Predominance diagrams of dissolved uranium species and logfO_2(g)-pH diagrams of U-PO_4~(3-)-NaCI-H_2O system at 25°C , PCO_2=10~(-3.5) MPa

摘要

To explore the effect of logfO_2(g), pH, uranium concentration, phosphate concentration and NaCl concentration on the predominance diagrams of dissolved uranium species and formation of solid phases containing uranium in the U-PO_4~(3-)-NaCl-H_2O system at 25°C and PCO_2=10~(-3.5) MPa, the thermodynamic model of this system was constructed. Based on the results of calculation, the logfO_2(g)-pH diagrams were drawn. It can be found that: 1) the formation of uraninite needed enough reductive condition (about logfO_2(g) < -50 ), while the formation of Na-Autunite needed the strict pH range(5H<8) in oxidative condition. 2)The addition of phosphate concentration could promote the formation of Na-Autunite, and inhibit the formation of U_4O_9(C). 3)The independent increasing of uranium concentration can lead to more kinds of uranium species.4) The variance of NaCl concentration had little impact on the formation of solid phases containing uranium.