Gallium extraction from red mud via leaching with a weak acid

Phosphoric acid (H3PO4) was proposed to replace sulfuric acid (H2SO4) for the efficient gallium (Ga) leaching from red mud (RM). The effects of different leaching reagents were compared, and the influence of experiment conditions on the leaching was investigated. The results show that H3PO4 has the best leaching effect. The efficiency of Ga leaching was 95.9% at the leaching temperature of 100 degrees C, H3PO4 concentration of 10 mol/L, time of 6 h, liquid-to-solid ratio of 9:1, and stirring speed of 400 rpm. With H3PO4, the efficiency of Ga leaching was increased by 5% compared with the H2SO4 system. The adsorption of Ga3+ by polysilicic acid generated under H2SO4 leads to the Ga3+ entering the residue. Thermodynamic have clarified that Ga can be enriched into the leach liquor, as the leaching reaction is spontaneous. Finally, the reaction kinetic equation for the leaching process of Ga under the H3PO4 system was [(1-alpha)- 1/3-1]+ 1/3ln(1-alpha)= 203.296 C2.44exp(- 40539/RT)t. This study improves the recovery of Ga from RM. The residue can be utilized for preparing mineral fertilizers, realizing the harmless utilization of RM.