Exploitation of mineral waste fine fraction to produce substrates to use for land rehabilitation

Waste coming from construction and demolition activities (C&DW) and rock and soil from excavation works (RSE), together with waste coming from mining and quarry industry, represent the 1st and the 2nd source of waste production at EU level (36 and 25% respectively, Eurostat 2019 – data 2016). They can cause serious environmental and economic problems in view of the difficulties related to their disposal, especially in the case of the finest fraction. At present, little is known about their potential as constituents of a cultivation substrate. Indeed, they are characterized by an inappropriate structure and a low chemical fertility, requiring them to be mixed with organic materials to improve their general properties. The aim of this study were to test the agronomic characteristics of the produced mixes in order to evaluate their potentiality to be used for land rehabilitation. The investigated mineral wastes (fine fraction) were: residual sludge from ornamental stones working activity, sludge coming from aggregates production, tailings and waste rock fine fraction from mining activity (Zn-Pb and Ni closed mines), fine fraction connected to C&DW and RSE recycling activities. These waste materials were collected and mixed with compost, shredded green compounds, wastewater sludge and soil material. The original materials and the mixtures were analyzed for metals and hydrocarbons (TPH, where present) and for their phytotoxicity (seed germination and plants growing). The results show that mixing with organic compounds can improve the overall quality and fertility of the mineral waste fine fraction and that the mixture is not phytotoxic. This indicates that the mineral waste fine fraction could be employed, when properly managed and treated, for land rehabilitation after improvement of its fertility and of its environmental quality.