Abstract:

The brine of Jilantai Salt Lake is aging gradually with the exploitation of salt lake resources for a long time,which leads to the decline of recycled salt quality year by year. In order to solve the problems such as brine aging and SO₄ ^2- enrichment,aiming at the Na ⁺,Mg ²⁺∥Cl ^-,SO₄ ^2--H₂O system in Jilantai Salt Lake,the salt crystallization law of frozen mirabilite of dredging area brine and frozen mirabilite mother liquor evaporation was studied by constant temperature freezing method and forced evaporation constant temperature equilibrium method.The effect of freezing mirabilite temperature,water addition rate and frozen mirabilite time on denitrification rate and SO₄ ^2- removal rate were investigated.And the evaporation rate on the salt crystallization of evaporation was also studied.The optimum condition of freezing mirabilite was as follows：the brine addition rate was 8%（mass fraction）,the brine density decreased to 1.197 8 g/cm ³,freeze for 12 h under -10 ℃,then the brine density was low to 1.186 6 g/cm ³,the mass concentration of SO₄ ^2- in brine decreased to 8.84 g/L and the precipitation rate of mirabilite was 73.76%. After the frozen mirabilite,the brine was evaporated until density of the brine reaching 1.260 1 g/cm ³ under 25 ℃.The precipitation rate and purity of sodium chloride were 93.14% and 96.23%,respectively.This study provides a theoretical basis for the optimization of brine production of high grade recycled salt in ship mining area.

Key words: Jilantai Salt Lake, frozen crystallization law of mirabilite, phase diagram, evaporation-crystallization law