Application of exopolysaccharide directionally synthesized by Xanthomonas campestris as the green selective depressant for the clean flotation of talc: Statistical optimization and mechanism analysis

Abstract

During froth flotation, the more non-polar, friable talc (Mg3(Si2O5)2(OH)2) usually adheres to the surface of sulfide ore and floats up, causing difficulties in flotation separation and subsequent industrial treatment. Microbial flotation as a green separation method avoids chemical contamination due to the limited selectivity and high agent consumption of the currently used inhibitors. Recent studies have found that exopolysaccharides produced by Xanthomonas campestris (X.c) could be used as inhibitors for the efficient flotation separation of talc from chalcopyrite. Therefore, this paper is the first attempt to optimize the molecular structure of exopolysaccharides and the optimal culture parameters of this strain to synthesize a green depressant for efficient flotation of talc, and also to explore in depth the mechanism of its selective inhibition of talc. Results of fermentation condition experiments and Fourier transform infrared analysis showed that the exopolysaccharides with the presence of polar groups (—OH and –COOH) significantly inhibited the floatability of talc. 1H Nuclear magnetic resonance further identified the active components of polar groups in the polysaccharide structure as hydroxyl groups, glucuronic acid, and pyruvic acid. Furthermore, the fermentation parameters were optimized by response surface methodology and increased the yield of exopolysaccharides by 5.55 g/L compared with before optimization. Flotation experiments on mixed ore confirmed the excellent selective inhibition of the synthesized exopolysaccharide at pH 7 and a 60 mg/L concentration. The contact angle test showed a significant decrease from 65.04° to 51.77° on the talc surface after the reaction with 60 mg/L concentration of exopolysaccharides. Atomic force microscopy characterization directly revealed the multilayer adsorption of exopolysaccharides on the talc surface, as well as a high coverage of 50.88%.