# Interfacial Chemistry Involved in Selective Separation of NMC/LMO and LCO/LMO Binary Cathode Materials by Froth Flotation Using Oleic Acid

## TL;DR

This paper shows how froth flotation with oleic acid can efficiently separate different lithium-ion battery cathode materials, which is important for recycling.

## Contribution

The study reveals, for the first time, the mechanism of oleate adsorption on different cathode materials and validates froth flotation for selective separation.

## Key findings

- Flotation achieved 80% separation efficiency with >90% purity of NMC/LCO in a single stage.
- Oleic acid preferentially adsorbed on NMC and LCO surfaces via electrostatic interactions at pH 5.
- Separation efficiency declined at higher pH due to co-flotation of LMO materials.

## Abstract

The variability in cathode compositions
within recycled lithium-ion
battery (LIB) feedstocks poses a significant challenge to efficient
downstream refining processes. This study demonstrates the feasibility
of using froth flotation with oleic acid as a collector to selectively
separate lithium nickel-manganese-cobalt oxide (NMC) and lithium cobalt
oxide (LCO) from lithium manganese oxide (LMO) materials. Laboratory-scale
flotation tests achieved an 80% separation efficiency in a single
stage, producing a froth product with >90% purity of NMC/LCO at
approximately
90% yield. Concurrently, the LMO materials were enriched in the sink
product with ∼90% purity and ∼90% yield. This approach
was further validated using recycled cathode materials, confirming
its applicability to realistic feedstocks. The underlying mechanism
governing the selective separation of NMC/LCO from LMO was investigated
using ζ-potential measurements, contact angle measurements,
bubble-particle attachment experiments, and X-ray photoelectron spectroscopy
(XPS) analysis. Both contact angle and bubble-particle attachment
results confirmed that oleic acid adsorption rendered NMC and LCO
surfaces hydrophobic, thereby enhancing flotation recovery. At pH
5, oleic acid adsorbed preferentially onto NMC and LCO surfaces via
electrostatic interactions, while exhibiting minimal adsorption on
LMO surfaces. However, separation efficiency deteriorated at higher
pH, which was attributed to the co-flotation of LMO materials caused
by oleate chemisorption on MnOH+ species. This work establishes
froth flotation as a viable cathode/cathode separation strategy, providing
a low-cost, scalable pathway to preconcentrate and enrich nickel-rich
and cobalt-rich cathode active materials from incompatible cathode
chemistries for direct recycling or hydrometallurgical processing.
Furthermore, this study reveals, for the first time, the mechanism
of oleate adsorption on the surface of different cathode materials.