Abstract:Carboxymethyl starchs (CMS) with low and high degrees of substitution (CMS_L and CMS_H 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 CMS_L exhibited better performance in depressing diaspore than CMS_H 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 CMS_H corresponds to lower adsorption amount, thinner adsorption layer, and more negative charge than CMS_L, resulting from the more chelating sites brought by the high degree of substitution. The surface tension measurement  and DDA adsorption test further revealed that CMS_L/DDA system gives a better depressing performance benefiting from the  trapping effect by enveloping some DDA molecules inside the loop chains, while CMS_H/DDA system is likely considered a quasi-surfactant.

Key words: carboxymethyl starch; diaspore; reverse flotation; depressant