Hydrogen as Carbon-Free Reducing Agent in Non-ferrous Slag Fuming

Abstract

In this work, pyrometallurgical treatment of non-ferrous iron residue was studied. This approach aimed to recover the valuable metals and convert the residue into reusable benign slag using hydrogen as a non-fossil reducing agent. The pyrometallurgical treatment for this type of residue involves pretreatment prior to two stages, oxidation and reduction. Hydrogen was employed as a reducing agent in slag cleaning. The reduction tests were performed at temperatures of 1200 °C, 1250 °C, and 1300 °C using H2 and N2 gases to form the reducing gas atmosphere. The results show that H2 is an effective reductant because reduction proceeded rapidly, forming speiss droplets within the slag already after 10 minutes. The laboratory-scale experiments suggest that slags or other residues obtained from metallurgical processes can be further cleaned in a fuming process using hydrogen and its mixtures to obtain environmentally friendly cleaner slag with respect of volatile metals. The results also show that one can tune the reduction and control the formation of metallic iron during the process. Thermodynamic modeling was also performed to simulate the fuming stage, i.e., reduction of the slag. Metal alloy formation as well as elemental distributions between metal and slag were studied, and results from thermodynamic modeling agree well with experimental results.

Processing of a Zinc Leach Residue by a Non-Fossil Reductant

“…However, the reduction had not been sufficient because plenty of solid particles were still present in the slag matrix and had not dissolved in the slag as FeO. In a previous study, where the jarosite residue was treated using hydrogen as a reductant, the reduction had clearly proceeded further because the slag matrix was mainly free of iron oxides after only a 15 min reduction . The presence of incompletely reduced iron oxides in the slag matrix is considered detrimental because they increase the viscosity of the slag so that metal droplets tend to attach to them, possibly preventing the formation of a larger metal phase or hindering their volatilization to the gas phase.…”

“…The efficiency of zinc fuming with biochar in the pyrometallurgical treatment of the jarosite residue has been evaluated with a simple thermodynamic simulation, showing that only 10–30% more biochar is needed compared to the amount of coke required to achieve the typical recovery rates of zinc (> 90%) . No previous experimental studies regarding the use of biochar in pyrometallurgical processing of jarosite residues were found; however, high-temperature reduction of the calcinated jarosite residue has been studied on a laboratory scale using hydrogen as a non-fossil reducing agent …”

“…6 No previous experimental studies regarding the use of biochar in pyrometallurgical processing of jarosite residues were found; however, high-temperature reduction of the calcinated jarosite residue has been studied on a laboratory scale using hydrogen as a non-fossil reducing agent. 7 Over the last few years, the annual total amount of zinc production worldwide has been about 13−14 Mt, 8 of which the vast majority, about 85%, is produced by the roasting− leaching−electrowinning (RLE) process. 9 To produce highquality (99.995%) zinc by hydrometallurgical processing, the formation of an iron leach residue is inevitable, and iron removal from the leaching solution is needed before electrowinning.…”

“… 6 No previous experimental studies regarding the use of biochar in pyrometallurgical processing of jarosite residues were found; however, high-temperature reduction of the calcinated jarosite residue has been studied on a laboratory scale using hydrogen as a non-fossil reducing agent. 7 …”

Development and application of matte/speiss/metal thermodynamic database for optimization of processing of drosses, dusts and reverts from lead, zinc and copper production

“…Typically, solid speiss compounds are considered as undesirable by-products and very few companies are willing to treat them to extract metals. Other areas of potential speiss formation in Figure 1 are: Fe-As and Zn-As compounds in the products of corrosion of steel jackets in the "Pb blast furnace" [25], droplets of Cu-As, Cu-Sb, and Fe-As in the slag of "Zn fuming [26].…”