<p>The structure of non-polar groups in xanthate collectors, particularly carbon chain length, critically influences sulfide ore flotation performance. However, the microscopic adsorption mechanisms of xanthates with differing chain lengths on pyrite remain unclear. This study employs density functional theory (DFT) to investigate and compare the adsorption behavior of ethyl xanthate (EX) and butyl xanthate (BX) on pyrite surfaces. DFT calculations reveal that the binding energies of EX and BX with Fe²⁺ ions, as well as their adsorption energies on the pyrite surface, cannot be distinguished within the range of calculation error. This indicates that carbon chain length has minimal impact on the interaction strength of the polar head group. Crucially, however, the study uncovers that the lateral interactions between adsorbed xanthate molecules are strongly chain-length dependent. BX experiences less steric hindrance and exhibits significantly lower intermolecular repulsion energy than EX on the pyrite surface. Furthermore, solvation energy calculations demonstrate that BX possesses greater intrinsic hydrophobicity than EX. These computational insights reveal that the longer-chain xanthate’s superior flotation performance stems from reduced steric hindrance, lower intermolecular repulsion, and enhanced hydrophobicity, providing a molecular-level explanation for the observed differences. Subsequent experimental results corroborate these computational findings. More specifically, at pH = 8, when the concentration of butyl xanthate is 1 × 10^-4 mol/L, the recovery of pyrite using butyl xanthate is about 35% higher than that using ethyl xanthate.</p>