Abstract: Apatite is a crucial mineral resource for phosphorus extraction.The significant differences in the flotation be havior of different particle sizes seriously constrain the separation efficiency in flotation separation process.To address this is sue,this study systematically investigated the selective inhibition behavior and mechanism of sodium lignosulfonate (LS-Na) through pure and artificial mixed mineral flotation tests conducted on sized fractions of apatite and calcite (its primary associat ed gangue mineral).Under natural pH conditions using a BO collector (dosage of 2 kg/t),LS-Na effectively separated apatite from calcite,with its inhibition efficacy showing a significant particle size dependence.The strongest inhibition was observed for the coarse fraction (0.3~0.074 mm),where merely 20 mg/L of LS-Na resulted in a recovery difference exceeding 70%.As the particle size decreased to medium (0.074~0.023 mm) and fine (-0.023 mm) fractions,the required LS-Na dosage for effective separation increased,yielding recovery differences of approximately 60% and 20%,respectively.Mechanism studies revealed that the adsorption of LS-Na was much stronger on the calcite surface than on the apatite surface,which significantly reduced the hydrophobicity of calcite (contact angle decreased from 112.1° to 17.5°) while having a lesser effect on apatite (decreased from 110.3° to 84.9°).Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed that chemisorption,primarily through the —SO 3 functional groups of LS-Na,occurred on both mineral surfaces.However,the Ca2+ sites on the calcite surface facilitated more stable chemical bonding with —SO 3 ,leading to the preferential and stronger adsorption of LS-Na onto calcite and thereby achieving selective inhibition.This research provides a theoretical basis for the ap plication of sodium lignosulfonate in mineral flotation,particularly in the separation of calcium-containing minerals.

Key words: sodium lignosulfonate,flotation,depressant,apatite,calcite,classification