Which Minerals Can Be Floated?

Extracting valuable minerals from ore is tricky. Many minerals won’t separate easily. But flotation gives us a powerful way to recover even tricky minerals. Here’s the full list of minerals that respond well to flotation.

Flotation works on many mineral types. The main groups are: non-ferrous metal sulfides ores, non-ferrous metal oxides ores, oxide/silicate/aluminosilicate minerals, polar minerals, alkali metal and its soluble salt minerals, and non-polar minerals. Each group requires different flotation methods and reagents. Proper separation depends on understanding each mineral’s surface chemistry. 

The surface physical and chemical properties of different minerals directly affect their floatability, so it is very important to master the types and characteristics of floatable minerals. Now let’s examine each mineral category in detail. Knowing these will help you choose the right flotation approach.

 

1. Non-Ferrous Metal Sulfide Ores

Sulfide ores are the easiest minerals to float. But not all respond equally. Some need special treatment for good recovery.

Most non-ferrous metal sulfide minerals float well with xanthate collectors. This includes copper sulfides (chalcopyrite, bornite), lead sulfides (galena), zinc sulfides (sphalerite), nickel sulfides (pentlandite), and iron sulfides (pyrite). Their natural hydrophobicity makes them ideal for flotation separation from gangue minerals.

 

Understanding Sulfide Mineral Flotation Behavior

Sulfide minerals share key characteristics that affect their floatability

Mineral	Formula	Natural Floatability	Common Collector
Chalcopyrite	CuFeS₂	Moderate	Xanthates
Galena	PBS	High	Xanthates
Sphalerite	ZnS	Low (needs activation)	Xanthates after CuSO₄ activation
Pyrite	FeS₂	Variable	Typically depressed

 

Key factors affecting sulfide mineral flotation

1. Surface oxidation – Fresh surfaces float better
2. Pulp potential – Affects collector adsorption
3. Activators/depressants – Modify mineral surfaces For example, sphalerite won’t float without copper sulfate activation. Pyrite often requires depressants to prevent unwanted flotation. The right pH control is critical – typically alkaline (pH 8-11) for sulfide flotation.

 

2. Non-Ferrous Metal Oxide Ores

Oxide minerals are trickier than sulfides. Many don’t respond to standard flotation methods. But the right approach can recover them.

Major oxide minerals that can be floated include malachite (copper), cerussite (lead), smithsonite (zinc), and hematite (iron). These typically need special collectors like fatty acids or hydroxamates rather than xanthates. Some require sulfidation first to make the surface behave like sulfides. 

Techniques for Oxide Mineral Flotation

Oxide minerals present unique challenges Direct flotation Uses collectors that bond with oxide surfaces Example: Fatty acids for iron oxides Works best for simple oxide systems Sulfidization flotation Converts oxide surfaces to sulfide-like Uses Na₂S + xanthate collectors Common for copper/carbonates Activation methods Metal ions can activate some oxides Example: Pb²⁺ for quartz flotation

Common oxide mineral treatment flows:

Mineral	Best Method	Collector	Special Requirements
Malachite	Sulfidization	Xanthate after Na₂S	pH control critical
Hematite	Direct	Fatty acid	Starch as depressant
Cassiterite	Direct	Arsenic acid	Needs fine grinding

 

 

3. Oxide, Silicate & Aluminosilicate Minerals

Quartz, feldspar, and mica – these common gangue minerals can sometimes become valuable targets. Selective flotation makes separation possible.

Many oxide/silicate minerals can be floated using ionic collectors. Examples include quartz (floats with amines), feldspar (amines with HF activation), and kaolinite (fatty acids). These minerals often require careful pH control and specific depressants to achieve separation from valuable minerals.  

