Pilot-scale counter-current acid leaching process for Cu,Pb, Sb,and Zn from small-arms shooting range soil

Purpose

The main objective of this study was to evaluate the potential of a counter-current leaching process (CCLP) on 14 cycles with leachate treatment at the pilot scale for Pb, Cu, Sb, and Zn removal from the soil of a Canadian small-arms shooting range.

Materials and methods

The metal concentrations in the contaminated soil were 904?±?112 mg Cu kg^–1, 8,550?±?940 mg Pb kg^–1, 370?±?26 mg Sb kg^–1, and 169?±?14 mg Zn kg^–1. The CCLP includes three acid leaching steps (0.125 M H₂SO₄?+?4 M NaCl, pulp density (PD)?=?10 %, t?=?1 h, T?=?20 °C, total volume?=?20 L). The leachate treatment was performed using metal precipitation with a 5-M NaOH solution. The treated effluent was reused for the next metal leaching steps.

Results and discussion

The average metal removal yields were 80.9?±?2.3 % of Cu, 94.5?±?0.7 % of Pb, 51.1?±?4.8 % of Sb, and 43.9?±?3.9 % of Zn. Compared to a conventional leaching process, the CCLP allows a significant economy of water (24,500 L water per ton of soil), sulfuric acid (133 L H₂SO₄ t^–1), NaCl (6,310 kg NaCl t^–1), and NaOH (225 kg NaOH t^–1). This corresponds to 82 %, 65 %, 90 %, and 75 % of reduction, respectively. The Toxicity Characteristic Leaching Procedure test, which was applied on the remediated soil, demonstrated a large decrease of the lead availability (0.8 mg Pb L^–1) in comparison to the untreated soil (142 mg Pb L^–1). The estimated total cost of this soil remediation process is 267 US$ t^–1.

Conclusions

The CCLP process allows high removal yields for Pb and Cu and a significant reduction in water and chemical consumption. Further work should examine the extraction of Sb from small-arms shooting range.