Immobilization of Pb in calcite–dolomite flotation tailings used as a concrete additive

The mining industry faces increasing demand for raw materials and stringent environmental regulations imposed by the European Union. These constraints promote the development of technologies that enable the reuse of industrial waste. Such approaches are consistent with the principles of the circular economy, which emphasize recycling and material recovery. The use of industrial by-products as partial substitutes for natural raw materials is well established in the construction sector.

Carbonate-rich flotation tailings from the Zn–Pb mining industry can partially replace sand in cement mortars. This study aimed to evaluate methods for limiting Pb release during the weathering of mortars containing such material as additive. In the experiments, cement mortars were prepared with 32 wt% of quartz sand replaced by flotation tailings from a Zn–Pb ore-processing plant. Two immobilization strategies were tested:

• Addition of phosphate ions (PO₄³⁻) utilizing Phosphate-Induced Metal Stabilization (PIMS), based on in situ precipitation of the low-solubility phase pyromorphite, Pb₅(PO₄)₃
• Amendment with natural zeolite (clinoptilolite) as a sorbent with a high affinity for Pb.

Mortars were prepared in accordance with EN 196-1. Two compositions were investigated:
(i) mortar containing flotation tailings, Portland cement (CEM I 52.5 N), and water enriched in PO₄³⁻ and Cl⁻;
(ii) mortar containing flotation tailings and clinoptilolite, with 20 wt% of the cement replaced by zeolite, mixed with deionized water.

After curing for 28 days, leaching tests were performed following PN-EN 12457-2:2006.

Phosphate addition did not reduce Pb mobility. The leached Pb concentration was at the order of 0.8 mg kg⁻¹, identical to that of the reference mortar without immobilizing additives. In contrast, zeolite amendment was fully effective. Lead concentrations in the leachate were below the detection limit (~0.05 mg L⁻¹).

These results demonstrate that cement mortars incorporating Zn–Pb flotation tailings can be produced with effective immobilization of Pb by minor additions of clinoptilolite. Further studies are required to optimize zeolite content with respect to the mechanical properties of the mortar. This approach offers a promising pathway for reducing mining waste and conserving natural mineral resources.