LigniOx Lignins - Sustainable Depressants for Froth Flotation in Mineral Processing

Froth flotation is a widely used technology in the mining industry to enrich valuable minerals for further processing. To aid the separation of high value minerals from lower value minerals, depressants and collectors can be added to adjust the enriched components. Sulfidic minerals, such as chalcopyrite (CuFeS2), are one of the main sources of copper, zinc, and lead. However, the most abundant sulfidic mineral pyrite (FeS2) has low economic value and is closely associated with these minerals. In flotation, depressant are commonly used to separate pyrite. Currently, the depressants used for pyrite separation are inorganic compounds, such as cyanide. These compounds can be toxic and harmful for the environment and new sustainable and environmentally friendly depressants are needed. Recently, an alkali-O2 oxidation (LigniOx) process for producing lignin dispersants from different lignin by-streams, such as kraft, organosolv, and hydrolysis lignin, has been introduced. These anionic LigniOx lignins have high potential to serve as depressing agents in froth flotation.

To investigate the depressant potential of four LigniOx lignins, pyrite-adsorption tests were conducted under different pH conditions. All the LigniOx lignins adsorbed on the pyrite surface. Organosolv lignin based LigniOx (LigniOx-OSL) had the highest adsorption. In addition, it was observed that increase in pH decreased the adsorption of all lignins. Presumably, it was because the mineral surface become negatively charged at high pH causing repulsion to the anionic lignin. Adsorption experiments of LigniOx-OSL to chalcopyrite with or without a collector were performed. LigniOx-OSL did not adsorb on chalcopyrite to the same degree as on pyrite. Furthermore, the presence of a collector decreased the adsorption of LigniOx -OSL. The results are promising and the work will be carried on with further flotation experiments.