# Pyrometallurgical Technology for Extracting Iron and Zinc from Electric Arc Furnace Dust
## 4 Experimental EAFD Processing
A series of experiments allowed for determining the optimal temperature regime for melting the charge in a laboratory furnace, which ensured the sequential flow of all physicochemical interactions occurring in the granulated pig iron production: feeding the charge at 1150 \({}^{\circ}\)C, raising the furnace temperature to 1350 \({}^{\circ}\)C at a rate of 15 \({}^{\circ}\)C/min, increasing the furnace temperature to 1425 \({}^{\circ}\)C at a rate of 11 \({}^{\circ}\)C/min, and decreasing the furnace temperature to 1150 \({}^{\circ}\)C at a rate of 30 \({}^{\circ}\)C/min. The captured gaseous reduction melting products was removed through a pipe from the upper part of the furnace's working chamber by induced draft. The sublimed products entered the water-cooled gas flue, where the gas stream cooling, condensation, and partial precipitation of sublimates took place. Dust residues were captured by passing the dust-gas flow through a water filter in the form of a flask with water. The reduction melting of the pelletized charge formed slag granulated pig iron. Shock cooling of this product in water leads to the instantaneous crystallization of iron particles and their separation from the slag. The granulated pig iron particles obtained (Figure 6) were 10-15 mm in size and had magnetic properties. The extraction of iron into pig iron was 92-96%. Figure 5: Laboratory EAFD processing unit: 1—crucible with charge; 2—furnace; 3—flue; 4—water-cooled jacket; 5—water trap for dust; 6—vacuum pump. Three samples were taken to define the chemical composition of the pig iron produced. The chemical analysis of inclusions was performed by electron probe microanalysis (EPMA) using an X-ray wave spectrometer and a KEVEX energy-dispersive spectrometer. The study results are given in Table 6. Figure 7 shows the distribution of the selected elements in the characteristic X-rays. A metallographic study was performed to determine the microstructure of the obtained pig iron samples. The studied thin sections (after etching with a 3-5% nitric acid solution) were analyzed using an Olympus GX-51 electron microscope (Olympus, Tokyo, Japan). It has been established obtaining the hyper eutectic white pig iron, the structure of which is represented by per \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Elements** & **Fe** & **C** & **Si** & **S** & **Ni** & **Cu** \\ \hline Value, wt\% & 95.01–95.5 & 4.2–4.6 & 0.1–0.13 & 0.05–0.09 & 0.06–0.07 & 0.09–0.1 \\ \hline Average value, wt\% & 95.27 & 4.4 & 0.11 & 0.07 & 0.06 & 0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The chemical composition of pig iron samples. Figure 6: The granulated pig iron samples. Figure 7: The EPMA results: (**a**) iron; (**b**) sulfur; (**c**) silicon. Zinc sublimates caught in different deposition areas of the dust collecting system were mixed to obtain an average product sample, the chemical composition of which was defined by XRF. According to the data obtained, the major compound in the sample is ZnO with a content of 68.8 wt%; the presence of chlorine and fluorine was also recorded with a content of, respectively, 5.32 and 1.31 wt%. Calcination at 1000 \({}^{\circ}\)C for 90 min was proposed to remove halogens. The chemical composition of ZnO after calcination (Figure 9) is given in Table 7, which allows for concluding that the resulting product is suitable for further use. The obtained zinc-containing powder consists of 80% of particles with a size of 20-30 \(\upmu\)m.  
A process flowsheet for the EAFD processing (Figure 10) has been developed and proposed based on the laboratory study results. The basic unit in this technology is a rotary hearth furnace. The proposed technology of EAFD processing consists of the recovery of iron and zinc from their oxygen-containing forms by active carbon-containing materials in a rotary-hearth furnace [27; 28]. The biriquettes charge includes oxide scale, EAFD, long-flame little nut (DOM) coal, lime, and molding sand.