Amine-modified Cyanex 272 as a next-generation green extractant for selective cobalt recovery from nickel-rich industrial refinery streams

The growing demand for cobalt in battery and alloy production has intensified the need for efficient and sustainable recovery methods from complex refinery streams. Conventionally saponified Cyanex 272 systems require stringent pH control and continuous ammonia dosing, creating operational and environmental challenges. To address these limitations, this study introduces a novel approach using amine-modified Cyanex 272 for selective cobalt extraction. Unlike previous work focused on saponification, this research demonstrates the first application of butyl- and hexyl-modified Cyanex 272 ([C 4 H 9 NH 2 ][Cyanex 272] and [C 6 H 13 NH 2 ][Cyanex 272]) in real refinery liquors containing 1.9 g/L Ni, 0.53 g/L Co, and 436 g/L (NH₄)₂SO₄ at pH 6.5. FT-IR and NMR analyses confirmed successful modification of the extractants. Results revealed that the butylamine-modified system achieved near-complete cobalt extraction (up to 99.9%) at concentrations as low as 1.5% v/v, while limiting nickel co-extraction to below 6%, even under unfavorable Ni/Co ratios. The modified extractants maintained stable performance across a wide pH and temperature range, reducing ammonia dependency and improving phase stability. Thermodynamic analysis indicated that cobalt uptake is endothermic and entropy-driven, explaining enhanced selectivity at elevated temperatures. Stripping studies further confirmed efficient cobalt recovery (>99%), a novel, environmentally responsible solution for sustainable cobalt extraction from complex refinery streams.