A Comprehensive Guide to the Properties of Galena and the Complete Flotation Separation Process

Galena is the key sulphide mineral in the industrial extraction of lead and is often found in association with sphalerite, pyrite and chalcopyrite to form lead-zinc polymetallic deposits. The crystals have a cubic structure within the isometric crystal system. Galena possesses inherent hydrophobic and semiconducting properties, and its crystal lattice is prone to contamination by impurity elements such as silver, zinc, copper, antimony and bismuth. Different impurities alter the mineral’s conductivity type, directly affecting the adsorption reaction between the mineral surface and flotation reagents, and thus determining the quality of its flotability. The surface of galena is highly susceptible to oxidation; factors such as the pH, dissolved oxygen and various unavoidable ions present in the grinding and flotation slurries can alter its surface hydrophilic or hydrophobic state, which is the core reason for the difficulty in separating lead from zinc.

The industry’s separation of galena centres on the flotation process. The overall workflow comprises five fixed stages: grinding and pre-treatment, slurry conditioning, selective roughing, multi-stage scavenging, and middlings recycling. A tailored reagent system is employed to achieve efficient separation of lead from zinc, sulphur and copper minerals.

The first step involves classification and grinding, during which grinding media interact with galena and associated sulphide minerals to produce electrochemical reactions via galvanic cells, altering the degree of oxidation on the mineral surfaces. To minimise adverse effects, high-chromium, stainless steel or ceramic grinding media are prioritised in production to reduce the leaching of iron ions; simultaneously controlling the oxidation atmosphere during grinding by introducing nitrogen to reduce the oxygen content in the slurry, thereby minimising the formation of hydrophilic oxidation products on the galena surface and ensuring the effectiveness of subsequent reagent adsorption. The grinding fineness is precisely adjusted according to the grain size distribution of the minerals to achieve complete individual liberation of galena from gangue and associated minerals.

The slurry from the grinding stage enters the slurry adjustment process, where the pH is adjusted and modifiers are added according to the ore’s associated components. If the ore contains a large amount of sphalerite, lime and sodium hydroxide are used to create an alkaline slurry environment, combined with zinc sulphate and new-generation organic inhibitors to suppress zinc minerals; for copper-bearing associated ores, specialised impurity removal reagents are added to eliminate the adverse effects of copper ions activating sphalerite and to reduce lead-zinc intergrowth issues. During the slurry conditioning stage, xanthate-type selective collectors are simultaneously introduced; through electrochemical reactions, the reagent molecules are stably adsorbed onto the surface of galena, enhancing its hydrophobic properties.

Once slurry preparation is complete, roughing flotation is carried out; the flotation foam constitutes the lead rough concentrate, whilst the tailings in the tank are sent to the scavenging stage to recover residual galena, with the scavenging foam returned as intermediate concentrate to the upstream grinding or slurry preparation stage via a closed-circuit system to prevent metal loss. The grade of the rough concentrate typically does not meet smelting standards and must therefore be sent for multi-stage concentration and purification. In the fine selection stage, inorganic or organic inhibitors are added in stages to continuously suppress the flotation of sphalerite and pyrite, thereby gradually stripping zinc and sulphur impurities from the concentrate.

The reagent combination can be flexibly adjusted to suit the characteristics of different ores: whilst inorganic inhibitors are highly effective, they present environmental drawbacks; green organic inhibitors such as humic acid salts and CMC are less toxic, and their combined use can achieve a synergistic effect in suppressing impurities. All flotation foam is combined to form qualified lead concentrate, whilst the flotation tailings and sweep tailings are consolidated and discharged, thereby completing the entire galena beneficiation process. The entire process relies on the regulation of pulp potential, pH and reagent ratios, utilising the unique electrochemical flotation characteristics of galena to balance lead recovery rates with concentrate purity; it is a universal and mature beneficiation solution for all types of lead-zinc co-occurring deposits.