Cleaner production of potassium sulfate from salt lake ore: mechanism of selective flotation and closed-loop conversion of glaserite

SDS outperforms amine collectors in glaserite flotation. • SDS chemisorbs on glaserite; OA only physisorbs. • Phase diagram guides closed-loop glaserite-to-K 2 SO 4 conversion. • Dual recycling loops maximize resource use and atom economy. • Sustainable route for salt lake potassium sulfate production. The efficient recovery of glaserite (Na 2 SO 4 ·3K 2 SO 4 ) from salt lake ores and its subsequent conversion to potassium sulfate (K 2 SO 4 ) is crucial for sustainable potash fertilizer production. This study investigates the selective flotation separation of glaserite from sodium sulfate (Na 2 SO 4 ) using sodium dodecyl sulfate (SDS) and octadecylamine (OA) as collectors, and further develops a closed-loop chemical conversion process guided by phase diagram analysis. Micro-flotation tests show that SDS achieves a superior glaserite recovery of 82.4% at a dosage of 120 g/t, significantly outperforming OA (67.7%), while neither collector effectively floats sodium sulfate. Multi-spectral (FTIR) and zeta potential analyses, combined with density functional theory (DFT) calculations, reveal that SDS undergoes strong chemisorption on glaserite surfaces via its sulfonate group with a high adsorption energy of −175.71 kcal/mol, increasing the water contact angle from 32.22° to 63.41°. In contrast, OA exhibits weaker physical adsorption (−33.39 kcal/mol), providing only moderate hydrophobization. Based on the 25 °C phase diagrams of the K + , Na + // Cl⁻, SO 4 2 ⁻–H 2 O quaternary system and the NaCl–KCl–H 2 O ternary system, a closed-loop process was designed comprising three steps: (1) reaction of KCl with glaserite to precipitate K 2 SO 4 ; (2) addition of Na 2 SO 4 to the mother liquor to precipitate glaserite; and (3) removal of residual SO 4 2 ⁻ with CaCl 2 followed by evaporative crystallization of NaCl, with the final mother liquor recycled. Theoretical calculations based on 100  kg KCl yield 154.00  kg K 2 SO 4 , 65  kg glaserite, and 15.3  kg NaCl, with experimental deviations within 3%. The obtained K 2 SO 4 and NaCl purities reach 98.90% and 99.5%. The one‑pass potassium ion extraction rate is 86.46%. This integrated flotation‑conversion strategy provides a sustainable, efficient, and environmentally friendly pathway for comprehensive utilization of salt lake resources.