Magnetic Separation and Recycling of Goethite and Calcium Sulfate in Zinc Hydrometallurgy in the Presence of Maghemite Fine Particles

Abstract

Goethite (α-FeOOH) and calcium sulfate (CaSO4·2H2O) are the main solid constituents of the iron oxide residues in zinc hydrometallurgy by the goethite process. Impounding these residues in tailings ponds is costly to maintain and causes a great threat to the local environment. In this study, magnetic separation was applied to separating goethite from calcium sulfate with maghemite (γ-Fe2O3) fine particles as the carrier, which were prepared by roasting −1 μm pure magnetite mineral particles. The SEM images and XRD patterns indicated the precipitation of goethite on maghemite fine particles in the goethite process, which made the goethite aggregates magnetic, while the calcium sulfate formed nonmagnetic bulk precipitates. The magnetic goethite–maghemite aggregates were then separated effectively from calcium sulfate precipitates using a magnetic drum separator. The recovery of Fe and Ca to their corresponding products was 93.2% and 91.9%, respectively. The removal of S and As from goethite precipitates was studied by roasting with coal powder. Under the optimum conditions of the coke powder to the residue mass ratio of 4% and 1100 °C, 99.3% S and 99.5% As were removed while the goethite precipitates reached the standard of ironmaking raw materials. After drying, the calcium sulfate precipitates are used to produce cement and building materials.

Magnetic Separation of Impurities from Hydrometallurgy Solutions and Waste Water Using Magnetic Iron Ore Seeding

“…Han et al [25,[31][32] combined seed induced crystallization and magnetic separation, and proposed a novel magnetic seeding and separation process, as shown in Figure 5. Before the iron is precipitated as goethite, fine-grained maghemite or magnetite particles are added to the leaching solution to make the goethite precipitate and grow on the surface of the magnetic particles, thereby avoiding mixing with the calcium sulfate precipitation in the solution.…”

“…After the calcium sulfate precipitation is roasted, 99% of S and As can be removed, and the roasting residue can be respectively used as raw materials for ironmaking and building materials. Yue et al [31] applied magnetic iron seeding and separation to separate goethite from calcium sulfate in zinc leaching with maghemite fine particles as carrier. As is shown in Figure 6, the magnetic goethite-maghemite aggregates were separated effectively from calcium sulfate precipitates by magnetic drum separator, and 90% of Fe and Ca is respectively recovered in two corresponding products.…”

“…The formation of Fe (III) surface complexes are directly related to the nucleation and Figure 6. Schematic illustration of magnetic separation and production of desired goethite and gypsum product [31].…”

Green Recycling of Goethite and Gypsum Residues in Hydrometallurgy with α-Fe3O4 and γ-Fe2O3 Nanoparticles: Application, Characterization, and DFT Calculation

“…To recycle the goethite and gypsum mixed residues, the goethite precipitates and gypsum precipitates need to be separated first during the iron removal process, and then the hazardous elements (such as As and S) from the precipitates will be removed using reductive roasting. The treated residues can be reused as building materials, raw materials of iron-making and painting, etc. − Magnetic separation techniques have long been in use, and intensive research into superparamagnetic nanomaterials has accelerated the development of magnetically recoverable catalysts. − In our previous paper, we proposed a novel method, using maghemite fine particles as the magnetic seeds to induce the formation of goethite surface precipitates in the iron removal process, followed by separating the goethite and gypsum residues in the magnetic field and recycling these residues after As and S removal. This method can not only realize simultaneous recovery of iron and calcium but also eliminate potential environmental risks caused by the iron oxide residues.…”

“…11−13 Magnetic separation techniques have long been in use, and intensive research into superparamagnetic nanomaterials has accelerated the development of magnetically recoverable catalysts. 14−16 In our previous paper, 17 we proposed a novel method, using maghemite fine particles as the magnetic seeds to induce the formation of goethite surface precipitates in the iron removal process, followed by separating the goethite and gypsum residues in the magnetic field and recycling these residues after As and S removal. This method can not only realize simultaneous recovery of iron and calcium but also eliminate potential environmental risks caused by the iron oxide residues.…”