The effectiveness of a quicklime-based treatment on reducing the mobility of heavy metals (lead, chromium, arsenic and mercury) in contaminated soils was evaluated using both slurry batch-contact and optimum water content compaction experimental techniques. The results indicated that lead, arsenic and trivalent chromium leachabilities were significantly reduced as a result of the quicklime treatment, while at the same time significant strength gains were evidenced for the treated soils. However, more hexavalent chromium was released from lime treated mixes than from the untreated solid due to the low adsorption and high solubility of chromate at high pHs. The results obtained from pH-controlled extraction, x-ray diffraction and scanning electron microscopy suggested that a significant portion of the immobilized heavy metals are strongly associated with pozzolanic reaction products.