Processing Strategies for Silicate Minerals

Silicate flotation depends heavily on surface charge:

1. Cationic flotation(amine collectors)

• Works for SiO₂ (quartz) at pH 2-4
• Minerals are negatively charged
• Collector: Primary amines

2. Anionic flotation(fatty acids)

For minerals with a positive charge

Example: Feldspar with HF treatment Important factors:

• Particle size: Silicates often need ultra-fine grinding
• Slimes: Can coat surfaces and prevent flotation
• Water quality: Dissolved ions affect performance

 

Common aluminosilicate separations:

Separation	Method	Conditions
Quartz/feldspar	Cationic at pH 2	HF as activator
Mica/quartz	Anionic at pH 8	Fatty acid collector
Kaolin refining	Selective flocculation	Complex process

 

 

4. Polar Minerals

Some minerals have strong charge separation at their surfaces. These polar minerals need special handling to float properly.

Polar minerals like calcite, fluorite, and apatite require fatty acid collectors or hydroxamates for flotation. Their floatability depends heavily on pH control and the use of specific depressants. For example, calcite floats best at pH 8-10 with oleate, while depressing silica with sodium silicate.

 

Key Factors for Polar Mineral Flotation

Surface charge characteristics:

• Zero charge points vary by mineral
• Example: Calcite pHpzc ~9.5
• Affects collector adsorption efficiency

 

Typical collectors used:

Mineral	Collector Type	pH Range
Fluorite (CaF₂)	Oleic acid	8-10
Apatite	Fatty acids	9-11
Barite	Alkyl sulfates	6-8

 

Common challenges:

• Similar surface properties make separation difficult
• Example: Separating calcite from apatite
• Requires selective depressants like phosphates/starch

 

Process variations:

• Reverse flotation is often used
• Sometimes needs heating (30-60°C)
• Ion composition in water affects the results

 

5. Alkali Metal Salts

You might not expect it, but even soluble salts can be separated by flotation under the right conditions.

Important soluble salt minerals include sylvite (KCl), halite (NaCl), and carnallite (KMgCl₃·6H₂O). These are floated using amine collectors in saturated brine solutions. The key is maintaining saturation to prevent mineral dissolution, with specific depressants separating NaCl from KCl.

Salt Mineral Flotation Technology

Special process requirements:

• Must maintain saturated brine solution (~315g/L)
• Temperature control is often needed
• Clay content significantly affects the results

 

Chemical regime:

Component	Function	Typical Usage
Amine collector	Makes KCl hydrophobic	100-300g/ton
Depressant (e.g. guar gum)	Prevents NaCl flotation	50-200g/ton
Frother (MIBC)	Stabilizes bubbles	20-50g/ton

 

Processing variations:

• Two main approaches: Direct flotation of KCl and reverse flotation of NaCl
• Particle size critical (0.1-2mm ideal)
• Often needs de-sliming first

 

Industrial applications:

• Potash processing (~90% KCl)
• Lithium brine processing
• Salt purification

 

6. Non-Polar Minerals

Some valuable minerals are naturally hydrophobic – they repel water and float easily. But getting good separation still requires proper technique.
Key non-polar minerals include graphite, sulfur, talc, molybdenite, and coal. These often float without collectors, just using frothers. However, specific depressants help separate them from similar minerals. For example, dextrin is used to depress carbonaceous material when floating sulfide ores.

Processing Non-Polar Minerals

Natural float ability explained

1. Crystal structure determines hydrophobicity

2. Example: Graphite’s layered structure traps air

3.Contact angles >90° indicate good floatability

 

Common processing methods

Mineral	Typical Process	Specialty Reagents
Graphite	Multiple cleaning stages	Kerosene sometimes added
Molybdenite	Cu-Mo separation	Nokes reagent to depress
Coal	Frother only (MIBC)	Diesel for poor-quality coal

 

Key challenges

1. Fine particle recovery difficult

2. Slime coating problems common

3. Oxidized surfaces reduce float ability

 

Special cases

1. Sulfur flotation at 65-75°C

2. Talc depression in base metal flotation

3. Bitumen recovery from oil sands

 

Conclusion

Flotation works for many mineral types beyond just sulfides. Key categories include sulfide ores (easiest), oxide minerals (needing special collectors), silicates (charge-dependent separation), polar minerals like salts, and even non-polar minerals like graphite. Each mineral group requires specific collectors, pH conditions, and often activators or depressants. Understanding these differences is crucial for designing effective mineral processing flowsheets.