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UBC Theses and Dissertations

The role of mineral surface composition and hydrophobicity in polysaccharide/mineral interactions Liu, Qi


The interactions of polysaccharides (dextrin, amylopectin and carboxymethyl cellulose (CMC)) with variously modified quartz samples were investigated using floatability, wettability, electrokinetic and adsorption tests, supplemented by conventional titration and infrared spectroscopic studies. The quartz samples were treated either by methylation (rendered hydrophobic), lead coating (introduction of metallic adsorption centres), or both forms of surface modification. The presence of metal ionic sites on a quartz surface played a decisive role in polysaccharide adsorption. The adsorption densities of both dextrin and CMC on lead-coated quartz were both much higher and much more pH-dependent than those on uncoated quartz. The "hydrophobic bonding" of dextrin with mineral surfaces as reported in the literature was not observed with hydrophobic (methylated) quartz. However, if the quartz contained surface lead ionic sites and was also methylated, it adsorbed more dextrin than unmethylated, lead-coated quartz. This was also true for the adsorption of CMC onto similarly modified quartz samples. To obtain a rational understanding of the importance of metal ions in polysaccharide adsorption, studies of the solution chemistry of polysaccharides and metal ions were conducted. CMC co-precipitated with both metal cations and metal hydroxy complexes, (including metal hydroxides), whereas dextrin co-precipitated only with metal hydroxides. Co-precipitation involving either polysaccharide caused a decrease in the solution pH. Dextrin-metal co-precipitation occurred at pH optima of 7.5, 8, 9, 11, and 12 for ferric, aluminum, cupric, lead and magnesium ions, respectively. Infrared spectroscopic studies of the precipitates revealed the elimination of glucose ring deformation, suggesting a chemical basis for the interaction between dextrin and metal hydroxides. The surfaces of sulphide minerals behaved like hydroxide during dextrin adsorption. Since copper and lead hydroxides form over different pH ranges, the pH ranges for optimum adsorption of dextrin on copper sulphides and lead sulphides were different. The results of preliminary flotation tests indicated that dextrin could be utilized in the differential flotation of Cu-Pb sulphides. Small scale flotation tests conducted on synthetic mixtures of chalcopyrite and galena confirmed this point.

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