Relationships Between Physicochemical and Structural Properties of Commercial Vermiculites

Abstract

This study examines the effects of thermal (1000 °C), hydrothermal (100 °C), mechanochemical (ambient T), and microwave (~100 °C) treatments on three types of Chinese vermiculites, one with lower potassium content than the others. The goal was to obtain materials with enhanced properties related to specific surface areas. The response of the vermiculites to treatments and their physicochemical properties were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTG), and textural characterization via the BET method. XRD analyses showed similar mineral composition in treated and untreated samples, but the treatments affected the intensity and width of phase reflections, altering crystallinity and structural order, as well as the proportions of vermiculite, hydrobiotite, and phlogopite. Thermogravimetric analysis revealed two mass loss stages: water desorption (from 25 °C to about 250 °C) and recrystallization or dehydroxylation (above 800 °C). The isotherms indicated mesoporous characteristics, with hydrothermally CO2-treated samples having the highest specific surface area and adsorption capacity. The samples with vermiculite, hydrobiotite, and phlogopite generally showed moderate to high specific surface area (SBET) values, and mechanochemical treatments significantly increase SBET and pore volume (Vp) in the vermiculite and hydrobiotite samples. Crystallinity affects SBET, average Vp, and average pore size, and its monitoring is crucial to achieve the desired material characteristics, as higher crystallinity can reduce SBET but improve mechanical strength and thermal stability. This study highlights the influence of different treatments on vermiculite properties, providing valuable insights into their potential applications in various fields (such as thermal insulation in vehicles and aircraft, and the selective adsorption of gases and liquids in industrial processes, improving the strength and durability of building materials like cement and bricks).