Waelz oxides

Type of Secondaries i Mainly Zinc dominated Battery Paste, EAF-Dust, Waelz Oxide, ... 

The ISP now accepts a wide range of secondary zinc materials including Waelz oxides, electrolytic zinc plant residues, galvanisers ashes and non-ferrous flue dusts. These materials are mainly either incorporated in the sinter plant feed or are hot briquetted and charged directly to the ISF. 

Materials that are fed via the sinter plant are mainly oxidic and there is a limit to how much can be accepted without a deterioration occurring in the performance of the sinter machine. This can be overcome to a certain extent by, for example, using clinkered Waelz oxide so that it becomes a replacement for recycled sinter fines. This means that less lunq) sinter output will need to be crushed for recycling so that the output of lump sinter increases. 

Zinc concentrate (60 wt.% Zn) is obtained by common froth flotation from run-of-mine sulfidic ores usually containing from 4 to 8 wt.% Zn. Nevertheless, it is important to note that, despite the fact that most of the concentrates used are of sulfidic origin, some oxide concentrates are sometimes also used along with recycled zinc oxide from the pyrometallur-gical pretreatment of steel, e.g., Waelz oxide. Usually, the main mineral species is zinkblende... 

Waelz zinc oxide process, 26 612 Waferboard bonding, phenolic resins in,... 

Over the period 1955-1961, the electrolytic plant processed only calcined zinc oxide having a composition of 60% Zn, 3-4% Pb and 0.03% Cd. The zinc oxide was produced by calcination of the fumes from the Waelz process at temperatures from 1420 to 1470 K. Zinc carbonate ores, Zn-Fe residues and other zinc-bearing materials were used as raw materials in the Waelz process. After enhancement of the electrolytic zinc plant in 1962, the importance of roasted sulphide concentrates was continuously growing in the feed. Currently, only the calcine from fluid-bed roasters is processed. Table I shows the analysis of the raw materials processed over the period 1998-1999. 

Electric arc furnace (EAF) dusts have become a significant source of feed for the ISP. These contain up to 35% Zn and environmental legislation in developed coxmtries is discouraging the previous practice of dumping EAF dusts. In a number of countries the Waelz process to produce zinc oxides treats these dusts. In some cases these oxides are hot briquetted as a direct feed for the ISF. An alternative method of treating steel plant and other dusts is to inject them directly into the furnace through the tuyeres. 

Waelz process. In this process, after the calcine is leached, the zinc ferrite residue is filtered, washed, dried, and heated with coke in a rotary hearth furnace. The zinc is reduced and fumed off as metallic vapor, reoxidized, and collected as a pure zinc oxide in the bag-house dust and normally leached in a separate step. Part of the lead and silver is recovered, and the iron remains in the slag. 

Waelz process A process used for the extraction of zinc and lead from ores using a rotary Idln. Zinc is still largely extracted from ores although around 40 per cent of zinc is recycled from galvanized steels and other scrap metals. A high-temperature rotary Waelz Uln is used to convert zinc dust from electric arc furnaces into zinc oxide, which is then converted to zinc metal. The process of zinc volatilization was first proposed in 1881. 

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