NaClO/NaOH soil oxidation for the remediation of two real heavy-metal and petroleum contaminated soils

•NaClO is more efficient than H2O2 or KMnO4 for oxidizing hydrocarbon contaminants.•NaClO is comparable to NaOH for dissolving soil organic matter.•In-situ generation of electrolytic NaClO minimizes the oxidation cost.•Sodium organic complexes limit the soil oxidation by NaClO.•Soil oxidation minimizes chelant loss.

The objective of this work is to develop a soil oxidation protocol for hydrocarbon and heavy metal remediation for real contaminated soils. The reagents were NaOH, NaClO, H2O2, KMnO4 or NaCl and electricity. Experiments used 25 g of soil in 50 ml of solution in a beaker or 50 g of soil in 200 ml of solution in a turbulent bed. Experiments in the beaker lasted 2 h to 4 d at 25 °C and used a 3-wt% oxidant solution at neutral pH. Experiments in the batch turbulent bed lasted 2 h to 4 d. An electrolytic cell converted a 5-wt% NaCl solution into a NaClO solution for these experiments. The work confirms that a well-tuned NaClO/NaOH protocol maximizes the contaminants' release. The work also confirms that NaClO is a more efficient oxidant than H2O2 or KMnO4 for hydrocarbon remediation. However, NaClO forms sodium-organic complexes, which limit the oxidation by NaClO if the pH stays neutral. Washing away or dissolving these complexes at high pH circumvents the limitation. A prolonged experiment with a continuous electrolytic NaClO generation also circumvents the limitation and lowers the oxidant cost. Overall, the work anticipates a scale-up procedure to degrade the soil organic matrix.