Flotation-Based Separation Method for the Remediation of Marine Sediments Contaminated by Mining and Metallurgical Wastes

Marine sediments contaminated by mining and metallurgical activities represent a major environmental challenge, particularly in industrial port areas. This study develops and evaluates a characterisation-driven flotation flowsheet for contaminated marine sediments from the industrial harbour of Portovesme (southwestern of Sardinia, Italy). The novel contribution lies in integrating sediment mineralogical and particle-size characteristics into the arrangement of classification and sequential flotation stages, while evaluating process performance in terms of regulatory compliance, sediment recovery, and minimisation of contaminated residues rather than removal alone. Batch flotation tests were based on a conventional sphalerite flotation scheme, without a comminution stage. Three alternative process configurations were investigated by varying the position of two particle-size classification steps. The selected configuration was subsequently applied to sediments with different contamination characteristics, for a total of five treatment tests. Four of the five tests produced a decontaminated product (DP) with Zn, Pb, Cd, and Hg concentrations below the Italian regulatory thresholds for industrial sites (CTC_B). Approximately 75%–85% of the treated sediment was recovered as DP, while 15%–25% was concentrated into a non-decontaminated product (NDP). Contaminant removal efficiencies reached approximately 75% for Pb, 82% for Zn and 90% for Cd and Hg. These findings support the potential of characterisation-driven flowsheet design to recover sediments potentially suitable for beneficial reuse while concentrating contaminants into a smaller residual fraction.