Leaching kinetics and permeability of polyethyleneimine added ammonium sulfate on weathered crust elution-deposited rare earth ores

At present, in-situ leaching of weathered crust elution-deposited rare earth ores (WCE-DREO) encounter with problems such as long leaching cycles, slow infiltration rate and low product purity. In order to solve the above problems, the conventional leaching agent ammonium sulfate ((NH4)2SO4) was compounded with polymeric surfactant polyethyleneimine (PEI) to form a composite leaching agent. The effects of leaching temperature, PEI concentration, flow rate and pH on leaching kinetics and permeability of rare earths (RE) and aluminum (Al) in orebody were studied. The following results were concluded: with temperature increase, the time required to reach leaching equilibrium for both RE and Al were shortened, the apparent activation energies of RE and Al were 14.79 kJ/mol and 13.45 kJ/mol, respectively, and the leaching processes were in accordance with the outer diffusion control. When the concentrations of (NH4)2SO4 and PEI in the composite leaching agent were 2.0 wt% and 0.4 wt%, the time required to reach leaching equilibrium for RE and Al was about 50% shorter than using (NH4)2SO4 alone, and the leaching efficiencies of RE were slightly higher than that of Al. Properly increasing the temperature and flow rate of the composite leaching agent could improve the leaching efficiencies of RE and Al, but pH had neglected effects on the leaching efficiencies of RE. At PEI concentrations below 0.4 wt%, the addition of PEI promoted the leaching of RE and Al. In column leaching studies of the WCE-DREO, the addition of 0.4 wt% PEI to the traditional leaching agent (NH4)2SO4) had no impact on the leaching efficiencies of RE. However, it could significantly increase the infiltration rate of WCE-DREO, shortening the leaching time per 10 mL effluent from about 30 min for (NH4)2SO4 leaching system to 20 min for the composite leaching system. The leaching time was shortened by one-third, and the leaching costs was reduced, which could provide theoretical guidance for the development and commercial implementation of novel composite leaching agent for WCE-DREO.