The beneficiation of tungsten ore (the mineral processing of tungsten ores) is a complex process, as tungsten minerals (mainly wolframite and scheelite) exhibit different physicochemical properties and often coexist closely with associated minerals (such as tin, molybdenum, bismuth, sulfides, etc.).
The selection of a specific mineral processing technology primarily depends on the type of ore (wolframite or scheelite), dissemination size, associated mineral types, and ore grade.
Below is a detailed explanation of the mainstream tungsten ore beneficiation methods and processes currently used in industry:
1. Core principle: Pre-enrichment, early harvest and maximizing harvest
Tungsten ores typically have a low grade (0.2%-1% WO₃), and tungsten minerals are brittle, prone to over-grinding and subsequent loss during the grinding process. Therefore, the core principle of tungsten ore beneficiation is: "Collect as early as possible, and discard as early as possible."
Stage grinding and stage separation: Avoid grinding too finely at once, dissociate minerals in stages, and recover coarse tungsten concentrate.
Gravity separation priority: Leveraging the high specific gravity of tungsten minerals, recovery by gravity separation should be employed as much as possible after coarse grinding.
2. Main mineral processing methods
A. Gravity Separation - the most commonly used and economical method
This is the preferred method for processing tungsten ore, especially wolframite, due to its high specific gravity (around 7.5), which significantly differs from that of gangue minerals.
Applicable object: Wolframite ((Fe,Mn)WO₄), also used for the pre-concentration of scheelite.
Common equipment:
Jig machine: used for processing coarse-grained ores and recovering coarse-grained tungsten concentrate.
Jig Machine
Shaking Table: Used for processing medium to fine-grained ores, it boasts high separation accuracy and is a key equipment for tungsten ore beneficiation.
Shaking Table
Spiral chute: used for processing fine particles as an auxiliary means.
Spiral Concentrator
Centrifugal concentrator: for efficient recovery of fine-grained tungsten slime.
Process characteristics: raw ore crushing -> rod milling (to reduce over-crushing) -> jig machine (to collect coarse particles) -> ball milling -> table shaking (to collect fine particles).
B. Flotation method
When the ore is disseminated in extremely fine particles or the main mineral is scheelite, the efficiency of gravity separation decreases, necessitating the use of flotation.
Applicable objects:
Scheelite (CaWO₄): Scheelite has a relatively low specific gravity (around 6.0) and often coexists with calcium-containing minerals such as calcite and fluorite, making separation difficult. It is mainly separated by flotation.
Fine-grained wolframite: The micro-fine fraction that cannot be recovered by gravity separation.
Key difficulty: The surface properties of scheelite are similar to those of calcite and fluorite, making separation challenging.
Commonly used medications:
Collector: fatty acids (such as oleic acid, oxidized paraffin soap), phosphonic acids.
Inhibitors: water glass (commonly used), starch, tannic acid (used to inhibit gangue).
Adjusting agent: Lime (used to adjust pH value, typically for flotation of scheelite under alkaline conditions).
Special process: "Petrov Process", also known as heating flotation, utilizes the differences in the adsorption capacity of different minerals for collectors at high temperatures (80-90°C) to separate scheelite from calcite/fluorite.
C. Magnetic Separation
Tungsten ore itself is usually non-magnetic or weakly magnetic, and magnetic separation is mainly used for impurity removal or separation of associated minerals.
High-intensity magnetic separation: used to remove iron-containing gangue, or in some cases, to separate wolframite (weakly magnetic) from non-magnetic gangue (less common, requiring high-gradient magnetic separation).
Main purposes:
Remove the iron impurities from the ore.
If magnetite is present as an associated mineral, it should be removed through magnetic separation first to reduce subsequent workload.
Wolframite exhibits weak magnetism, and can sometimes be separated from non-magnetic gangue, particularly the fine slime fraction, using a high-gradient magnetic separator.
