Abstract:
Solvent extraction (SX) is a crucial technique in extractive metallurgy, particularly for recovering critical minerals used in renewable energy, electronics, and battery manufacturing. However, traditional SX relies on synthetic diluent (typically derived from petrochemicals) that could pose environmental risks due to their non-biodegradability. This study compares a bio-diluent (produced from biomass and fossil-derived source) as an alternative to conventional diluent for the recovery of cobalt and nickel.
The laboratory-scaled experiments investigated phase equilibrium analysis, metal extraction efficiency, and solvent stability assessments. Key performance metrics include extraction efficiency, selectivity, phase separation, and the analysis of total organic compounds (TOC) in the aqueous phase, after extraction.
The obtained experimental results clearly showed that for the experimental mixing setup, 0.05 mol/L P-based extractant in synthetic diluent in contact with aqueous phase at an A/O ratio of 1:1 reached equilibrium within 15 minutes. The pH isotherm indicates that optimal Co selectivity and extraction over Ni occur at pH 5.0–6.0 for both diluent systems. P1 achieves the highest Co extraction (~99.8%) with ~10.5% Ni co-extraction, while P2 and P3 show lower Co extraction and minimal Ni. Stripping studies of P1 with 0.1 mol/L mineral acid (MA) back-extract ~80% Co from the loaded organic in a single stage for both diluents. TOC analysis of the aqueous phase however reveals that the bio-diluent better stabilizes the P1 extractant, reducing organic (mainly P1) entrainment compared to the synthetic diluent.
Keywords: Solvent Extraction, Bio-diluent, Cobalt, Nickel, Extraction, Separation