# Influence of Co-Occurring Heavy Metals on Cobalt Removal and Recovery from Wastewater by Continuous Flow In-Liquid Plasma Discharge Process

## TL;DR

This study explores a new method using plasma discharge to remove and recover cobalt from wastewater, but finds that other metals can significantly reduce its effectiveness.

## Contribution

The study introduces a continuous flow in-liquid plasma discharge system for cobalt removal and recovery, and quantifies the inhibitory effects of co-occurring metals.

## Key findings

- Multi-metal systems reduced cobalt removal efficiency by up to 91%.
- Copper had the strongest inhibitory effect on cobalt removal at equimolar levels.
- Recovered solids formed cobalt–metal oxide composites suitable for reuse.

## Abstract

Cobalt, a toxic heavy metal frequently present in wastewater, poses serious environmental and health risks but also represents a valuable resource for recovery. This study investigates a novel, environmentally friendly continuous flow in-liquid plasma discharge (CFILPD) system for simultaneous removal of cobalt, zinc, copper, and lead ions from aqueous solutions. The reactor contains two conductive channels where a stable plasma discharge forms between dielectric plates separating opposing electrodes, generating energetic electrons and hydroxyl radicals that react with dissolved metal ions. The effects of varying concentrations (5, 10, 50, and 100 ppm) of zinc, copper, and lead ions on the removal efficiency of 100 ppm cobalt ions were examined under constant conditions: 0.2 L/min argon flow rate, 200 W input power, and 50 mL/min liquid flow rate for 30 min. Results showed that increasing concentrations of co-existing metals significantly inhibited cobalt removal, with the largest reduction (91%) observed in multi-metal systems. Among individual metals at equimolar levels with cobalt, copper showed the strongest inhibitory effect (85% reduction), followed by zinc (53%) and lead (52%). Characterization of the recovered solids revealed cobalt–metal oxide composites (2.5–3 µm), suggesting their potential reuse in technological applications.