The Feasibility of Using Jarosite Waste From the Zinc Industry for HIsarna Ironmaking

Abstract

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.