Flotation method of lead-zinc oxide ore
Oxygenated lead-zinc ore has a high oxide content and is relatively fragile, easily breaking during mining. Furthermore, this mineral composition is complex and difficult to separate. Currently, common flotation methods for oxidized lead-zinc ore include sodium oxide sulfide flotation, sulfur sulfide flotation, flocculation flotation, and combined reflotation and separation.
1. Flotation Methods for Oxygenated Lead-Zinc Ore - Sodium Oxide Sulfide Flotation:
Oxygenated lead-zinc ore has low floatability, making it difficult to extract high-quality ore using conventional collectors. Sulfide-xanthate flotation and sulfide-amine flotation are commonly used. Sulfide-xanthate flotation involves sulfiding zinc oxide with sodium sulfide, adding copper sulfate as an activator, and flotating with a high-grade xanthate collector. Sulfide-xanthate flotation is suitable for treating lead oxide minerals. Sulfide-amine flotation involves sulfiding zinc oxide with sodium sulfide, then flotating it with a fatty amine collector. The sulfide-amine flotation method for oxidized lead-zinc ore is suitable for treating oxidized zinc ore containing easily muddy gangue, but its process is complicated, requires desludging equipment, and can only be achieved under the conditions of large amounts of sulfuric acid cleaning and activation.
2. Flotation Method for Oxidized Lead-Zinc Ores - Sulfur Sulfide Flotation:
Sulfur sulfide flotation uses sulfur powder to sulfide the oxidized lead-zinc ore. This treatment forms a sulfide film on the surface of the ore, enabling separation of the oxidized lead-zinc ore. However, this process requires high temperature and high pressure conditions and is currently rarely used.
3. Flotation Method for Oxidized Lead-Zinc Ores - Flocculation Flotation:
Flocculation flotation of oxidized lead-zinc ore involves vigorously agitating the fine-grained minerals by adding a high-molecular-weight compound to impart hydrophobicity, followed by the addition of a collector for flotation. Flocculation flotation is suitable for separating fine-grained oxidized lead-zinc ores. However, due to the difficulty and high cost of developing high-molecular-weight flocculants, it is not currently used in practice.
4. Flotation Method for Oxidized Lead-Zinc Ores - Combined Gravity and Flotation:
Due to the unique properties of some oxidized lead-zinc ores, a combined gravity and flotation process is sometimes used to recover the valuable minerals. The minerals with higher density or magnetic properties are recovered by gravity separation or magnetic separation, or the tailings are discarded by gravity separation. Gravity and flotation separation is suitable for ores with a large difference in density between metal minerals and gangue minerals or with magnetic properties.
The main uses of flotation methods for lead-zinc oxide ores are:
1. After flotation of the sulfide minerals, a sulfiding agent is added to sulfide the oxide minerals, and then the flotation process is carried out according to the flotation method for lead and zinc sulfide ores.
2. When the gangue is primarily silicate, a gangue depressant is added, and fatty acids are used to capture the lead and zinc minerals.
3. Sodium sulfide is used as an activator for zinc oxide ores, and fatty amines are used to float zinc oxide minerals in an alkaline medium.
For mixed ores, the flotation process for lead-zinc oxide ores can be based on either the "lead first, then zinc" or "sulfur first, then oxygen" principle. Specifically, the flotation sequence is as follows:
1. Galena - lead oxide minerals - sphalerite - zinc oxide minerals;
2. Galena - sphalerite - lead oxide minerals - zinc oxide minerals.
When cerussite has good floatability and sphalerite has poor floatability, the first process can yield better results. Otherwise, the second process should be used. The second process prevents interference from HS- and S- remaining in the pulp after cerussite sulfidation on sphalerite flotation, facilitating sphalerite flotation and reducing the amount of zinc flotation collector required. This may also reduce the zinc content in the lead concentrate.
Flotation methods for oxidized lead-zinc ores are primarily applicable to cerussite (PbCO3), lead alum (PbSO4), arsenopyrite (Pb5(AsO4)3Cl), crocoite (PbCO4), pyromorphite (Pb5(PO4)3Cl), and wolfenite (PbMoO4). Cerussite, lead alum, and wolfenite are easily sulfided using sodium sulfide, calcium sulfide, or sodium hydrosulfide. However, sulfidation of lead alum requires a longer contact time and a relatively large amount of sulfiding agent. Arsenite, chromite, pyrochloreite, etc. are difficult to sulfide and have poor floatability. Most of them will be lost in the tailings during flotation.
