Research Of Adsorption Of Starch And Its Derivatives Onto The Surface Of Diaspore

Starch and its derivatives have been extensively used as depressants in the field of minerals engineering, where they fulfill their roles mainly by being adsorbed on the solid surface. In this thesis, the adsorption thermodynamics and kinetics of five types of modified starches, which could be classified as non-ionic starches (soluble starch, abbreviated as SS; highly branched waxy maize starch, WMS) and ionic starches (cationic starch, CAS; carboxymethyl starch, CMS; amphoteric starch, AMS), onto diaspore were investigated through static adsorption experiments, accompanied by varying the pH values and the absence/presence of the cationic collector (dodecylamine, DDA). The expected results would be conducive to gaining a better understanding on the mechanism of adsorption of starches on minerals.In pH tests, it was found that, the adsorbance of WMS, SS and CMS decreased with the increase of pH, in sharp contrast to the opposite trend observed for CAS. Interestingly, pH variation had seemingly few effects on the AMS system, which might be due to its amphoteric feature. It was found that in all cases the adsorption behaviors can be best described according to the pseudo-second-order kinetic equation. Based on the analysis of the obtained activation energy, it was suggested that the adsorption of WMS (38.143kJ·mol-1) and CMS (41.214kJ·mol-1) onto diaspore with higher energy level exhibited partial chemical adsorption characteristics, while that of SS (28.59kJ·mol-1), CAS (15.11kJ-mol-1) and AMS (25.594kJ-mol-1) was mainly due to physical adsorption. The linear fit analysis of the thermodynamic data showed that the adsorption of WMS, CMS and AMS on diaspore was well consistent with Langumir model, which was further in principle supported by the reasonable match between modeled and observed adsorption capacity. On the other hand, in the case of SS and CAS, the Freundlich equation led to a better fitting. The adsorption enthalpies changes evidenced the presence of hydrogen bonding (8-50kJ-mol-1) between mineral and starches. It was further revealed by the thermodynamic analysis and activation energy calculation that the adsorption of WMS and CMS onto diaspore was a spontaneous, endothermic, and entropy driven process, which should involve both physical and chemical adsorption. In contrast, the adsorption of SS, CAS and AMS on diaspore was also a spontaneous but exothermic and enthalpy driven process, which can be treated as physical adsorption.In the presence of cationic collector DDA, it was noticed that the adsorbance of starches changed more or less. The fluorescence spectroscopy together with the adsorbance determination helped to figure out the role of the pre-adsorption of DDA in the relocation of interaction sites as well as the redistribution of surface charge of particles. Furthermore, the synergy effects between DDA and starches, whether of anionic or cationic type, during the interaction were fundamentally established, which largely relied on the structural feature and charge level of starches. In this respect, CMS exhibited the strongest interaction with DDA.