Depressants such as Sodium Metabisulphate and Sodium Cyanide prevent collectors from adsorbing onto a mineral.

Make An Enquiry


  • Facilitate the separation of sulfide ores.
  • Prevent collectors from adsorbing onto a mineral.
  • Can be used to depress Zn sulphide, Fe sulphide and other minerals.

Depressants facilitate the separation of sulfide ores either by depressing gangue minerals and floating the desired mineral, or by holding down the desired mineral while floating the undesirable gangue.

It is important to note that just because a reagent is a depressant for one mineral/collector combination, it does not necessarily follow that it is a depressant for other combinations.

Depressant applications

These depressants are shown with their typical applications:

Sodium Metabisulphate – Depression of Zn sulphide (sphalerite) and Fe sulphide (eg. pyrite, pyrrhotite) minerals.

Sodium Sulphide / Sodium Hydrosulphide – At low dose rates (below 500 g/t), can be used as to depress Zn sulphide (e.g. sphalerite) and Fe sulphide (e.g. pyrite, pyrrhotite) minerals. At high dose rates (above 500g/t), it can be used to depress all sulphides (reverse flotation), allowing gangue to float and be removed.

Sodium Cyanide – Strong sulphide depressant for iron and zinc sulphides (e.g. pyrite, pyrrhotite, marcasite, arsenopyrite, sphalerite).

Lime – Depressant for pyrite during copper and zinc flotation and in other sulphide ores where pyrite is a problem.

Carboxymethyl cellulose – Depression of silicate gangue (e..g. talc, serpentine, lizardite, antigorite)

Guar Gum – Depression of silicate gangue (eg. talc, serpentine, lizardite, antigorite)

Zinc Sulphate – Depression of zinc sulphide from lead and copper sulphide minerals. Can be used alone or in conjunction with cyanide.

Dextrin – Mostly used to depress carbon minerals during sulphide flotation. Can also been used to depress galena.

Related Products & Services

Unlock your full potential

Take your operations to the next level by exploring these additional products and services.


Regrind Balls

process optimisation


Related Resources



Molycop manufactures frothers, collectors and modifiers that aid the extraction of valuable minerals.

Read More
Fosterville Gold Mine: Successful Deployment of Milling Optimisation Technology

Fosterville Gold Mine: Successful Deployment of Milling Optimisation Technology

Agnico Eagle Fosterville Gold Mine (Fosterville) operates a gold plant in Australia comprising of a crushing and grinding circuit (SAG mill with a closed loop cyclone classification circuit) followed by flotation, bacterial oxidation and leaching circuits. The lack of surge capacity between the grinding and flotation circuit and restrictions on crushing operations due to noise constraints resulted in unique set of challenges, that required the implementation of a novel control solution using advanced instrumentation.

Read More


At Molycop, we see innovation as a way to find solutions to some of the mining industry’s greatest challenges. We aim to improve on today so we can deliver better for tomorrow.

Read More


Molycop manufactures and distributes a wide range of flotation chemicals and instrumentation that can be tailored to suit your requirements and maximise your recovery.

Read More

Cookie Settings

We use cookies, including third party cookies, for operational purposes, statistical analyses, to personalize your experience, provide you with targeted content tailored to your interests and to analyze the performance of our advertising campaigns.

To find out more about the types of cookies, as well as who sends them on our website, please visit our dedicated guide to managing cookies.