Summary：Metal ore beneficiation is a critical step in the mining industry, aimed at separating valuable metal minerals from gangue based on their physical or chemical property differences.

Metal ore beneficiation is a critical step in the mining industry, aimed at separating valuable metal minerals from gangue based on their physical or chemical property differences. The mainstream beneficiation methods can be broadly categorized into three groups: physical beneficiation, chemical beneficiation, and bio-beneficiation. Among these, physical beneficiation is the most widely applied due to its low cost and environmental friendliness. The selection of an appropriate beneficiation process depends largely on the characteristics of the target metal minerals, such as magnetism, density, and surface hydrophobicity.

Metal Ore Beneficiation Methods

1. Physical Beneficiation: The Low-Cost Solution for Broad Industrial Application

Physical beneficiation separates minerals without altering their chemical composition, relying solely on differences in physical properties. This approach is suitable for most easily liberated metal minerals. The four core physical beneficiation methods are:

1.1 Magnetic Separation: Targeted Recovery of Magnetic Metals

  • Core Principle: Utilizes differences in mineral magnetism (e.g., magnetite is attracted to a magnetic field, while gangue minerals are not) to separate magnetic from non-magnetic minerals.
  • Applicable Metals: Primarily iron, manganese, and chromium minerals. Particularly effective for magnetite (strong magnetic) and pyrrhotite (weak magnetic). Also used to remove iron impurities from non-metallic minerals like quartz sand.
  • Key Applications:
    • Iron ore beneficiation plants use a magnetic separation flow of roughing, cleaning, and scavenging to upgrade iron content from 25%-30% to over 65%.
    • Weakly magnetic minerals like hematite are first roasted to convert them into magnetite before magnetic separation.
  • Advantages: Low pollution, low energy consumption, and large processing capacity (single magnetic separators can handle thousands of tons per day).
Magnetic Separation

1.2 Flotation: “Hydrophobic-Hydrophilic” Separation of Fine Valuable Minerals

  • Core Principle: Chemicals (collectors and frothers) are added to make the target metal mineral hydrophobic. These particles attach to air bubbles and rise to the surface as froth, while non-target minerals remain in the pulp.
  • Applicable Metals: Copper, lead, zinc, molybdenum, gold, silver, and other fine-grained (typically <0.1mm) metals. Ideal for separating complex polymetallic ores (e.g., step-wise flotation of copper-lead-zinc ores).
  • Key Applications:
    • The standard process for copper ore: Sulfide copper flotation upgrades ore from 0.3%-0.5% Cu to a 20%-25% copper concentrate.
    • Auxiliary gold recovery: For finely disseminated gold, flotation first concentrates it into a sulfide concentrate, reducing cyanide consumption in subsequent cyanidation.
  • Advantages: High separation efficiency (recovery rates above 90%), effective for complex polymetallic ores.
  • Disadvantages: Use of chemical reagents requires wastewater treatment.
Flotation Machine

1.3 Gravity Separation: Exploiting Density Differences to Recover Coarse Heavy Metals

  • Core Principle: Gravity separation utilizes density differences between heavy metal minerals and lighter gangue in a gravitational or centrifugal field.
  • Applicable Metals: Gold (placer and lode coarse particles), tungsten, tin, antimony, especially coarse particles larger than 0.074 mm.
  • Key Applications:
    • Placer gold mining uses sluices and shaking tables to recover natural gold with over 95% recovery.
    • Tungsten and tin ores undergo gravity separation as a roughing step to discard 70%-80% of low-density gangue before flotation.
  • Advantages: No chemical pollution, very low cost, simple equipment.
  • Disadvantages: Low recovery for fine particles and minerals with small density differences.
Gravity Separation

1.4 Electrostatic Separation: Utilizing Conductivity Differences for Special Metals

  • Core Principle: Separates minerals based on differences in electrical conductivity (e.g., metallic minerals conduct, non-metallics do not) in a high-voltage field, where conductive minerals are attracted to or repelled by electrodes.
  • Applicable Metals: Mainly used for separating rare metal minerals like titanium, zirconium, tantalum, and niobium, or for cleaning concentrates (e.g., removing non-conductive gangue from copper/lead/zinc concentrates).
  • Key Applications:
    • Titanium separation from beach sands: In Hainan, electrostatic separation isolates conductive ilmenite from non-conductive quartz.
    • Concentrate purification: Removing poorly conductive quartz from tungsten concentrate to upgrade its grade.
  • Advantages: High separation precision, no chemical reagents.
  • Disadvantages: Sensitive to moisture (requires drying), low throughput, typically used only as a cleaning step.

