Spheroidal halloysites from Patagonia, Argentina: Some aspects of their formation and applications

Abstract

Halloysite deposits in Argentina have been identified in the province of Río Negro (Patagonia). The mineralized area occurs as altered zones in Eocene volcanic-pyroclastic rocks, dacitic to rhyolitic in composition. A comprehensive study of these deposits was carried out by means of mineralogical, geochemical and isotopic analyses. Intense weathering has transformed the whole rock to a white mass composed of 75% -90% halloysite + kaolinite, with cristobalite, tridymite, and quartz, as the main non-clay minerals. Ferruginous beidellite and titanium minerals are also present in minor amounts. The halloysite-kaolinite ratio ranges from 75 to 25 to 100-0. Due to the alteration of very dense rocks, halloysite morphology is predominantly spheroidal. Tubular halloysite is the main constituent in more porous rocks, but the latter are scarce in the area. Because of the predominance of the spheroidal type, the use of halloysite as HNT (halloysite nanotube) is not feasible. Nonetheless, this mineral can be modified by different organic molecules, and used to remove pollutants such as emulsified hydrocarbons and heavy metals. A special product made with this halloysite is used as sunscreen when sprayed on fruits in areas of intense solar radiation. The whiteness of this mineral is not very high due to the amount of titanium oxide present in its composition (about 1%). Nevertheless, titanium oxide is present as individual particles, so it could be removed by a mechanical process. New applications for spheroidal halloysite are currently being investigated. Moreover, depending on the price and demand, the tubular halloysite of low grade deposits could be exploited.

Pozzolanic activity of calcined halloysite-rich kaolinitic clays

“…The additional water in the interlayers of halloysite has a decisive influence upon its crystal morphology, which is generally curled rather than platy form as occurred in kaolinite. Common forms are elongated tubes and spheroids (Cravero et al, 2016). For both morphologies different applications have been studied (Yuan et al, 2015;Fernández et al, 2015, Cravero et al, 2016.…”

The origin of spheroidal halloysites: a review of the literature

“…Churchman et al, (2016, this issue) report that spheroidal particles tended to have larger Fe contents, possibly including Fe oxyhydroxides, than tubular particles in mixtures. Spheroidal particles from Patagonia (Cravero et al, 2016) show that halloysite derived from different deposits had small Fe contents (0.5-1.5% in samples with 90-70% of halloysite), and there were no differences associated with different morphologies. The greater Fe values found in some localities are related to the presence of smectite associated with halloysite (from ∼3% up to ∼20% of Fe 2 O 3 , depending on the amount of smectite).…”

Optimum Calcination Condition of Waste Stabilized Adobe for Alkali Activated High Volume Adobe-Slag Binder Cured at Room Temperature

“…After finishing the mixing process in the required proportions according to each mix, the slump and flowability tests were conducted according to ASTM WK 63516 [30]. After that the fresh paste was cast into mold 50 mm × 50 mm × 50 mm and vibrated for 2 min on an electrical vibrating table.…”