Comparative Flotation Performance of Amine Collectors with Different Alkyl Chain Lengths for Efficient Separation of Quartz from Mica and Feldspar

The reverse flotation separation of high-purity quartz from mica and feldspar is strongly governed by the molecular structure of cationic collectors, particularly their carbon chain length. In this study, the flotation behavior of quartz, mica, and feldspar was systematically investigated using cationic collectors with different alkyl chain lengths through micro-flotation experiments and actual mineral flotation tests. Flotation results demonstrate that short-chain collectors effectively suppress quartz flotation while preferentially floating impurity minerals, whereas excessive carbon chain length leads to non-selective adsorption and increased quartz recovery. Zeta potential measurements reveal that increasing carbon chain length enhances collector adsorption on all mineral surfaces, thereby reducing surface charge differences and flotation selectivity. FTIR analyses verify the evolution of adsorption behavior from selective electrostatic interaction to hydrophobic-dominated, non-selective adsorption with increasing chain length. DFT calculations show that collector-mineral interactions are strongly mineral-dependent: adsorption strength increases with carbon chain length on mica, decreases on quartz, and exhibits a non-monotonic trend on feldspar. Notably, collectors with short carbon chain length produce the largest adsorption energy contrast between impurity minerals and quartz, accounting for the optimal reverse flotation selectivity. This work provides a multi-scale mechanistic understanding of how carbon chain length regulates collector–mineral interactions and offers theoretical guidance for the rational design of cationic collectors for high-purity quartz flotation.