Suitability of Greek perlite for industrial applications

Synopsis Perlite from the Greek islands of Milos, Kimolos and Kos is compositionally a calc-alkaline rhyolite that consists principally of glass (>85%) with mi nor amounts of phenocrysts. Different textural types can be recognized with varying degrees of vesicularity, including a classical perlite with sphero idal fractures of 'onion-skin' type. A wide variety of samples were expanded in a laboratory furnace and the bul k density and other properties relevant to the uses of the expanded materia l were determined. Only a small amount of non-expanded material remained af ter heating. The bulk density of the expanded perlite covers a broad range, from 25 to 230 kg/m(3), and is partly dependent on the size of the feed. T he compaction resistance is variable, but high oil absorption (400-2200 ml/ 100 g) and specific surface area (6-13 m(2)/g) are obtained. These properti es appear to be independent of the bulk density. It appears that the expans ion characteristics are more dependent on furnace conditions than on any mi nor variations between the perlite types. Once expanded, the product lends itself to most perlite applications. The c oarser expanded material from Miles is best suited for concrete, plaster an d horticulture. The lowest-density expanded perlite from all three islands is suitable for loose-fill insulation applications and the finer fractions are appropriate for cryogenic, filter-aid and filler purposes. Kimolos expa nded perlite is probably best suited for the animal feed and thermal insula tion markets.