Quarry rehabilitation employing treated residual sludge from dimension stone working plant

Waste from stone and aggregate quarrying industry represents a serious environmental and economic problem in view of the difficulties related to its disposal, especially of the finest fraction. Although some attempts have been made to investigate possible reuse of these materials, little is known about their potential as components of a cultivation substrate. Their low physical and chemical fertility require the mixing with other materials to improve the general properties. The aim of this study was to evaluate if such a prospect product can be employed within the quarry for its environmental rehabilitation. Samples from gangue saw with abrasive shot (GSS), from diamond frame saw (DSS), and mixed sludge (MS)—from gangue and DSS—were collected and mixed with compost, green manure, and soil material. The resulting mixtures were further composted, distributed on parcels within the quarry area and sowed. The original materials and the mixtures were analyzed for metals and hydrocarbons (TPH) and for their phytotoxicity. The parcels were sampled and analyzed after 8 years. The results show that mixing with foreign materials can improve the overall quality and fertility of the sludge and that the mixture is not phytotoxic. Most metals concentrations decreased on mixing and further diminished after 8 years. TPH content was drastically reduced and fertility parameters tend toward equilibrium. This indicates that the residual sludge can be employed for quarrying rehabilitation after improvement of its fertility and of its environmental quality.