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Advantages and Limitations

While recycling of fillers sounds to be sensible and straightforward, there are many hurdles to be overcome if it is to be a commercial success and this is why it is still in its infancy today.

First we must consider availability, security, and consistency of supply. These can all be serious problems for waste and by-product materials. The principal fillers used in volume applications (greater than 500,000 tons worldwide) are presented in Table 2. They all have specific characteristics which make them difficult to substitute by other powders and the main sources of recycled powders that might be used as fillers do not fit these requirements very well. As an example, most by-product powders (glass, fly ash, rice husks) have high hardness, while polymer-processing equipment for most of the bulk fillers (carbonates, talc ) is designed around their relatively low hardness and would not be suitable. As a result, we currently see little up or down-cycling of other products into filler applications, with the main emphasis being on recycling of existing fillers.

Next is cost. Many of the bulk particulate fillers are relatively low in cost. The raw materials are essentially free, and the production costs are those involved in extraction, beneficiation (purification), and size modification. These costs are not dissimilar to that for an equivalent recyclate which must bear collection, separation, purification, and possibly size reduction costs. As a result, they can be similar to or even higher in price than the virgin product.

Finally, one must consider competition from alternative uses for the powder. This is particularly felt with many silica waste powders, which often find more lucrative applications in areas such as cement, for instance.

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