In the non-ferrous metal beneficiation industry, sodium sulfide is a highly cost-effective and versatile inorganic regulator suitable for the flotation of copper, lead, zinc, molybdenum, and other primary sulfide ores, as well as secondary oxidized and共生 composite ores. Due to its unique hydrolysis properties in water, sodium sulfide can activate, inhibit, remove reagents, and regulate pulp conditions. It solves the problem of low recovery of low-grade oxidized ores and achieves precise separation of multi-metal concentrates, making it an essential reagent for improving efficiency and reducing costs in beneficiation plants.
I. Basic Physicochemical Properties and Flotation Adaptation Mechanism of Sodium Sulfide
1.1 Basic Physicochemical Adaptation Properties
Industrial-grade sodium sulfide is typically available in flake or granular solid form. It is readily soluble in alkaline pulp, with strong stability in aqueous solution. It acts quickly at room temperature without additional heating, making it suitable for room-temperature flotation lines. Sodium sulfide is inherently alkaline and can raise the pulp pH without auxiliary agents, meeting the basic requirements of high-alkali non-ferrous metal flotation. It is easy to store and transport, requiring only simple airtight storage, and is suitable for small and medium-scale beneficiation plants. Its comprehensive cost, including procurement and operation, is much lower than that of complex organic regulators.
1.2 Pulp Hydrolysis Core Reaction and Active Components
When dissolved in pulp, sodium sulfide undergoes stepwise reversible hydrolysis, generating active components without interfering by-products. The stepwise hydrolysis is stable and controllable, producing hydrosulfide ions (HS⁻), hydroxide ions (OH⁻), and a small amount of hydrogen sulfide gas. The long-lasting active components in the pulp are HS⁻ and S²⁻, which, combined with the alkaline environment, adapt to various non-ferrous metal flotation conditions. These active species act specifically on mineral surfaces without waste or adverse effects such as slime contamination or sticky froth.
1.3 Core Flotation Mechanisms
Three core mechanisms are involved: (1) Interface modification and sulfurization film formation: For hydrophilic oxidized minerals, active sulfur ions react with surface metal cations to form a dense hydrophobic sulfide film, enabling subsequent adsorption of xanthate collectors. (2) Competitive adsorption inhibition: At high concentrations, active sulfur species preferentially occupy active sites on sulfide mineral surfaces, displacing adsorbed collectors and preventing re-adsorption, thereby enhancing mineral hydrophilicity and achieving precise inhibition. (3) Potential regulation: Sodium sulfide simultaneously optimizes pulp pH and redox potential, ensuring optimal flotation conditions for different minerals and avoiding issues like tailings loss and concentrate downgrading.
II. Applications of Sodium Sulfide in Non-Ferrous Metal Flotation
2.1 Efficient Sulfidizing Activator for Oxidized Non-Ferrous Ores
This is the largest and most common application of sodium sulfide in mining. Oxidized ores such as malachite, azurite, cerussite, and smithsonite are naturally hydrophilic, making direct flotation with conventional collectors ineffective. Adding sodium sulfide triggers in-situ sulfurization, forming a micron-thick hydrophobic sulfide film on the ore surface, replicating the flotability of primary sulfide ores. Standard collectors and frothers can then be used. Plant data show that for high-oxidation copper-lead-zinc ores, without sodium sulfide, recovery is below 20%; with standardized sodium sulfide addition, recovery stabilizes at 65–80%. This significantly improves efficiency and is suitable for upgrading old oxidized ore flotation lines.
2.2 Selective Inhibitor for Precise Separation of Multi-Metal Sulfide Ores
In preferential flotation of complex共生 sulfide ores such as Cu-Mo, Cu-Pb, Pb-Zn, and Cu-Zn, and in cleaning of bulk concentrates, sodium sulfide is a low-cost, highly selective inorganic inhibitor. It achieves the goal of “inhibiting more, floating less; inhibiting impurities, retaining the main metal.” The inhibition strength follows a clear gradient based on surface lattice properties and adsorption energy: galena is most strongly inhibited, followed by sphalerite, chalcopyrite, bornite, and pyrite. Molybdenite, with its natural floatability and inert surface, is largely unaffected by standard sodium sulfide dosages. A key application is in Cu-Mo bulk concentrate separation. Adding high-purity sodium sulfide desorbs xanthate collectors from copper minerals, depressing them and allowing molybdenite to float and concentrate, producing high-grade molybdenum concentrate while copper is recovered from the tailings. This balances separation accuracy and metal recovery, replacing expensive organic inhibitors and reducing reagent costs.
2.3 Depressant for Bulk Flotation Concentrates
After bulk flotation, residual collectors, frothers, and flocculants on the concentrate surface can interfere with subsequent separation, causing mutual contamination, low grade, and metal loss. Sodium sulfide has strong ion-exchange desorption ability, effectively removing residual organic reagents from sulfide and oxidized mineral surfaces without secondary contamination. The standard practice is to dewater and densify the bulk concentrate, add sodium sulfide with strong agitation, wash to remove desorbed reagents, and then proceed to separation. This simple, adaptable process achieves nearly 100% removal efficiency and suits large-scale continuous operations.
2.4 Pulp pH and Potential Stabilizer Throughout Flotation
Stable pulp conditions are critical for consistent flotation performance. Sodium sulfide acts as both an alkali and a potential regulator. It raises and stabilizes pulp pH in the optimal alkaline range of 9.0–12.0, preventing acidic corrosion and loss of reagent activity, and adapts to all non-ferrous mineral flotation. It also lowers the pulp redox potential, creating a stable electrochemical environment, reducing interference from oxidizing ions, and avoiding slime agglomeration and reagent failure. Compared to single-function regulators like lime or soda ash, sodium sulfide simultaneously regulates conditions and aids separation, simplifying reagent addition and plant operation.
Post time: May-18-2026
