1. Tannins in Mineral Processing
Jordan Rutledge & Dr. Corby Anderson
Colorado School of Mines
Introduction
Flotation
Precipitation
Future Work
What are tannins?
Tannins are an organic compound that is composed of a varying number of phenols. Phenols are made up of the phenyl and hydroxyl groups and have the molecular formula of C6H5OH. Tannins are found in many natural objects like bark, trees, and leaves. It is also in many foods such as grapes, blueberries, tea, chocolate and corn. [1]
Figure 1 & 2. Chemical 2D and 3D structure of quebracho. [2]
History and Applications
Tannins have been widely used for a very broad range of applications for centuries. Generally, the first use that comes to mind is leather tanning or tannins in wine production. However, there is also a great potential for use of tannins in industrial applications. Quebracho is a type of tannin that is derived from the quebracho tree that is particularly useful. Quebracho comes from a tree that is only present in certain climates and areas in the world. Argentina hosts much of these quebracho forests. This tannin has shown promise in many different industrial applications. It has been used the oil and gas industry for over 60 years as a dispersant and deflocculant for drilling mud, as a dispersant in the chemical industry and as a depressant for mineral flotation.
Figure 3. Additives being combined with drilling mud. [3]
Quebracho is most commonly used within industry as a method to separate out fluorite from calcite, which is traditionally quite challenging as both minerals share a common ion—calcium. Other applications for quebracho in flotation with calcite minerals as the main gangue source include barite and scheelite. In sulfide systems, quebracho is a key reagent for differential flotation.
The depressing action of quebracho on metallic sulfides is as follows: Fe > Zn > Pb > Ag > Cu. [4]
This indicates that selective flotation of copper can be obtained from a polymetallic sulfide ore through the use of quebracho. A benefit of this approach is that value added side products, specifically silver and gold, additional report to the concentrate, providing further value to the sulfide ore. In the case of using quebracho over other reagents, it is of particular interest for several reasons. Quebracho is relatively cheap in comparison to synthetic reagents that have a comparable depression effect. Quebracho is also completely non-toxic and operates best in systems with pH around 6-8, which is a positive for treatment and environmental concerns.
Gold
One intriguing precipitation method is applied at the Fosterville Mine in Victoria, Australia, which treats primary sulfide refractory gold ore by means of bacterial oxidation, cyanidation, and froth flotation. While the majority of gold remains in the solids, part of it is lost to the waste liquor stream. Tannins were used to form fine precipitates from the soluble iron in the liquor and thus created a large surface area for the collection of the ultrafine gold. With the implementation of tannins into the circuit, the overall gold recovery in the Fosterville plant has increased by 2.6 percent. [5]
Figure 5. A quebracho colorado tree.
Mineralogical/ chemical characterization
XRD & QEMSCAN
ICP MS
Fundamental surface chemistry
Zeta potential
Contact angle
Adsorption density
Mineral processing
Micro flotation
Flotation (mechanical and column)
Precipitation
Economics
Table 2. Applications that quebracho could be used to depress either calcite or pyrite from varying minerals. [5]
Tannins (g/L)
Gold loss (%)
0.0
5.0
0.4
2.1
0.6
1.1
Germanium
In addition to gold precipitation, experimentation has been done for the use of tannins for germanium recovery from zinc production byproducts. The recovery of germanium from Cu-Pb-Zn ore was studied at the Cinkur Zinc Plant in Kayseri, Turkey. The tannin precipitation study indicated that 94% of the germanium could be selectively recovered from leach solution. [6]
Table 1. Applications that quebracho could be used to depress either calcite or pyrite from varying minerals.
References
Calcite
Pyrite
Fluorite
Chalcopyrite
Barite
Chalcocite
Scheelite
Galena
Manganese Oxides
Sphalerite
Cassiterite
Argentite
[1] A. Cannas, 'Tannins: fascinating but sometimes dangerous molecules', Cornell University: College of Agriculture and Life Sciences, [Online]. Available: [Accessed: 13- Feb- 2015].
[2] Pubchem.ncbi.nlm.nih.gov, 'Quebracho | C26H20O18 - PubChem', [Online]. Available: [Accessed: 13- Feb- 2015].
[3] M. MH1 Web Design, 'Drilling pit engineers, drilling fluid materials, drilling operation engineering | Conquest Drilling Fluids', Conquestdrilling.com, [Online]. Available: [Accessed: 13- Feb- 2015].
[4] Iskra and Kitchener, 'Quebracho in Mineral Processing', Imperial College, 1973.
[5] R. Symes, 'Recovery of Colloidal Gold from Oxidised Concentrate Wash Liquor', Tenth Mill Operators Conference, 2009
[6] M. Kul and Y. Topkaya, 'Recovery of germanium and other valuable metals from zinc plant residues', Hydrometallurgy, vol. 92, no. 3-4, pp , 2008.
[7] V. Pillar, ‘Desmonte quebracho colorado.’ 2005.
Figure 4. Flowsheet for Cinkur zinc plant. [6]