Sodium sulfide is commonly used as a sulfiding agent for flotation of lead oxide minerals. However, process conditions must be carefully considered during sulfidation. Excessive sodium sulfide should be avoided, as it can lead to excessive concentrations of hydrogen sulfide (HS-) and sulfur (S2-) ions in the slurry, inhibiting the flotation of the sulfided lead oxide minerals. Excessive sodium sulfide can also cause the slurry pH to exceed ±0.5, which is also detrimental to flotation. To avoid the harmful effects of excessive sodium sulfide, sodium sulfide can be added in stages or a small amount of copper sulfate or ferrous sulfate can be added after sulfidation to precipitate the harmful ions. Slow, non-aerated agitation is recommended during sulfidation to minimize oxidation of the sodium sulfide and prevent the sludge film from flaking off the ore particles. The pH during flotation should be maintained between 8.5 and 10. A small amount of ammonium sulfate should be added to prevent calcium and magnesium hydroxides from forming harmful Ca(OH)2 and Mg(OH)2 films on the cerussite surface.
After lead oxide minerals are sulfided, the most effective collector is a long-chain xanthate. For example, sec-octyl xanthate is more effective than butyl and pentyl xanthates, and No. 25 black powder is also effective. While fatty acid collectors such as oleic acid and oxidized paraffin soap can directly capture lead oxide minerals, their poor selectivity makes them unsuitable for ores primarily composed of carbonates or high in iron oxide. They can only be used for high-grade ores with silicate as the primary gangue.
For mixed ore, the flotation process for lead-zinc oxide ores is generally best to first float out the lead sulfide, then add a sulfiding agent and xanthate to flotate the lead oxide. If fine mud and soluble salts are a significant concern, desliming or the addition of dispersants such as water glass can be used to mitigate their effects.
The above are common flotation methods for lead-zinc oxide ores. Depending on the ore's properties and degree of oxidation, the flotation process used varies. Therefore, it is recommended that miners conduct mineral processing tests and, based on the test reports, customize a scientific and appropriate flotation process to improve flotation performance and minimize economic losses.
Flotation Methods for Lead-Zinc Oxide Ores: During the flotation process, sulfide is first added to sulfidize the mineral for subsequent flotation. The following considerations should be taken into account when sulfiding lead oxide ores: First, cerussite, pyroclastics, and wulfenite are more susceptible to sulfidation. Sulfiding agents such as sodium sulfide, calcium sulfide, and sodium hydrosulfide can be used for treatment. However, pyroclastics require a longer contact time and a relatively large amount of sulfiding agent. However, arsenite, chromite, and pyromorphite are difficult to sulfidize and have poor floatability, with a large portion being lost in the tailings during flotation. Secondly, the dosage of sulfiding agent must be carefully considered during the addition process. Excessive sulfiding agent will inhibit the flotation of lead oxide minerals and cause the pH to be too low, which is detrimental to the flotation process. The effects of excessive sulfiding agent can be reduced by adding sodium sulfide in stages, or by adding small amounts of copper sulfate or ferrous sulfate. Furthermore, during the flotation stage, long-chain xanthate is a common and effective collector. Depending on experimental results, sec-octyl xanthate or No. 25 black medicine can also be selected. Fatty acid collectors, such as oleic acid and oxidized paraffin soap, have poor selectivity and are only suitable for high-grade lead ores with silicate as the primary gangue.
Case Study 1: Application of Flotation Methods for Oxide Lead-Zinc Ore
A lead-zinc oxide ore is a mesothermal hydrothermal replacement deposit. Ore types include sulfide, oxide, and mixed ores. Primary metallic minerals are primarily galena and sphalerite, along with pyrite, limonite, and hematite. Metallic oxide minerals primarily include cerussite, vanadium, smithsonite, zincite, and hydrozincite, with minor amounts of willemite, hemimorphite, and ferrovanadium. Of the zinc oxide minerals, smithsonite and zinc oxide account for approximately 80%, willemite and hemimorphite for 18%, and zinc sulfate for approximately 2%. Gangue minerals primarily consist of calcite, dolomite, barite, quartz, and clay. The ore has a dense structure with uneven distribution of coarse and fine particles. The particle size of galena and sphalerite generally ranges from 0.01 to 12 mm. The content of lead and zinc in the original ore is: lead grade 1%~2%, oxidation rate 20%~30%; zinc grade 6%~7%, oxidation rate 20%~40%, sometimes reaching 50%.
Flotation Application Case Study 2 for Oxidized Lead-Zinc Ore:
In a lead-zinc ore processing plant design project in Tibet, the oxidized ore contained approximately 5% lead and 15% zinc. It also contained 80.4g/t silver and 0.2g/t gold, resulting in oxidation rates of 12.81% for lead and 15.15% for zinc, respectively. Taking into account the local geographical and climatic characteristics and ore properties, our company, after testing, adopted a preferential flotation process for the oxidized lead-zinc ore. A comprehensive reagent system and tailings treatment system were configured for the ore, resulting in optimal recovery of both lead and zinc concentrates and maximum silver concentration in the lead concentrate.
