In the flotation workshop, Xanthate is undoubtedly the most famous “collector-in-chief”—it is powerful and versatile. But if you ask an experienced shift supervisor, “If you want to recover more gold and silver, or separate lead and zinc, what should you use?”
Chances are, he will point to a dark-colored barrel in the corner and say mysteriously, “Try adding some black medicine.”
This type of reagent often appears pitch-black, has a pungent odor, and looks rather “heavy-duty.” But appearances can be deceiving—when it comes to processing precious metals and complex sulfide ores, it possesses a refined capability that xanthate cannot match.
Today, we will uncover the secrets of this “black-robed figure” in the mineral processing world—Dithiophosphate (Black Medicine).
I. What is Black Medicine? The “Wealthy Relative” of Xanthate
The scientific name for black medicine is “dithiophosphate.” Because early industrial products contained many impurities, appearing as a dark brown oily liquid, insiders commonly call it “black medicine.”
Although it belongs to the same family of sulfur-containing collectors as xanthate, the personalities of the two are distinctly different:
- Xanthate is like a “brute”: While powerful, it grabs onto any sulfide mineral it sees, easily bringing up unwanted pyrite.
- Black medicine is like a “gentleman”: Its collecting ability is slightly weaker than xanthate’s, but it is more selective and stable, and its chemical properties are more stable, making it less prone to decomposition than xanthate.
II. Its Core Specialty: Specializing in “Rich Ores”
Why is it considered so valuable? Because its tasks are all related to money (precious metals):
1. Does Not Favor Pyrite (A Natural Separation Expert)
This is black medicine’s greatest strength.
In the flotation of lead-zinc or copper-lead ores, the biggest problem is pyrite (sulfur) interfering. Xanthate collects pyrite too strongly, making separation difficult.
Black medicine, however, is almost “indifferent” to pyrite. By leveraging this property, when floating galena (lead), using black medicine allows us to collect the lead while discarding the sulfur, easily achieving “pyrite depression for lead flotation.”
2. It’s a True Fan of Gold and Silver
For ores containing precious metals like gold, silver, and platinum, black medicine’s collection effect is exceptionally good.
It forms a very strong chemical bond with the surface of precious metals. Therefore, many gold processing plants add a little 25# Black Medicine or Ammonium Dibutyl Dithiophosphate in the scavenging or cleaning stages, precisely to “extract every last bit” of gold from the tailings.
3. Self-Frothing (Dual Function)
Most black medicines (especially 25# Black Medicine) possess frothing properties.
This means that by using black medicine, you can reduce or even eliminate the need for additional frothers (like 2# Oil). The froth it produces is relatively brittle and collapses quickly, making it especially suitable for processes where sticky froth is problematic.
III. The “Three Musketeers” of the Black Medicine Family
The black medicine family has many members, but the three most commonly used are these, each with its own characteristics:
1. 25# Black Medicine (The Classic)
The most commonly used type, possessing both collecting and frothing properties. It is particularly suitable for separating lead-zinc ores or recovering copper-gold ores. Its disadvantages are its dark color, corrosiveness, and relatively strong odor.
2. Ammonium Dibutyl Dithiophosphate (The Improved Version)
This is a white powder (yes, called black medicine but it’s white). It is non-corrosive, has a mild odor, and is highly water-soluble. It is specifically used for treating silver-bearing sulfide ores and refractory copper ores, making it the preferred choice for processing plants with high environmental requirements.
3. Aniline Black Medicine (The Specialist)
This is a unique type of black medicine. It is difficult to dissolve in water but has extremely strong collecting power, specifically used to treat refractory galena that is surface-oxidized or exists as fine particles.
IV. “Mining Zones” in Application: Never Use Carelessly
Although black medicine is effective, it is known for its “irritable temper,” so caution is needed during application:
1. Pay Attention to Anti-Corrosion
Liquid black medicines (such as 25#) are acidic and highly corrosive. If accidentally splashed on the skin or spilled on equipment, the consequences can be severe. Therefore, dosing pipelines typically require special acid-resistant materials, and operators must wear protective gear.
2. Do Not Overdose
Because black medicine has self-frothing properties, if too much is added, a large amount of froth may suddenly surge in the flotation cells, leading to “cell overflows.” The dosage must be carefully adjusted in coordination with the frother addition.
3. It’s a Slow-Acting Type
Black medicine reacts more slowly than xanthate, so it typically requires longer mixing time (conditioning time) to give it ample opportunity to interact with the minerals.
V. Conclusion: The “Last Line of Defense” for Precious Metal Recovery
In today’s pursuit of refined management, black medicine is no longer just an alternative to xanthate, but rather its best partner.
The typical “golden combination” is: Use xanthate in the roughing stage for a “quick harvest” to maximize recovery, and use black medicine in the cleaning stages to “purify” and “recover gold and silver.” If your mine contains associated gold and silver, or if you are struggling with separating lead and zinc, it’s worth checking if your reagent scheme is missing a dose of “black medicine.”
Post time: Mar-25-2026
