Abstract
Soil-water characteristic curve reflects water retention behavior of unsaturated soil mass. Particle size and mineral composition can influence water retention behavior of soil mass significantly. To discuss effects of particle size and solution leaching on water retention behavior of ion-absorbed rare earth, soil-water characteristic tests of samples with different particle sizes before and after the solution leaching were carried out by using a pressure plate instrument. Soil-water characteristic curves during drying and wetting were analyzed. A fitting analysis on test data was implemented by the Fredlund&Xing 3 parameter model, the Fredlund&Xing 4 parameter model, and the Van Genuchten model to discuss variation laws of soil-water characteristic parameters in different models. Effects of particle size and solution leaching on water retention behavior of ion-absorbed rare earth as well as action mechanism were investigated. Results demonstrate that given the same matric suction, soil water content decreases gradually with the increase of particle size and content of coarse particles, thus decreasing water retention capacity of soil accordingly. Given the same volumetric water content, matric suction is inversely proportional to particle size. During drying and wetting, the amplitude of variation decreases gradually with the increase of particle size and content of coarse particles. The soil water content after solution leaching is smaller than that before under the same matric suction, indicating that solution leaching can decrease water retention capacity of soil. This is mainly because thickness of the double diffuse layer and pore water pressure are increased as a response to the ion exchange, thus decreasing matric suction.
Highlights
Rare earth is adhered onto clay minerals as hydrated cations or carboxyl hydrated cations, which is called ion-absorbed rare earth [1, 2]
Solution of salt leaching agent is injected into the clay ore through the injection well, triggering chemical replacement reaction between ammonium ions in the leaching solution and rare earth ions adsorbed on the clay
During the mineral leaching of ion-absorbed rare earth, hydrated cations adsorbed on clay minerals are changed and there’s particle migration in mineral soils
Summary
Rare earth is adhered onto clay minerals as hydrated cations or carboxyl hydrated cations, which is called ion-absorbed rare earth [1, 2]. Water retention characteristics of ion-absorbed rare earth can reflect difficulties for pores in soil mass to absorb water and predict penetrating quality of ore body during in situ leaching. They are vital to improve leaching rate of rare earth [5]. During the mineral leaching of ion-absorbed rare earth, hydrated cations adsorbed on clay minerals are changed and there’s particle migration in mineral soils These changes all influence water retention characteristics of soil mass significantly. There are few studies concerning influences of solution leaching on water retention behavior of ion-absorbed rare earth. Few studies have discussed the variation law of water retention behaviors of rare earth with different particle size after solution leaching. Influences of particle size and solution leaching on water retention behavior of ion-absorbed rare earth were discussed, and the relevant influencing mechanism was disclosed
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