Recovery of niobium and tantalum from tin slags: An alternative approach using acid roasting and oxalic leaching

Abstract

An alternative approach for extracting Nb and Ta was investigated, based on the acid roasting of tin slags using the KHSO₄-H₂SO₄ system, followed by oxalic leaching. Roasting experiments demonstrated the formation of soluble sulfated products, optimized through thermodynamic modeling: mineral grain size fraction −75 µm, Slag-KHSO₄-H₂SO₄ ratio 1:0.5:0.5 (g:g:ml), roasting temperature 300 °C, and roasting time 2 h. Under these conditions, the material conversion rate was maximized, characterized by mineralogical and morphological analyses that showed the chemical changes occurring during roasting helped explain the mechanisms at work during the process. After optimizing the treatment parameters by varying process conditions, it was found that approximately 94 % of Nb and 75 % of Ta were dissolved during the oxalic leaching stage, under the following conditions: concentration 0.5 mol L⁻¹, S/L ratio 50 g L⁻¹, reaction temperature 60 °C for 60 min. Consequently, this innovative alternative could reduce reagent and energy consumption, promoting a sustainable approach with a lower environmental footprint.