Optimizing biological and physicochemical properties of acidic mine tailings through combined organo-mineral amendments and topsoil application

This study aimed to evaluate the effect of application of soil material from topsoil and different doses of marble sludge (MBS) and sheep manure (SM) on physicochemical and biological properties of acidic Kettara mine tailings.

Two main mixtures were prepared: M1—70:30 ratio of mine tailings (MT) to soil material from topsoil (TS) with 10% MBS; M2—60:40 ratio of MT to TS with 6% MBS. Both mixtures received SM treatment at doses ranging from 4 to 12%.

The application of TS and MBS significantly increased the pH of MT (from 2.11 to 7.54), while reducing the EC (from 7.86 mS cm⁻¹ to 2.74 mS cm⁻¹). The addition of the organic amendment increased the organic carbon, total nitrogen and P availability in all treatments. Data also indicated that organo-mineral amendments efficiently reduced CaCl₂- exchangeable Pb, Cu (1.7–two fold), and Zn (33 fold) if compared to the untreated MT. The improvement of physicochemical properties of MT resulted in an increase in soil microbial abundance and in the activity of urease, dehydrogenase, and alkaline phosphatase. Moreover, the addition of 10 and 12% of SM to M1 and M2 significantly increased seedlings’ root length (2- 2.5 fold) compared to the treatments without SM. A remarkable increase was observed in Peganum harmala L. root length (60–73%) if compared to Lollium perenne.

Overall, the treatment containing M2 and 10% of sheep manure was the most effective treatment suggesting its efficient use for the restoration of contaminated mining sites.