Recovery of sawdust resulting from marble processing plants for future uses in high value-added products

The disposal of microfine marble sawdust contained in marble slurry waste, currently represents an additional economic burden for dimension stones companies. This is because the sawdust is considered less important in comparison with the crushed calcareous aggregate produced in stone processing plants. In addition, the sludge is mistakenly viewed as waste that has to be disposed of in landfill. State of the art in recovery and utilisation of calcareous sawdust is mainly aimed in uses as substitute for more expensive ingredient in the building sector. Moreover limestone dust, recovered from marble sawing and processing slurry, has not yet found real economically feasible industrial usage. Due to the high market value of micronised CaCO3, we study the use of limestone sawdust as functional filler in industrial products having higher added value, such as paper, rubber, paints, pharmaceuticals. Standard requirements of CaCO3 for this kind of products are very tight, especially those relating to purity level, particle size distribution and brightness. The high Calcium limestone deposit and the factories in Orosei Marble producing area (Sardinia, Italy) allow the production of high quality microfine dust. To evaluate the properties of the sawdust, several analysis were carried out to compare the results with the standard requirements of CaCO3 for paper, rubber and tyre production. The assessment concerns five different factories and it highlights the possible usage of the sawdust produced in Orosei by carrying out simple and inexpensive changes in both stone-working process and wastewater treatment. Finally, a commentary on environmental laws pertaining to the recycle of this kind of waste is also made in this paper.