Inhibition on the swelling of clay minerals in the leaching process of weathered crust elution-deposited rare earth ores

Rare earths are mainly adsorbed on the clay minerals as ion-exchangeable phase which could be extracted by the ion-exchange method in weathered crust elution-deposited rare earth ore. The clay minerals would swell after adsorbing electrolyte solution during the rare earth leaching process, which would easily lead to the occurrence of landslides and other geological disasters. In this study, to alleviate the expansion of the clay minerals, swelling kinetics curves of the ore samples in the three anti-swelling agents: urea, NH4Cl and NH4NO3 were investigated. Synergy effects of these three anti-swelling agents in binary and ternary systems were also studied. Results showed that the lowest swelling ratio was obtained in the urea/ NH4Cl/NH4NO3 system: 3% wt NH4Cl and NH4NO3 with mass ratio: 7:3 and 6% wt urea at the optimum value of pH 5.0. The Swelling ratio of clay minerals increased with the increase of the temperature in the ternary system. Additionally, swelling kinetics equation δ = A•e-B/t of the clay minerals in different anti-swelling agents were also determined by mathematical regression analysis. The SEM, TG, FTIR and XRD analysis of rare earth tailing leached by ternary system verified the anti-swelling function of urea in the leaching process.