Effect of degree of substitution of carboxymethyl starch on diaspore depression in reverse flotation

Carboxymethyl starchs (CMS) with low and high degrees of substitution (CMSL and CMSH in short, respectively) were employed as depressants of diaspore in cationic reverse flotation using dodecylamine (DDA) as collector. The effect of degree of substitution of CMS on its depression performance was examined and the interaction mode and behavior were investigated in a comparative manner. Micro-flotation test showed that CMSL exhibited better performance in depressing diaspore than CMSH in a broad pH range. The adsorption of CMS on diaspore was studied by adsorption test, zeta potential measurement, and atomic force microscopy. It was found that CMSH corresponds to lower adsorption amount, thinner adsorption layer, and more negative charge than CMSL, resulting from the more chelating sites brought by the high degree of substitution. The surface tension measurement and DDA adsorption test further revealed that CMSL/DDA system gives a better depressing performance benefiting from the trapping effect by enveloping some DDA molecules inside the loop chains, while CMSH/DDA system is likely considered a quasi-surfactant.