CEReS Deliverable 4.2: Char PLS Treatment Unit Options

Work Package 4 Char Leaching aims to demonstrate the feasibility for utilisation of the acidic leachates (biolixiviant) generated from coal wastes bioleaching (Work Package 3) as leaching agent for extraction of the base and high-value metals contained in the char originating from the pyrolysis of PCB’s (Work Package 2). After metals being leached from the char and accumulate in pregnant leach solution (PLS), the next task is to extract metal(s) of interest and recover it to obtain a high-purity product.
Different from mineral ores, char (or pyrolyzed PCBs) contains various metals and elements, oftentimes in high grades. Most of the time, the leaching of the char is non-selective, meaning that other than metals of interest, the un-desired ones should also be dissolved at high concentration. This is proven to be problematic for recovery stage, thus highlight the importance of extraction stage as intermediate between leaching and recovery.
The solvent extraction stage consists of two steps; extraction step to transfer metal ions from solution (aqueous) to extractant (organic), and stripping step to transfer metal ions back from organic to aqueous. Concentrated metal ions in the aqueous phase are then transferred to recovery stage to produce metal product with high purity. This report will subsequently present the result on investigation of solvent extraction to produce concentrated electrolyte solution, followed by the result on recovery stage by electrowinning to produce metal product.