Effect of high-temperature treatment on water vapour sorption of montmorillonite

Abstract

The changes and associated mechanisms in water vapour sorption of montmorillonite after high temperature treatment remain unclear. Here, we hypothesize that water vapour sorption behaviors of montmorillonites treated at high temperatures (>200 ℃) are different from that of untreated montmorillonite. Thus, the objective of this study is to investigate the effect of high temperature treatment on water vapour sorption of montmorillonite. Two successive adsorption/desorption isotherms and the physicochemical properties of pristine montmorillonite (CK) and the montmorillonites treated at 200 ℃, 350 ℃, 500 ℃ and 800 ℃ (marked as M200, M350, M500, and M800) were determined. The first and second water vapour adsorption/desorption isotherms of CK and M200 exhibited a type II, and that of M800 exhibited a type III. For the M350 and M500, the first adsorption isotherms showed a type III, but the first desorption and second adsorption/desorption isotherms showed a type II. The high-temperature heating decreased the water content change (WCC) in the water activity (aw) range from 0.05 to 0.2 (WCC0.05-0.2), and the degree of decrease became larger with increasing heating temperature. For the M350 and M500, the decrease in WCC0.05-0.2 during the first adsorption was greater than that at the second adsorption. Comparing with the CK, the treatments of 200 °C and 350 °C increased the WCC0.2-0.6 during the first adsorption by 33.0% and 28.1%, respectively, and increased the WCC0.6-0.93 during the first adsorption by 17.3% and 31.3%, respectively, but had little effect on the WCC0.2-0.6 and WCC0.6-0.93 values during the first desorption and second adsorption/desorption. Except for the increase in WCC0.6-0.93 during the first adsorption for M500, the WCC0.2-0.6 and WCC0.6-0.93 of M500 and M800 was decreased during the two successive adsorption/desorption processes.