Concentrations of rare earth elements in some Australian soils

Total, exchangeable, and soil solution concentrations were measured for 15 rare earth elements (REEs) in 9 soils from Queensland and New South Wales. In a further 10 acid soils, effects of amendment with CaCO or CaSO·2HO were measured on the concentrations of REEs in soil solution. The total concentration of the REEs in soil solutions from unamended soils ranged from below the detection limit (0.007 μM) to 0.64 μM. Lanthanum (La) and cerium (Ce) were the REEs present in the greatest concentrations, the highest concentrations measured in the diverse suite of soils being 0.13 μM La and 0.51 μM Ce. Rare earth elements with higher atomic numbers were present in very low concentrations. Exchangeable REEs accounted for 0.07 to 12.6% of the total REEs measured in the soils. Addition of CaCO increased soil solution pH and decreased REE concentrations in soil solution, whilst CaSO·2HO decreased soil solution pH and increased the concentrations of REEs in soil solution. Solubility calculations suggest that CePO may be the phase controlling the concentration of Ce in soil solution