Mechanism Study on the Efficient Separation of Quartz and Petalite by Diamine Collector Under Neutral Conditions

To address the separation challenge of quartz and petalite due to their similar physicochemical properties, a neutral, fluoride-free flotation system was developed using the diamine collector N-dodecyl-1,3-propanediamine (ND13). Flotation tests on single minerals and mixed ores showed that efficient separation (selectivity index SI = 14.86) was achieved at pH = 7 with an ND13 concentration of 3.0 × 10-5 mol/L. Flotation kinetics revealed that both minerals followed the first-order classical model, with quartz achieving a maximum recovery of 97.6% and petalite 16.9%, corresponding to an optimal separation time of 58.7 s. Total organic carbon (TOC) analysis confirmed that the saturated adsorption capacity of ND13 on quartz (3.3 × 10-7 mol/g) was significantly higher than that on petalite within the studied concentration range. Adsorption isotherm modeling indicated that chemisorption dominated on quartz (Langmuir model R2 = 0.994), whereas multiple adsorption modes coexisted on petalite (Freundlich index n = 0.88). Zeta potential measurements indicated negligible electrostatic interaction on quartz (Δ = 0.20 mV), whereas petalite exhibited a more pronounced shift (Δ = 2.03 mV), suggesting stronger electrostatic adsorption. Interestingly, this enhanced electrostatic interaction did not translate into improved floatability. Complementary FTIR and XPS analyses revealed that ND13 adsorbed onto quartz predominantly through hydrogen bonding, while on petalite, both hydrogen bonding and electrostatic adsorption contributed comparably, resulting in reduced adsorption stability. This neutral separation system avoids the toxicity risks of traditional hydrofluoric acid processes and corrosion issues of acidic media, providing a novel green separation strategy for lithium mineral.