Effects of Dry Grinding on the Structural Changes of Kaolinite Powders

Abstract

The present study examined the effects of dry grinding, using ball-milling, on the structure of reference well-crystallized (KGa-1) and poorly crystallized (KGa-2) kaolinite powders from Georgia. Grinding produced a strong structural alteration, mainly along the c axis, resulting in disorder and total degradation of the crystal structure of the kaolinite and the formation of an amorphous product. The surface area increased with grinding time, mainly in KGa-2 (maximum value 50.27 m 2 /g), a result associated with particle-size reduction. These particles became more agglomerated with grinding, and the surface area decreased after 30 min, as confirmed by scanning electron microscopy and particle-size-distribution analysis. There was a limit to particle-size reduction with grinding time. When grinding time was increased, the original endothermic differential thermal analysis (DTA) effects of dehydroxylation in both samples shifted to lower temperatures, decreased in intensity, then disappeared completely after 120 min of grinding. The temperature of the characteristic first exothermic effect shifted slightly to lower temperatures with grinding, although the DTA effects did not increase with grinding time in either kaolinite sample, at least up to 325 min. The amorphous, mechanically activated kaolinite converted into low-crystalline mullite nuclei at a lower temperature than did the unground samples, as deduced by thermal and X-ray observations. This effect was especially important for the KGa-2 sample. Grinding did not seem to influence the formation of silicon-aluminum spinel from kaolinite. The present results may explain why ground kaolinite samples prepared via different routes-e.g., with differences in grinding-behave differently during high-temperature transformations, as reported in the related literature.

The surface properties of clay minerals modified by intensive dry milling — revisited

“…On prolonged milling, a substantial structural deformation and alteration occurs, followed by the transformation of the crystalline structure into an amorphous phase; as recently described by Dellisanti and Valdré (2005) for bentonite, and by and Sanchez-Soto et al, (2000) for kaolinite. The latter study has shown that milling produced vigorous structural changes along the c axis, resulting in disorder and degradation of the crystal structure of the kaolinite and the formation of an amorphous solid.…”

“…The literature also abounds with studies of the influence of mechanical processes on the structural and physico-chemical properties of a variety of clay minerals (Suray et al, 1997;Baudet et al, 1999;Sanchez-Soto et al, 2000;Frost et al, 2001;Franco et al, 2004;Dellisanti and Valdré, 2005;Hrachová et al, 2007;Vertuccio et al, 2009). The rapid development of the new, composite claybased materials has advanced the research and processing of fine-milling and reinforcing methods.…”

Enhancement of nitrogen release properties of urea–kaolinite fertilizer with chitosan binder

“…It can be seen that dry grinding caused reduction in size of the kaolinite particles which has been mentioned in previous studies. [12,37] Mechanism of urea release from nitrogen CRF The proposed mechanism of releasing the urea from NCRF can be described by the following steps: First, the water penetrates inside of the granules through tiny porosities. [2] The weight of granules with chitosan 6% before (0.41 g) and after immersion (0.46 g) in water indicates the penetration of water.…”

Effect of Grinding on Chrysotile, Amosite and Crocidolite and Implications for Thermal Treatment

“…In this regard, although the crystal-chemical transformation induced by the thermal treatment of asbestos is the most common transformation process [14][15][16][17][18][19][20][21][22][23], other processes such as biological treatment, dissolution by acid, thermochemical and mechano-chemical processes have been used for treating ACMs during the last two decades [24][25][26][27][28][29][30][31][32]. In particular, mechano-chemical treatment, which could be used for disposing of and/or recycling asbestos, is capable of increasing particle reactivity [33], reducing the sintering temperature [34] and reducing the thermal decomposition temperature [35,36]. In this regard, Suquet [37] has shown that grinding and/or leaching pre-treatment of chrysotile affected its dissolution in water.…”