Study on the difference in adsorption thermodynamics for water on swelling and non-swelling clays with implications for prevention and treatment of pneumoconiosis

Abstract

Excessive inhalation of mineral dust can cause irreversible damage such as diffuse fibrosis of lung tissue. Water-based dust reduction technology can effectively control the dust concentration. The study of the interaction of water-clay mineral dust is helpful to the prevention and treatment of pneumoconiosis by water-based dust removal technology. To better understand the underlying adsorption mechanisms of water molecules on clay mineral dust, the detailed adsorption thermodynamics analysis is necessary. In this paper, we research the thermodynamics of adsorption of water molecules on swelling clay of montmorillonite and non-swelling clay of illite. First, the adsorption isotherms of water molecules on montmorillonite and illite at 293–313 K were measured by gravimetric method. Then, the key thermodynamic variables, including entropy change (Δ S ), surface potential ( Ω ), isosteric heat of adsorption ( Q st ) and variation of Gibbs free energy (Δ G ), were analyzed. Results illustrate that the adsorption amount for water molecules on illite is one order of magnitude smaller than that on montmorillonite, suggesting that swelling clay plays a dominant role in water molecules adsorption process. For water molecules adsorption on montmorillonite, the contribution of secondary adsorption to total adsorption ( a 2 / a ) is always less than 30%. For water molecules adsorption on illite, the contribution of primary adsorption to total adsorption ( a 1 / a ) is greater than a 2 / a at the low pressure region, while a 2 / a can exceed 60% at the high pressure region. The difference in the uptakes of water molecules adsorption on non-swelling and swelling clays is mainly resulted from the difference in primary adsorption on two clays. The Henry’s constant ( K AA ) for montmorillonite is in the range of 21.37–75.08 mmol/g/kPa, which is evidently larger than the K AA values of 0.34–0.98 mmol/g/kPa for illite. Compared with non-swelling clay, the adsorption spontaneity degree for water molecules on swelling clay is higher, and the interaction of swelling clay-water molecules is stronger. Meanwhile, the movement of adsorbed water molecules in swelling clay is more confined than that in non-swelling clay. These findings can offer meaningful guidelines for the prevention and treatment of pneumoconiosis.