Process for Enhancing the Valuable Metal Recovery from "Electric Arc Furnace" (EAF) Slags
Résumé
Given the current depletion of the world's natural resources, the strong demand and the induced future deposit of primary mineral resources carrying metals (such as molybdenum, vanadium and chromium), one of the solution to this problem is the recycling of metals from by-products (such as steel slags) containing them. Steel slags are major by-products produced by the steel industry. Although they are considered as industrial waste that may cause public and environmental concerns, slags represent an important potential economic resource because they often contain significant amounts of valuable "Strategic Metals" (SMs). In order to minimize energy costs, environmental impacts and meet the metals demand for new high technologies, it will be more and more necessary to use cleaner and more economical technologies to recover these metals from slags. In this study, steel slags, generated from electrical arc furnace and provided by the Industeel France ArcelorMittal Company located in Châteauneuf (France), were studied. The chemical and mineralogical characterization results show that the investigated slags contain approximately 20–22% Fe, 3–4% Cr, 1 500 ppm V and are constituted of the following main crystalline phases: larnite (Ca2SiO4), magnetite (Fe3O4), wüstite (FeO) and chromite (FeCr2O4). Slag samples underwent different treatment steps before leaching (magnetic separation, grinding at d ≤ 25 μm and roasting). Various alkaline reagents (NaOH, KOH, Na2CO3 and K2CO3) have been studied with a slag/reagent weight ratio of 1, sufficiently high to provide an excess of alkaline reagent and allows the complete modification of the metal species able to be modified with these reagents at different co-grinding residence times. Three temperatures (400, 600 and 800 °C) were tested. The results show that the Cr leaching rate reaches 97.5% for one hour of the slag co-grinding with a NaOH and Na2CO3 mixture followed by roasting at 800 °C, while the V maximum leaching rate of 62.5% of vanadium is obtained after three hours of slag co-grinding with NaOH and Na2CO3 and roasted at 600 °C. The Mo leaching rate, meanwhile, reaches 95.8% using KOH for one hour of co-grinding the slag followed by roasting at 600 °C