D. Electrostatic Separation
Sorting is carried out based on the differences in conductivity of minerals.
Purpose: Typically used as a fine selection operation for gravity concentrate.
Scenario: Separate the mixed concentrate obtained through gravity separation (containing wolframite, cassiterite, ilmenite, monazite, etc.). Wolframite is a conductor, while gangue such as quartz is a non-conductor, which can be further purified through electrostatic separation.
3. Typical processes for different types of ores
Scenario 1: Wolframite - quartz vein type (the most common)
This type of ore has a relatively coarse dissemination size and is easy to disintegrate.
Manual selection/photoelectric selection: Remove large waste rocks before crushing.
Crushing and grinding: Rod mills are used (to reduce sliming) and "stage grinding" is implemented.
Re-election:
Coarse fraction -> Jigging machine -> Obtain coarse concentrate.
Medium and fine particle size -> Shaker table -> Obtain fine concentrate.
Selected: The re-selected coarse concentrate often contains impurities such as tin, sulfur, and arsenic, which require processing through:
Flotation desulfurization and arsenic removal.
Magnetic separation for iron and manganese removal.
Electro-separation of cassiterite and ilmenite.
Finally, high-grade wolframite concentrate is obtained.
Scenario 2: Scheelite - Skarn Type (Relatively Difficult)
This type of ore often coexists with sulfides, calcite, and fluorite, with fine dissemination size.
Flotation desulfurization: First, use xanthate-based reagents to flotate and remove sulfides (such as chalcopyrite and pyrite).
Gravity separation pre-concentration (optional): If the particle size allows, first use a spiral chute to discard some of the tailings.
White tungsten flotation:
Use fatty acid collectors.
Use water glass to suppress gangue.
If there is a high content of calcite/fluorite, it may be necessary to conduct heated flotation or multiple cleanings.
Chemical treatment: For scheelite concentrate (high in calcium) that is extremely difficult to beneficiate, it is sometimes directly sent to hydrometallurgical plants for processing, without pursuing extremely high physical beneficiation grades.
Scenario 3: Mixed white and black tungsten ore
Joint process required:
First, re-select and recycle coarse-grained wolframite.
Re-grind the tailings after gravity separation.
Recover fine-grained wolframite and scheelite through flotation (sometimes separate flotation is required, and sometimes they are mixed and then separated after flotation).
4. Selection suggestions and precautions
If you are considering how to select a process for a specific tungsten mining project, it is recommended to follow the steps below:
Detailed mineralogical studies (crucial):
Conduct process mineralogy analysis: Determine the primary form in which tungsten exists (wolframite or scheelite)?
Determine the dissemination particle size: is it coarse, medium, or fine? This determines the grinding fineness and whether gravity separation is applicable.
Determine the associated minerals: Are there tin, molybdenum, bismuth, fluorite, and calcite? This determines whether a complex separation process is required.
Small-scale experiment and scaled-up experiment:
Do not directly apply the processes of other mines. Sampling must be conducted for laboratory mineral processing tests to determine the optimal reagent system, grinding fineness, and equipment combination.
Environmental considerations:
Tungsten ore beneficiation often involves heavy metals (such as arsenic and lead) and a large amount of chemicals (such as water glass and fatty acids). Tailings treatment and wastewater recycling are key focuses in the design of modern beneficiation plants.
Economic balance:
Gravity separation has low cost but its recovery rate is limited by particle size; flotation has a high recovery rate but incurs high costs and reagent consumption. Typically, a "gravity-flotation combined" process is adopted to achieve the best cost-performance ratio.
Summary:
Wolframite: The preferred method is gravity separation (jigging + table concentration), supplemented by magnetic separation and fine separation through electrostatic separation.
Scheelite: Flotation is the preferred method, with a focus on solving the separation issue with calcareous minerals.
Mixed ore/fine slime: Adopt a combined gravity-flotation process, and even introduce new technologies such as centrifuges and carrier flotation.
