Crude zinc oxide (C.Z.O.) is one of the important resource of zinc metal extraction. The main source of crude zinc oxide includes: a. zinc dust collected from EAF (electrical arc furnace); b. fume dust collected from zinc leaching residue treatment by waelz kiln; c. zinc fume dust collected from lead slag treatment by fuming furnace; d. zinc skim from steel galvanizing/plating process. 

Generally, standard crude zinc oxide usually contains impurities like fluorine and chlorine, which are harmful substance and have to be removed before zinc electrowinning. The common equipment for deflourination and dechlorination is multiple-hearth furnace. The multiple-hearth furnace works with certain negative pressure under which the low boiling point matter like fluoride and chloride evaporates and is directed to the flue gas system. This method is relatively effective and has been applied by many plants.

However, recent tendency shows more chlorine and fluorine comes to zinc smelting system from zinc concentrate, imposing great challenges on multiple-hearth furnace treatment.

Metalcess offers ammonium leaching + zinc electrowinning to treat high fluorine and chlorine- bearing crude zinc oxide. With ammonium leaching, zinc oxide, copper, cadmium, cobalt, nickel and silver dissolve into the solution while lead, iron and magnesium remain in the leaching residue. The solution is further purified by adding zinc powder to replace the other metal impurities like copper, cadmium, cobalt, nickel and silver. The solution goes to electrowinning to deposit zinc cathode.

Characteristics

1. Cell voltage 2.6-2.9V, current efficiency larger than 93%, direct current power consumption of zinc electro-winning: 2300-2600Kwh/t

2.  No need of defluorination and de-chlorination treatment;

3. No need of iron removal as the iron doesn’t dissolve in ammonium solution;

4. High purity zinc ingot production;

5. Less complicated process for easy control, the system works well even with high purity in solution

6. Environmental-friendly production process, no waste water disposal;

7. Favorable to valuable metal recovery (copper, lead, except Indium).