Phase Chemistry Study of the Zabuye Salt Lake Brine: Isothermal Evaporation at 15°C and 25°C

Zabuye Salt Lake in Tibet, China is a carbonate-type salt lake, which has some unique characteristics that make it different from other types of salt lakes. The lake is at the latter period in its evolution and contains liquid and solid resources. Its brine is rich in Li, B, K and other useful minor elements that are of great economic value. We studied the concentration behavior of these elements and the crystallization paths of salts during isothermal evaporation of brine at 15 degrees C and 25 degrees C. The crystallization sequence of the primary salts from the brine at 25 degrees C is halite (NaCl) -> aphthitalite (3K(2)SO(4)center dot Na2SO4) -> zabuyelite (Li2CO3) -> trona (Na2CO3 center dot NaHCO3 center dot 2H(2)O) -> thermonatrite (Na2CO3 center dot H2O) center dot sylvite (KCl), while the sequence is halite (NaCl) -> sylvite (KCl) -> trona (Na2CO3 center dot NaHCO3 center dot 2H(2)O) -> zabuyelite (Li2CO3) -> thermonatrite (Na2CO3 center dot H2O) -> aphthitalite (3K(2)SO(4)center dot Na2SO4) at 15 degrees C. They are in accordance with the metastable phase diagram of the Na+, K+-Cl-, CO(3)2-, SO42--H2O quinary system at 25 degrees C, except for Na2CO3 center dot 7H(2)O which is replaced by trona and thermonatrite. In the 25 degrees C experiment, zabuyelite (Li2CO3) was precipitated in the early stage because Li2CO3 is supersaturated in the brine at 25 degrees C, in contrast with that at 15 degrees C, it precipitated in the later stage. Potash was precipitated in the middle and late stages in both experiments, while boron was concentrated in the early and middle stages and precipitated in the late stage.