Extraction of zinc falls into two groups, pyrometallurgy and hydrometallurgy. Zinc pyrometallurgy has different methods by using different equipments like horizontal retorts, vertical retorts, enclosed blast furnace and electric furnace. Zinc hydrometallurgy includes zinc conventional/ pressure/hot acid leaching + jarosite/ goethite/ hematite precipitation + zinc electrowinning. Process selection depends on the ore concentrate property, local energy supply and water supply. Iron is the major inclusion of zinc concentrate. Whatever the approach is, high iron content in less amount slag/residue with easy separation and less zinc loss is preferred. Apart from economic indicators, environment requirement and energy consumption are factors taken into consideration. 

In terms of zinc pyrometallurgy, horizontal and vertical retorting has been abandoned due to its high energy consumption, low recovery rate and environment pollution. The other three processes used in existing smelters account for only about 15% of global zinc production.

1.    Imperial Smelting Process (ISP) uses enclosed blast furnace to treat zinc lead complex ore. Zinc vapor is released from the top of the furnace while lead is discharged from the furnace bottom. ISP technology had fast development in 1960s-1970s. Due to its high energy consumption and improvement of zinc & lead concentrate separation technology, ISP has lost the advantage to zinc hydrometallurgy. 

2.    Zinc electric arc furnace smelting takes classified sintered ore and coke as raw material to produce zinc vapor. Zinc vapor discharged from the furnace top to a zinc spray condenser to get crude zinc. This crude zinc is distillation refined to high purity zinc and valuable metal like indium, germanium, and silver. Lead are enriched in the distillation residue (hard zinc). The hard zinc is further treated by vacuum distillation to recover valuable metals. In this process, more than 90% indium are captured in zinc vapor and the recovery rate of indium reaches 80%. Electricity consumption of zinc electric arc furnace ranges from 3500-4300kw.h/t crude zinc, depending on the zinc concentrate grade. Compared with vertical retorting process, zinc electric furnace smelting has better adaptability to raw material, especially to high copper-iron-silica zinc concentrate, and higher metal recovery rate. Low investment, short process, easy operation, high direct recovery rate and controllable environment pollution encourage its application in the area with zinc ore and sufficient power supply.    

 

Development of Zinc hydrometallurgy follows the success application of iron precipitation like jarosite and goethite process, which enables zinc acid leaching to be a feasible solution. Introduction of this part please refers to zinc leaching and purification. 

Metalcess developed flash magnetization roasting technology in the aim to recycle goethite generated in the iron removal process of zinc leaching. It can  enrich the goethite residue into standard iron ore for sale. It is the best accessible green solution to recycle iron at high efficiency but low cost.

 

Metalcess also provides solution to treat zinc leaching residue so as to recover lead and silver. By fuming with side-blowing furnace, the final residue as fuming slag are non-hazardous waste suitable for landfilling.