When it comes to refining and purifying zinc products to meet the global market demand for high-purity zinc, several major considerations and processes come into play. The primary focus is on removing impurities and deleterious elements. Here are some key considerations and methods used in the refining and purification of zinc:
Roasting: The first step is often roasting the zinc concentrate, which involves heating it in the presence of air. Roasting helps eliminate volatile impurities like sulfur, arsenic, and carbon.
Leaching: After roasting, leaching is employed to dissolve the zinc oxide or other zinc-containing compounds. This process involves using an acid or alkali solution to selectively dissolve zinc while leaving impurities behind. The choice of leaching agent depends on the composition of the concentrate and impurities present.
Electrolysis: Electrolysis is commonly used in zinc refining to further purify the leach solution. The zinc-rich solution is subjected to electrolysis, where zinc is plated out on cathodes, leaving impurities in the solution or as sludge.
Distillation: Distillation is another method employed to remove impurities, particularly lead, which has a lower boiling point than zinc. By heating the zinc to a specific temperature range, the lead vaporizes and can be separated from the zinc.
Solvent Extraction: Solvent extraction techniques can be utilized to remove impurities selectively. Organic extractants or chelating agents are used to extract specific impurities, leaving purified zinc behind.
Vacuum or Thermal Treatment: Vacuum or thermal treatments can be applied to remove residual impurities and gases that may have been trapped during earlier refining processes.
Refining Fluxes: Various refining fluxes can be employed to help remove impurities during the refining process. These fluxes can react with impurities to form slag or dross, which can be separated from the purified zinc.
It's worth noting that the specific refining and purification processes employed may vary depending on the initial composition of the zinc concentrate and the targeted purity level. The selection of processes will be tailored to effectively remove the impurities and deleterious elements of concern while maximizing the recovery of high-purity zinc.