From waste to solution: Valorisation of a dolomite by-product for degraded soil rehabilitation

Acidic, metal(loid)-contaminated soils require scalable circular solutions; the efficacy of a finely milled dolomite by-product, alone or co-applied with vermicompost (VC) or biochar (B), was assessed as amendments to rehabilitate an Iberian mine-impacted soil and to enable phytostabilisation with Lolium multiflorum. In a greenhouse pot trial comparing five amended treatments (SD, SV, SB, SVD, SBD) against an unamended control, soil chemistry (pH, C/N, available P, CEC, Al saturation), TCLP-extractable Cu-Zn-As, plant biomass, and multivariate response (PCA) were quantified. Dolomite sharply neutralised acidity (pH 3.1 → 8.3-8.5), increased CEC (23.0 → 65.5-81.9 cmol₍₊₎/kg), and reduced Al saturation (11.2 % → ∼0.02 %), with large decreases in TCLP-Cu fell to <10 mg/kg in dolomite-containing treatments and to <3 mg/kg with VC formulations; Zn was suppressed to <65 mg/kg except where liming counteracted B effects. Arsenic showed a distinct pattern: VC increased TCLP-As in close association with available P, whereas dolomite alone or with B kept As below detection-most plausibly via Ca/Mg-driven (co)precipitation of sparingly soluble arsenate/phosphate phases; notably, SVD < SV for As, indicating partial mitigation by dolomite. Vegetation failed in the control but established across all amended soils, with biomass maximized under VC. Overall, the results indicate that dolomite by-product particularly in combination with VC provides a circular, field-relevant route to restore soil function and reduce bioavailable Cu and Zn by >90 % while sustaining plant establishment; given VC-linked As mobilization, co-amendment with Fe-rich sorbents and prudent P management are recommended to minimize risk in practical applications.