Swelling of clay minerals during the leaching process of weathered crust elution-deposited rare earth ores by magnesium salts

Abstract

To ensure the safety of leaching process in the weathered crust elution-deposited rare earth ore, it is of great importance to decrease the swelling of clay minerals in the rare earth ore for preventing landslides and other hazards. Meanwhile, it is also necessary to ensure the leaching efficiency of rare earth ores during industrial production. In this study, the effect of the magnesium ion concentrations and acidity of magnesium salts on the swelling process was investigated. The inhibiting properties of the optimized magnesium salts were evaluated by anti-swelling experiments. The results show that the relation between the linear swelling ratio of the clay minerals and time correspond with the equation δ = A·e-B/t when the rare earth minerals were recovered from weathered crust elution-deposited rare earth ore with magnesium salts. The optimal leaching conditions were determined to be 0.2 mol/L of magnesium nitrate with a pH below 6.0, with the kinetic equation: δ = 1.5995·e-5.5170/t. According to the evaluations, magnesium nitrate shows a strong capacity to inhibit the hydration swelling and dispersion of clay minerals at room temperature; the anti-swelling rate of 0.2 mol/L magnesium nitrate was 65%, the highest among the magnesium salts. Decreasing the pH and leaching temperature of the magnesium salt solution could effectively reduce the swelling of clay minerals during leaching. The results of the experiment could lead to an improvement in the in-situ leaching technology and reduce the risk of hazards, which has a significant meaning in the safe operations of the mining process.