Effect of the Combined Depressant of Sodium Humate and Calcium Chloride on the Flotation Behavior of Cu²⁺-Activated Sphalerite and Pyrite

During the flotation of lead-zinc sulfide ores, the activation of sphalerite by CuSO4 enhanced the floatability of both sphalerite and pyrite, making their effective separation challenging. To achieve the selective separation of these two minerals, this study investigated the impact of a combined depressants comprising sodium humate (NaHA) and calcium chloride (CaCl₂) on the flotation behavior of sphalerite and pyrite under Cu²⁺ activation, along with their selective depression mechanism. Micro-flotation tests demonstrated that the combination of NaHA and CaCl₂ selectively depressed pyrite while exerting a minimal effect on the floatability of sphalerite. At pH 9, with copper sulfate dosage of 2.5 mg·L-1, sodium humate dosage of 20 mg·L-1 and calcium chloride dosage of 50 mg·L-1, the recovery of sphalerite reaches 95.17%, while the recovery of pyrite is only 48.86%. The mixed mineral flotation tests also demonstrated that the floatability of pyrite was more significantly depressed by NaHA+CaCl2 than sphalerite, with the recovery of Zn ad Fe being 58.16% and 26.63%, respectively. Mechanistic studies showed that single NaHA exerted weak depression on both minerals after Cu²⁺ activation. The synergistic effect of NaHA and CaCl₂ promoted NaHA adsorption on pyrite. Ca²⁺ reacted with the carboxyl groups of NaHA to strengthen its adsorption on pyrite, and free Ca²⁺ may further complex with humate ions to form precipitates, which might potentially deposit on or associate with the mineral surface. By comparison, the hydrophobic CuS layer on activated sphalerite hindered the adsorption of Ca²⁺ and humate ions, maintaining its good floatability. This study verified that the combined depressant NaHA+CaCl₂ realized efficient separation of sphalerite from pyrite under low-alkalinity conditions, which offers theoretical and technical support for the eco-friendly separation of zinc-sulfur mixed concentrates.