Swelling inhibition and infiltration promotion mechanism of polyethyleneimine

In order to solve landslides and slow infiltration rate in in-situ leaching process of weathered crust elution-deposited rare earth ore (WCE-DREO), the swelling inhibition performance and mechanism of polyethyleneimine (PEI) on montmorillonite (MMT) and WCE-DREO were investigated. The swelling inhibition effect on MMT and WCE-DREO increased gradually with increasing concentration of PEI. The leaching efficiency of rare earths was increased from 93.94% to 95.24% by the compound leaching agent consisting of 0.4% PEI and 2% ammonium sulfate compared to 2% ammonium sulfate alone, and the leaching time was reduced by about 33%. PEI can produce a large amount of —NH₃⁺ by hydrolysis, which can neutralize the negative charge on the interlamination and surfaces of clay minerals, reduce the electrostatic repulsion, and weaken the hydration and swelling of clay minerals. A polymeric film was formed on the clay particles by PEI coating, which changed the hydrophilicity of the particle surface, reduced water intrusion. Small particles were agglomerated by the wrapping and linking effects of long-chain PEI, thus increasing the particle size and facilitating the percolation of leaching agent. PEI skeleton also could embed in the clay interlayer and extrude the interlayer water, which inhibits the swelling of clay minerals.