In contrast to Celite diatomaceous earth filter aids, which consist of almost pure silicic acid, Harborlite perlite filter aids are produced from volcanic obsidian rock by thermal expansion. Chemically, this is aluminium silicate which is almost as inert as silicic acid.
In terms of their structure, Harborlite perlite filter aids correspond to irregular fragments of spheres which do not have the same porosity as the intricate skeletons of the diatoms. Consequently, Harborlite perlite filter aids cannot be expected to produce the same degree of clarification with the same throughput as Celite diatomaceous filter aids. The benefits lie quite clearly in their cost-effectiveness: for instance, Harborlite perlite filter aids are more economical in the clarification of apple juice concentrate and are also free of cristobalite.
In three European plants, Celite Corp produces high-quality perlite grades using state-of-the-art processing methods that usefully supplement the diatomaceous earth range of filter aids.