes in the size of salt particles depending on relative humidity were tested in model studies with salt aerosol. Young’s model was proposed to interpret and predict the changes in the size distribution of salt aerosol particles. The heuristic value of the proposed approach was confirmed by the example of the Young’s model record in log-log coordinates. The results of the study can be applied to calculate the processes of dust conditions formation in rock-salt and potash mines.