Roles of solution chemistry and reagent–reagent interaction on carboxymethylcellulose adsorption onto graphite and implications on its floatability

Abstract

The influence of electrolytes (NaCl and CaCl2) and a copper sulphide collector (isopropyl ethyl thionocarbamate, IPETC) on adsorption of carboxymethylcellulose (CMC) onto a graphite surface were studied using adsorption tests, zeta potential measurements and floatability tests. Adsorption tests revealed negligible CMC adsorption in the absence of electrolytes and presence/absence of IPETC at lower CMC concentration of 0-100 mg/L, whereas CMC mild adsorption occurred at higher CMC concentration of 150-200 mg/L at pH 5.7 and 10. An increase in CMC adsorption was observed in the presence of electrolytes and their mixtures with IPETC. The CMC adsorption increased more in the presence of CaCl2 than NaCl, suggesting an effect of the cation valence. The addition of IPETC to NaCl solutions adversely affected the CMC adsorption and its effect was independent of the pH. Conversely, the addition of IPETC to CaCl2 solutions enhanced the CMC adsorption at pH 5.7, whereas it diminished at pH 10. The presence of electrolyte may induce the formation of complexes between CMC macromolecules with IPETC depending on the electrolyte type. Furthermore, CMC adsorption in presence of NaCl follows Langmuir isotherm whereas in presence of CaCl2 follows Freundlich isotherm. Moreover, the floatability tests indicated that the graphite floatability decreased more at pH 10 than at pH 5.7 in the presence of electrolytes. Only the floatability at pH 5.7 was comparable for both electrolytes. Finally, addition of IPETC to electrolyte solutions had a marked effect on graphite floatability. These findings have implications in copper sulphide flotation systems containing graphite as gangue in which IPETC is used as a collector and CMC as a depressant for graphite.