Effect of acid treatment on surface properties evolution of attapulgite clay: An application of inverse gas chromatography

In this paper, the evolution of structural, textural and surface properties of attapulgite after treatment with increasing concentrations of hydrochloric acid (0.5, 1, 3 and 5 M) is reported. The solids obtained were characterized by SEM, XRD, FTIR and BET analysis. The surface properties were also evaluated using inverse gas chromatography at infinite dilution (IGC-ID) and finite concentration (IGC-FC). The IGC analysis permitted us to reach several parameters such as: specific surface area, BET constant with organic probes and the distribution functions of the adsorption energy sites on the solid surface. At dilute concentrations of acid, carbonates are eliminated and the specific surface area increases. However, the morphology and crystal structure of attapulgite are preserved. At higher concentrations of acid, dissolution of octahedral sheets and at the same time formation of an amorphous silica from the tetrahedral sheets occur. However, the fibrous morphology is still preserved. The calculation of distribution functions reveals a clear evolution in the heterogeneity of the surface during the acid treatment, the appearance of shoulders is attributed to the development of strong specific interactions between the injected polar probe and silanol groups on the surface of amorphous silica formed during the acid treatment.

The distribution function DF of the adsorption energy sites of the studied attapulgite, DF obtained by IGC at finite concentration and related to the surface heterogeneity, becomes clearly bimodal reflecting an evolution toward an amorphous silica with increasing the acid concentration.Figure optionsDownload as PowerPoint slideHighlights
► Mild acid treatment involves the removal of impurities such as carbonates.
► Intense acid treatment causes destruction of the clay crystalline structure.
► IGC analysis gives informations about the surface properties evolution of clay.
► The formation of amorphous silica is visible on DF, obtained with isopropanol.