2. Chemical Beneficiation: The “Last Resort” for Difficult Ores

When metal minerals are finely disseminated or tightly bound with gangue (e.g., oxidized ores, complex sulfides), physical methods may fail. Chemical beneficiation breaks down mineral structures to extract metals, mainly via:

2.1 Leaching: “Dissolution and Extraction” of Metal Ions

  • Core Principle: Ores are soaked in chemical solvents (acid, alkali, or salt solutions) to dissolve the target metal into a pregnant leach solution (PLS), from which the metal is recovered (e.g., by precipitation, cementation, or electrowinning).
  • Applicable Metals: Gold (cyanidation), silver, copper (heap leaching), nickel, cobalt, and other refractory metals.
  • Case Study:
    • Gold Cyanidation: Finely ground ore is mixed with a cyanide solution; gold forms a soluble complex and is later precipitated with zinc powder (recovery ≥90%). Cyanide pollution must be strictly controlled.
    • Copper Heap Leaching: Low-grade oxide copper ore (0.2%-0.5% Cu) is irrigated with sulfuric acid; copper dissolves and is recovered via solvent extraction and electrowinning (SX-EW) as cathode copper (cost-effective for low-grade ore).

2.2 Roasting-Leaching Combined Process

  • Core Principle: Ore is first roasted at high temperatures (300-1000°C) to alter its structure (e.g., oxidizing or reducing roast), converting refractory metals into a soluble form for subsequent leaching.
  • Applicable Metals: Refractory sulfides (e.g., nickel sulfide, copper sulfide) and oxide ores (e.g., hematite).
  • Case Study:
    • Nickel Sulfide Roasting: Converts nickel sulfide to nickel oxide, which is easily leached with sulfuric acid, avoiding sulfide interference.
    • Refractory Gold Ore Roasting: For ores containing arsenic and carbon, roasting removes arsenic (volatilized as As₂O₃) and carbon (which can adsorb gold), enabling subsequent cyanidation.

2.3 Microbial Beneficiation: An Environmentally Friendly Approach for Low-Grade Ores

  • Principle: Certain microorganisms (e.g., Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans) metabolically oxidize metal sulfides into soluble metal salts, enabling metal recovery from solution—also known as bioleaching.
  • Applicable Metals: Low-grade copper (e.g., porphyry copper), uranium, nickel, gold (as sulfur removal aid).
  • Advantages: Environmentally friendly (no chemical reagent pollution), low cost (microbes self-replicate), suitable for ores with copper grades as low as 0.1%-0.3%.
  • Disadvantages: Slow reaction rates (weeks to months), sensitive to temperature and environmental conditions.
  • Typical Application: Approximately 20% of global copper production comes from bioleaching, such as large heap leach operations in Chile.

3. The 3-Step Core Logic for Selecting Beneficiation Methods

3.1 Analyze Mineral Properties:

  • Magnetic minerals (e.g., magnetite) → Magnetic separation
  • Fine particles with hydrophobicity differences (e.g., copper ores) → Flotation
  • Coarse particles with high density (e.g., placer gold, tungsten) → Gravity separation

3.2 Evaluate Ore Grade and Liberation:

  • High-grade coarse ores → Gravity or magnetic separation (low cost)
  • Low-grade fine ores → Flotation or leaching (high recovery)
  • Extremely refractory ores → Chemical or bio-beneficiation

3.3 Balance Economics and Environmental Cost:

  • Prefer physical beneficiation for low energy use and minimal pollution
  • Resort to chemical or bio-methods only when physical methods are ineffective, weighing cost and environmental impact