Upgrading of raw perlite by a dry magnetic technique

Abstract

Perlite of composition SiO2 73.6%, Al2O3 12.4%, Fe2O3 1.25%, MgO 0.15%, Na2O 2.99%, K2O 4.18%, H2O+ 3.17%, H2O- 0.2%, and found to contain 89.4% of amorphous phase and 10.6% of crystalline phase, the latter consisting of feldspars, biotite, quartz, magnetite and chlorite, was studied. Due to its largely amorphous nature, chemical composition and melting behaviour, perlite can be used in the manufacture of ceramics. For the glass industry, on the other hand, an impediment, albeit the only one, is the iron content, so that the iron-bearing minerals must be removed, which can be accomplished by dry magnetic separation. Laboratory and pilot-plant separation experiments carried out with these minerals showed that the Fe2O3 content cannot be reduced to below 0.65% owing to small inclusions of iron-bearing minerals that remain in the other minerals, or in the amorphous particles. Perlite with an Fe2O3 content below 0.7% and grain size of less than 1 mm can, however, be used in the production of coloured glass containers.