Flotation separation of chalcopyrite from pyrite using lime or cyanides as depressants results in serious problems, such as the blockage of pipelines and environmental pollution. Eco-friendly organics are a future trend for beneficiation plants. In this research, the eco-friendly organic depressant sodium humate (SH) was chosen as a depressant to separate chalcopyrite from pyrite by flotation. The results indicated that SH could selectively depress pyrite owing to the oxidation species (FeOOH, Fe₂(SO₄)₃) on its surface. The oxidation species were the adsorption sites for the COO^- in the SH structure and impeded the subsequent collector potassium ethyl xanthate (KEX) adsorption. However, chalcopyrite was slightly oxidized with fewer oxidation species for SH adsorption, and KEX could be adsorbed and functioned effectively. This research suggested that SH could be an effective and eco-friendly depressant in chalcopyrite-pyrite flotation separation, which had potential use in the industry.

Current flotation practices using lime or cyanide as depressants in chalcopyrite and pyrite separation have significant disadvantages, such as substantial reagent consumption, high slurry pH, and environmental hazards. This work aimed to explore the utilization and mechanisms of tannic acid (TA) as an eco-friendly alternative to lime or cyanide in chalcopyrite-pyrite separation. Flotation results showed that TA selectively depressed pyrite yet allowed chalcopyrite to float at neutral or alkaline pH. Adsorption density and zeta potential results indicated that TA adsorbed intensely on pyrite but minorly on chalcopyrite. Besides, potassium ethyl xanthate was still largely adsorbed on chalcopyrite but not on pyrite after TA adsorption. Surface analysis by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy further showed that the oxidation species of FeOOH and Fe₂ (SO₄)₃, particularly FeOOH were the main active sites for TA chemical adsorption. Owing to the greater and faster oxidation of pyrite, more FeOOH and Fe₂ (SO₄)₃ were generated on the pyrite surface, and the chemical adsorption of TA was more pronounced on the pyrite surface than on the chalcopyrite surface.

In order to separate fluorite and calcite inhibited in tungsten tailings, the effect and mechanism of using ultrasonic external field activation to separate fluorite and calcite inhibited by sodium hexametaphosphate in a sodium oleate system were investigated. After pretreatment with an ultrasonic external field with a frequency of 40 kHz and sound intensity of 0.56, 0.50 and 0.40 W/cm², the flotation recovery of calcite could be increased from 16.08% to about 80%, while the flotation recovery of fluorite was only increased from 7.5% to about 20%, with a difference of 60% between the two flotation recoveries, and the larger the sound intensity, the shorter the pretreatment time and the smaller the ultrasonic input energy. The contact angle of the calcite surface increased, sodium oleate adsorption increased, and zeta potential decreased after ultrasonic pretreatment, while the contact angle, sodium oleate adsorption, and zeta potential of fluorite surface were less changed. The results of heat of adsorption and XPS measurements showed that more heat was released from the interaction between sodium hexametaphosphate and fluorite, and the Ca2p peaks on the surface of fluorite were shifted to a greater extent after the interaction, which inferred that the adsorption of fluorite and sodium hexametaphosphate was relatively easier and stronger. It is presumed that the ultrasonic pretreatment can bring the mineral surface to different degrees of desorption according to the adsorption strength of sodium hexametaphosphate, exposing Ca²⁺ active sites for sodium oleate adsorption, while expanding the floatability difference between fluorite and calcite.