Comparative abiotic, regulatory-aligned assessment of nutrient and trace-metal release from secondary geomaterials for soil application

Abstract

Abstract This study provides an abiotic, regulatory-aligned leaching assessment of two secondary geomaterials intended for soil application: RE.WO, a secondary raw material derived from the thermal transformation of mineral wool construction waste, and BO50, a by-product of rock-cutting operations. The objective is to compare nutrient release and trace-metal mobility as a function of their contrasting compositions. To this aim, mineralogical and bulk-chemical characterization was combined with abiotic, time-resolved, regulatory-aligned in vitro leaching tests performed under weakly acidic, chelating, and weakly alkaline conditions. RE.WO is characterized by a fully amorphous glassy matrix that exhibits rapid dissolution kinetics and high cumulative cation release, particularly under chelating conditions. While this behaviour indicates higher short-term extractability of micronutrient elements (notably Mn, Cu, and Zn), it also facilitates the mobilization of regulated trace metals. Conversely, BO50 is dominated by crystalline silicates and K-bearing mineral phases; this refractory nature results in low solubility, gradual and sustained release of potassium and comparatively low mobilization of regulated trace elements under the tested conditions. These findings support a risk-informed approach to agronomic utilization. In terms of regulatory positioning under European Regulation 2019/1009, BO50 appears more readily compatible with possible classification as a virgin material or by-product, although conditional on verification of by-product status, registration under applicable chemicals legislation, and compliance with contaminant requirements. Conversely, the higher mobilization of regulated trace elements in RE.WO may preclude its current classification under European Regulation 2019/1009 pathways and its use appears more defensible in restricted non-food applications.