Comparative efficacy of electrokinetic and static leaching for selective metal recovery and nutrient release from porphyry Cu tailings

This study presents the first systematic comparison of electrokinetic (EK)-assisted and static leaching (SL) for the selective extraction of Cu from porphyry Cu tailings, while also assessing the potential biotoxicity and nutrient release within treated residues. Twelve lixiviants were tested, comprising: inorganic acids, organic acids, chloride solutions and deep eutectic solvents (DES). EK consistently enhanced metal leaching due to the additional mass transfer under a superimposed voltage gradient. Citric acid (0.5 M) proved most effective, achieving 60.8% Cu recovery with EK (2 V/cm) over 22 days, compared to 41.9% with SL. EK also markedly improved DES performance; CaCl₂:ethylene glycol achieved a 25-fold increase in Cu recovery (17.6% vs. 0.7% for SL), demonstrating that EK can substantially mitigate mass-transfer constraints in such viscous solvents. Principal Component Analysis showed greater variability under EK, indicating lixiviant-specific amplification of leaching efficacy. Whilst EK-assisted leaching increased the concentration of actually bioavailable toxic metals within treated residues, suggesting short-term ecological risks if such metals are not effectively captured, it simultaneously increased the bioavailability of plant-available nutrients: Fe, K, Mg and P, whilst also substantially decreasing the total potentially bioavailable concentration for all metals. Overall, these findings show that EK-assisted leaching, particularly when combined with citric acid, offers a potentially transformative approach for target metal recovery from porphyry Cu tailings whilst also lowering their total potential long-term ecological impact and enhancing nutrient availability.