Caustic-digested starch and its adsorption on hematite

Adsorption characteristics on hematite of caustic-digested starch by sodium hydroxide or potassium hydroxide were investigated through a series of tests, like adsorption tests, paste titration and zeta potentials measurement, scanning electron microscope measurement (SEM) and Fourier transform infrared spectroscopic analysis (FTIR) as well. An attempt was made in order to identify the possible effects of starch digested with alkali at different concentrations on its adsorption on mineral surfaces. All results pointed out that a different amount of carboxyl groups in the starch gel were harvested from alkali-digestion as a function of concentrations of sodium hydroxide or potassium hydroxide; more acidic groups were produced if higher concentrations of alkali were added. These carboxyl groups may contribute the acid/base interaction of the caustic-digested starch on hematite. Also, different concentrations of sodium hydroxide to digest starch seem to induce different degrees of its gelatinization from the SEM results, partially attributing to a wide range of its adsorption capacities on mineral surfaces. The optimum adsorption density of the caustic-digested starch on mineral surfaces, 9.87 mg/g hematite for sodium hydroxide and 10.51 mg/g hematite for potassium hydroxide, respectively, was achieved at the weight ratio of starch to sodium/potassium hydroxide as 1:2.