# Evaluation and Current State of Primary and Secondary Zinc Production--A Review
## 4 Zinc Production from Secondary Resources
\begin{table}
\begin{tabular}{c p{284.5 pt}} \hline \hline
**Process** & **Characteristics** \\ \hline Molecular Recognition (MRT) & The first commercial hydrometallurgical process for the treatment of EAF dust was launched in the USA (1995); the dust is leached with hot ammonium chloride to dissolve most of the zinc, lead and cadmium oxides in the dust; the teach slurry is filtered and unleached iron oxide containing zinc ferrite is filtered, washed and returned to the smeller or landfilled; the leaching solution is treated with zinc dust to precipitate the dissolved lead and cadmium as a precipitate, which is further separated into metallic lead and cadmium for sale; the pure solution goes to the crystallizer, where high-purity zinc oxide crystals are produced; the ammonium chloride solution is concentrated and recycled to the leaching process. \\ \hline EZINEX & Process at Osoppo, Italy (since 1996), EAF dust is leached with ammonium chloride solution to dissolve Zn, Pb and Cd oxides; the leaching solution is filtered and treated with Zn powder to precipitate lead and cadmium; zinc is electrolytically separated from the purified solution, the spent electrolyte is recycled to the leaching stage; Fe-rich leach residue is dried, granulated with coal and recycled to EAF; no other by-products. \\ \hline CASHMAN & A process adapted by American Metals Recovery Corp. for the purification of EAF dust, zinc which is not present in zinc ferrite is leached under pressure in a CaCl\({}_{2}\) solution; the leached solution is purified by precipitation using Zn dust to remove lead and cadmium; high purity ZnO precipitates from the purified solution; leaching residue is processed to recover residual zinc and produce iron-rich residue, the process uses pressure leaching, but zinc recovery is not very high. \\ \hline Waelz process & The rotary kiln process for processing zinc dust is most often carried out in Waelz furnaces; zinc waste can be separated from iron due to high zinc vapor pressure. \\ \hline Electroothermic Retort Processes & Developed by St. Joseph Mineral Company (in 1930), the possibility of smelting a wide range of zinc-bearing materials, including EAF dust, less efficient than hydrometallurgical processes, electrical resistance type furnaces are used in the process; the flow of current through the sintered ore and the coke charge generates the energy needed to melt them, the Zn vapors pass into the vacuum condenser, where zinc is obtained. \\ \hline Zincex & A hydrometallurgical process using atmospheric leaching, solvent extraction and an electrolysis process, modified in the early 1970s, aimed at recovering Zn from complex Zn solutions with a high presence of impurities that are difficult to separate by conventional methods, it is now used commercially to process oxide ore Zn in Skorpion (Namibia), recycled in Akita (Japan), in Portovesme (Italy) and in Horsehead (USA). \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Characteristics of metallurgical methods for processing secondary zinc waste [77; 79; 80; 81; 82].