Implementation of Indirect Heating Technology Towards The Production of Expanded Microspheres from Low Value Pitchstone Fines
Pitchstone is a natural occurring volcanic rock that mainly consists of amorphous silica and low amounts of other metal oxides. Its chemical composition and structure is similar to that of perlite and obsidian; the main difference between these materials constitutes their content in chemically bound water. Perlite water content ranges between 2 and 5% and constitutes a well-known raw material for the production of cellular, lightweight particles. Pitchstone’s water content exceeds that of perlite and its direct expansion with traditional expansion equipment is practically impossible. Thus prior partial removal of its water content constitutes a prerequisite towards the production of acceptable expanded material. Nevertheless, even in case of raw material preparation, its expansion to traditional furnaces is cumbersome when its granulometry is below 500 μm. In the current research work a recently developed perlite expansion process is applied for the production of expanded glassy microspheres from low-values pitchstone ore. Two different production routes were applied: (1) the ore was dried prior to the expansion in order to partially reduce its water content one and afterwards was subjected to thermal processing in a Vertical Electrical Furnace (VEF) for the production of expanded, glassy microspheres, and (2) the raw material was introduced directly in the VEF and both drying and expansion were performed at a single step process. It was found that the new method is capable to produce expanded, glassy microspheres with loose bulk density below 110 kg•m-3, even without excessive water removal prior to expansion. SEM morphological analyses shown that the produced grades are cellular, closed-structured, and exhibit low porosity. Furthermore, according to the expansibility test that was performed to the produced grades, theircontent in sufficiently expanded grains exceeds 88 % vol. For the first time in bibliography, the novel VEF method has been successfully applied for the production of closed-structure expanded, glassy microspheres from pitchstone fine grade. The promising experimental results of the current preliminary study possesses with an alternative route towards the valorization of pitchstone fines that nowadays constitute an abundant waste of non-economic value. The expanded microspheres produced may find various potential applications including their use as filler in plastics or paintings, or in joint compounds.
Index Terms- pitchstone fines expansion, vertical electrical furnace, lightweight microspheres, wastes valorization.