A novel method to calculate the gas adsorption of mixed minerals

Five groups of methane isotherm adsorption tests were carried out at 61 °C under a pressure range of 0–25 MPa, including four groups of pure clay minerals (illite, montmorillonite, chlorite, kaolinite, for brief they are expressed as Ill, Mont, Chl, and Kaol respectively) and a group of mixed minerals by four pure clay minerals in equal mass ratio. The experimental results showed the order of methane adsorption of pure clay minerals: Kaol > Ill > Mont > Chl. And the composition of clay minerals was obtained by XRD experiments. The result showed that the four samples were of high purity, both of which were greater than 90%. In addition, the results of low-pressure nitrogen adsorption experiments showed the order of specific surface area: Kaol > Ill > Mont > Chl, which is consistent with the order of methane adsorption. The methane adsorption is positively correlated to the specific surface area. The adsorption data was fitted to the Langmuir–Freundlich model to establish the method to calculate the adsorption of mixed minerals. The result showed that the parameters of the adsorption model of mixed clay minerals can be obtained by summing the parameters of the adsorption model of the pure minerals contained in the mixture according to their constituent mass ratio and the feasibility of this result was also verified by literature data. Overall, once the mass ratio in mixed clay minerals gets known, its theoretical adsorption can be calculated.