Influence of different dry milling processes on the properties of an attapulgite clay, contribution of inverse gas chromatography

• Dry grinding processes reduce significantly the particle size of attapulgite.
• Short times of grinding preserve the fibrous morphology.
• Long duration of grinding in Pulverisette 0 induces complete destruction of fibres.
• The three examined grinding processes cause the decrease in specific surface value.
• The DF with isopropanol proves that grinding releases new high energy sites.

The effect of dry milling processes on the surface properties of an attapulgite clay, also called palygorskite, was investigated by carrying out experiments with different types of grinding devices. Ground products were then characterized by size measurement, scanning electron microscopy, X-ray diffraction, adsorption–desorption of N2 and inverse gas chromatography at infinite dilution (IGC-ID) as well as finite concentration conditions (IGC-FC). These analyses were performed to evaluate the changes in particle size distribution, morphology, crystallinity and surface properties of attapulgite powder, respectively. Among the tested dry grinding devices, grinding in an air jet mill (Alpine 50 AS) and a vibratory ball mill (Pulverisette 0) led to the most significant particle size reduction. SEM photomicrographs showed that a breakage of the fibrous structure took place during dry grinding. Moreover, long grinding in Pulverisette 0 resulted in the complete destruction of fibre morphology followed by agglomeration. XRD analysis showed that whatever the grinding process, the microstructure of the attapulgite was not affected. IGC confirmed that only grinding in Pulverisette 0 affected the surface properties notably. In this case, the most significant decreases were observed in the dispersive component of the surface energy (164 to 116 mJ/m2) and in the specific surface area obtained with the octane probe (114.5 m2/g to 62.6 m2/g) by IGC-ID and IGC-FC, respectively. At the same time, a modification of the distribution functions of the adsorption energies (DFAE), giving information about surface heterogeneity, was noticed.

In the distribution function of attapulgite obtained with isopropanol probe, the shoulders at high energies are pronounced and become intense, proportionally with the duration of milling in the Pulverisette 0, indicating the occurrence of polar sites, like hydroxyl functions, able to interact with the isopropanol probe.Figure optionsDownload as PowerPoint slide