Low Grade zinc Oxide Ore Enrichment
Zinc oxide ore is an important industrial mineral containing zinc, a trace element for many different applications, including galvanizing and the production of various alloys. Zinc oxide ore is typically composed of 15-20 percent zinc and the greatest challenge in beneficiating zinc oxide ore is achieving high recovery while maintaining grade. The key factors on which it depends are the size of the ore pieces to be treated and the complexity of the ore.
While the majority of zinc oxide ores are low grade (contains zinc grades of 10-20%) and sulfur rich. The recovery of zinc oxide is low due to high grade losses in the separation process. The high grade losses occur mainly due to the small particle size of zinc minerals and most of the particles have sulfides containing zinc in them, which makes them difficult to recover in traditional separations.
To overcome this, several zinc oxide beneficiation techniques are in practice such as froth flotation, selective leaching, selective flocculation etc. Flotation is the most widely used technique, which relies upon the difference in density between the mineral particles and the gangue materials, allowing the concentrations of organic (collectors) being added to the slurry to selectively bond to the particles of interest. Different types of collectors may be used based upon the other impurities present in the ore.
Froth flotation is commonly used to separate the zinc oxide ore from the gangue containing sulfides or other compounds. The process typically involves the addition of a reagent, called a depressant, which often contains anionic agents and may also include a neutralizing agent such as a phosphate. The depressant also helps to form a froth, and the froth is skimmed off the top of the flotation cell and collected.
These froth flotation products can then be further processed by selective leaching. Selective leaching involves using an acidic or a basic reagent, such as ammonium hydroxide, to selectively leach out the zinc in the ore. The zinc-rich solution is then recovered and may be further concentrated or treated for extraction of the desired metal. Another method that is utilized in zinc oxide ore enrichment is the application of selective flocculation. This technique involves the introduction of polymers, which when added to the ore suspension, form flocs at a certain particle size range. This allows larger zinc particles to be removed from a suspension, while the smaller particles remain suspended in the solution.
In addition to these conventional methods, advanced hydrometallurgical techniques such as bioleaching, solvent extraction and electrochemical techniques have also been investigated for zinc oxide ore enrchment.
Bioleaching involves the addition of certain bacteria, which oxidize the zinc oxide ore in order to release the soluble zinc levels into the leaching solution. The leaching solution is then recovered, treated for the extraction of the desired metal and further processed for reuse. Solvent extraction process involves the use of a specific solvent, usually an aliphatic ketone such as acetone or methyl ethyl ketone to extract the required metal from zinc oxide ore. Lastly, electrochemical techniques, such as electrolytic or electrodeposition, may also be used for zinc oxide ore beneficiation.
Collectively, these processes reduce the costs associated with transportation, roasting and smelting by improving the grade of zinc oxide ore that is mined. All of these techniques are promising methods of zinc oxide ore enrichment and will be increasingly important as the demand for zinc continues to grow.
