USE OF GEOCHEM-PC TO PREDICT RARE-EARTH ELEMENT (REE) SPECIES IN NUTRIENT SOLUTIONS

The interpretation of results of some experiments examining effects of rare earth elements (REE) on plant growth may have been complicated b y rare earth phosphate precipitation. Simulations were undertaken usin g the computer model GEOCHEM-PC to define REE solubility limits and pr edict REE species in low and high ionic strength nutrient solutions. I n low ionic strength solutions containing 5 mu M P, lanthanum phosphat e (LaPO4) precipitation is predicted to occur at solution pH>4.0, reac hing a maximum (>95% of total) at pH 5.5. In high ionic strength solut ions (1000 mu M P) over 95% of the La is predicted to precipitate as p hosphate at pH>4.0. The predicted behaviour of cerium (Ce) was closely similar to that for La. At pH 5.5, the concentration of REE species i n solution can be increased only after virtually all the P has been pr ecipitated. Consequently, it is important to consider REE-P interactio ns in nutrient solutions when investigating REE effects on plant growt h.