Sustainable enhancement of fine specularite recovery via selective flocculation with biopolymer-based carboxymethyl chitosan

Carboxymethyl chitosan (CMC), a macromolecular material with active hydroxyl and carboxyl groups, exhibits strong polarity and readily chelates with metal ions to form stable flocs. These properties make it a promising flocculant for recovering fine-grained iron oxide ores. In this study, CMCs with varying degrees of carboxymethyl substitution were synthesized to investigate their role in the magnetic separation of fine (−12.5 μm) specularite and quartz, focusing on the relationship between flocculation and selectivity. Under optimized conditions, CMC significantly enhanced the magnetic separation recovery of fine specularite by promoting selective flocculation, increasing recovery from 71.98 % to 93.74 %. In the specularite–quartz binary system, CMC selectively adsorbed onto specularite, inducing its aggregation while exhibiting minimal interaction with quartz. This selective aggregation improved magnetic separation performance, raising the iron grade and recovery of the magnetic concentrate by 2.1 % and 18.19 %, respectively. Fourier Transform Infrared Spectroscopy (FTIR) and molecular dynamics simulation (MDS) revealed that CMC’s carboxyl groups had a strong affinity for Fe atoms on the specularite surface, with adsorption energy nearly three times higher than on quartz. Sedimentation tests and polarized light microscopy confirmed that CMC promoted specularite aggregation via a bridging mechanism, increasing apparent particle size and improving separation efficiency. However, excessively long carbon chains sometimes entrapped quartz particles within specularite flocs, slightly reducing selectivity. These findings highlight CMC’s potential as an efficient, selective flocculant for fine iron oxide recovery and its broader applicability in mineral processing and related fields.