2018 Deng Iron recovery from pyrolusite leaching slag

Pyrolusite leaching slag is a Fe-containing slag generated from the pyrolusite leaching process with SO₂. Recovery of iron from the slag not only has economic benefit, but also prevents secondary pollution to the environment. A novel lab-scale cyclic process for recovering iron from pyrolusite leaching slag was introduced. The process contains two steps: (1) iron was leached with oxalic acid and [Fe(C₂O₄)n](3−2n)+ solution was generated; (2) the [Fe(C₂O₄)n](3−2n)+ solution was irradiated by ultraviolet to obtain ferrous oxalate precipitation. The effect of operation parameters on leaching and irradiation processes were studied separately. In the leaching process, the optimal solid/liquid ratio, oxalic acid concentration, leaching temperature, stirring rate, and leaching time were determined as 1:50, 0.40 mol/L, 95 °C, 300 r/min, and 3 h, respectively. In the irradiation process, the best irradiation wavelength, Fe/oxalic acid molar ratio, and irradiation time were identified as 254 nm, 1:4, and 30 min. Additionally, a test of 9 continuous cycles was carried out to investigate the performance and material balance of the combined process. The results showed that the cyclic process is feasible and stable, producing ferrous oxalate of 99.32% purity and recovering 95.17% of iron in the form of FeC₂O₄·2H₂O with an efficiency of 58.52% for oxalic acid.