Jarosites are an Fe-rich waste product from the Zn industry. They contain toxic heavy metals like Pb, Zn, Cu, Ni, and are consequently disposed of in regulated ponds. With Zn demand projected to continually increase in the future, it is anticipated that by 2023, the Fe content in these jarosites will amount to 2.2 million tonnes/year. With the advent of the circular economy and raw materials scarcity it has become imperative that ’wastes’, like jarosite, are converted to resources. Since jarosites are Fe-rich, they can be used for ironmaking. HIsarna is a revolutionary ironmaking process that has greater flexibility in the raw materials it uses. It can potentially utilise jarosite, which was unsuitable for a conventional blast furnace, to make hot metal. However, steelmaking, which occurs downstream of HIsarna ironmaking, requires the removal of Cu, Ni, Cr, Sn and Mo (termed CEF metals). Removal of these CEF metals, particularly Cu, from jarosite whilst fixing sulfur is necessary before it is acceptable for HIsarna. This thesis evaluated several metallurgical approaches in removing the CEF metals from a locally sourced jarosite whilst fixing sulfur. The jarosite was sourced from Nyrstar (Budel, Netherlands) and is commercially known as Budel Leach Product (BLP). The BLP had a CEF concentration of 1.8 wt% which was substantially higher than the HIsarna limit (0.2 wt%); it also had a sulfur content of 9.3 wt%. The metallurgical approaches taken to treat the BLP included: hydrometallurigcal (acid, alkaline. ammoniacal and DES leaching); pyrometallurigcal (thermal decomposition and chloridisation); and a combined pyro- and hydrometallurgical approach (sulfur fixation with Na2CO3 with water washing). Ammoniacal leaching was the most effective hydrometallurgical approach in selectively removing Cu from the BLP, however, leaching efficiencies were low. Thermal decomposition resulted in an upconcentration of the CEF metals whilst releasing SO2 . Sulfur could be fixed with the combined approach, however, the presence of Na2CO3 converted any soluble CEF metal sulfates to insoluble oxides which increased CEF concentration. The most effective approach was the chloridisation of BLP which reduced the CEF concentration in the treated residue while fixing sulfur. Although the CEF concentration using the chloridisation approach (0.84wt%) was above the HIsarna limits, further refinement of the treatment strategy shows promise for utilising BLP in HIsarna ironmaking.

HIsarna is a new furnace technology in the steel industry, featuring a large reduction of CO₂-emissions of up to 80%, and offering larger tolerances for gangue materials. Additionally, it has potential for zinc enrichment in the flue dust, as it can quickly vapourise zinc in the feed material and reject it to the flue dust. Increasing the zinc fraction in the flue dust up to 50% would allow for zinc recovery in the zinc smelters. The larger tolerances of the furnace make it possible to include material streams currently mostly land filled. In this thesis, the focus has been on three of these waste streams, goethite, Blast Furnace (BF) dust, and Basic Oxygen Furnace (BOF) dust. The research focussed on acquiring fundamental knowledge on the behaviour of these waste dusts at high temperatures and various retention times. This will aid their future use as an alternative feed stream material for enriching the HIsarna flue dust with zinc, without compromising the longevity of the furnace or the quality of the steel.
In a literature study, several alternative materials were investigated. Of particular interest are the sludge wastes from the steel industry for their large iron and zinc contents, the sludge waste from the zinc smelters for the same reason, and galvanised steel scrap, possibly in combination with EAF dust. There are a few challenges to overcome, such as the copper concentration in the zinc smelter residues, or the variation in composition and quality of steel scrap. However, these materials were identified as high potential for inclusion in HIsarna.  It was found that zinc can effectively be reduced and vapourised from the waste dusts regardless of its mineral form, in case there is carbon. The carbon acts as a reductant for the iron oxides, including zinc ferrite, and for zinc oxide. Goethite does not contain any carbon, however, mixing with BF sludge will allow the vapourisation of zinc. A model is proposed for estimation of the amount of carbon, and by extension BF dust, that is needed to achieve a full reduction of the iron oxides with native carbon sources. This will aid future mixing of these waste streams, allowing more control over the composition of the feed stream.
A competing mechanism to direct reduction of zinc oxide was identified. Zinc oxide can react with S₂ gas which forms during the thermal shock treatment, forming a zinc sulfide fine particle. At high temperatures, this intermediate species decomposes over time to release the zinc vapour, however, the exact mechanism could not be deduced from the experiments. The mechanism and timescale was verified at various temperatures, and holds up until 1300 ºC. The timescale shortens significantly when increasing the temperature. Therefore, from the work conducted, it was concluded that the zinc can be effectively removed at a relevant timescale for HIsarna and collected in the flue dust.