# Evaluation and Current State of Primary and Secondary Zinc Production--A Review
## 3 Zinc Production from Primary Resources  
Of the many zinc minerals, only a few are of economic importance. Currently, up to 85% of all zinc production uses sphalerite (ZnS). Its world reserves are enough for several decades. Zinc oxide minerals are zinc carbonates, including smithsonite and hydrozincite and the zinc silicates hemimorphite and willemite. Zinc oxide ores are generally less of a metallurgical and environmental problem than zinc sulphide ores due to the absence or relatively low amounts of elements such as arsenic, cadmium, lead and sulfur. Due to the depletion of sulphide ores and the reduction of sulfur emissions during the technological process, there is an increasing interest in oxide ores, e.g., carbonates and silicates [52; 53]. The first stage of obtaining zinc from such ores is the production of a concentrate by flotation or by gravity method. If sulphide or oxide raw materials are processed, an average SO\({}_{2}\) content of 5% is obtained in the waste gases, and these gases are used in the sulfuric acid plant. When processing oxide-type raw materials, the SO\({}_{2}\) content in the flue gas is too low (0.3-0.5 wt.%) to be used in the sulfuric acid plant, so the gases must be treated in a different way. The next stage is the processing of the concentrate by pyrometallurgical or hydrometallurgical means. The use of the pyrometallurgical path is not suitable for the processing of low-grade oxide ore due to environmental pollution, high capital expenditures and significant energy consumption [54; 55]. Pyrometallurgical methods have various disadvantages, including high energy consumption, significant capital investment and the production of harmful greenhouse gases. The advantage of hydrometallurgical processes is that, on a small scale, the process can be economical due to low capital and operating costs and the recovery of valuable metal-containing products. In addition, the hydrometallurgical processing of zinc minerals has some environmental benefits. Figure 6 presents the available methods of processing zinc ores in the world, while Table 5 presents the characteristics  
Figure 5: Zinc end use by applications in 2018, figure prepared based on data taken from [50; 51]. of the main processes used for the processing of zinc ores. Primary zinc is supplied to the market in various qualities, with the highest quality being special high-grade (SHG) zinc or Z1, which contains 99.995 wt.% zinc, followed by Z2 (99.99 wt.%), Z3 (99.95 wt.%), Z4 (99.5 wt.%); while the lowest quality good ordinary brand (GOB) or Z5 is around 98.5 wt.% purity. In addition, this zinc contains such impurities as Pb up to 1.4 wt.%, Cd up to 0.005 wt.%, Fe up to 0.05 wt.%, Sn up to 0.001 wt.%, Cu up to 0.002 wt.% and Al up to 0.001 wt.%. Simultaneously, secondary zinc grades are divided into the following three categories: ZSA (obtained mainly by zinc-bearing process scrap, e.g., Zn ashes)--98.5 wt.% with impurities such as Pb (1.3 wt.%), Cd (0.02 wt.%), Fe (0.05 wt.%) and Al (0.05 wt.%); ZS1 obtained mainly by recycling of scrap containing 98 wt.% Zn and ZS2 containing 97.5% Zn. Figure 6: Available methods of processing zinc ores, figure prepared based on data taken from [56; 57].