Measurements And Calculations Of Solid-Liquid Equilibria In The Quinary Systems Focused On Underground Brine Enriched In Bromine And Strontium At Multi-temperature

According to the composition of the brine resources in the Sichuan Basin,phase equilibria in the quinary systems NaBr–KBr–Na₂SO₄–K₂SO₄–Na₂B₄O₇–K₂B₄O₇–H₂O at 298 K,NaBr–KBr–MgBr₂–CaBr₂–H₂O at（298 and 323）K,NaBr–KBr–MgBr₂–SrBr₂–H₂O at 323 K,quaternary system NaBr–KBr–Na₂SO₄–K₂SO₄–H₂O and their relevant subsystems were studied by the method of isothermal solution saturation method.The compositions of liquids in these systems were determined experimentally.Using the experimental data,the phase diagrams of listed above systems were obtained.The solubilities for the subsystems were calculated by Pitzer’s equation.The experimental results show that the phase diagrams of ternary systems NaBr–SrBr₂–H₂O and KBr–SrBr₂–H₂O at（298,323,348）K,NaBr–Na₂SO₄–H₂O and KBr–K₂SO₄–H₂O at 348 K are all type of simple common-saturation,and without complex salt and solid solution.It can be found that there are all in one eutectic point,two univariant curves and two regions of crystallization.There is double salt Na₂SO₄·3K₂SO₄ in the phase diagrams of quaternary system NaBr–KBr–Na₂SO₄–K₂SO₄–H₂O at（298 and 348）K.Compared with the quaternary phase diagram at two temperatures,the crystallization field of NaSO₄·10H₂O was not found at 348 K.The phase diagrams of quaternary systems KBr–K₂SO₄–K₂B₄O₇–H₂O,NaBr–Na₂SO₄–Na₂B₄O₇–H₂O,NaBr–KBr–Na₂B₄O₇–K₂B₄O₇–H₂O at 298 K,NaBr–KBr–SrBr₂–H₂O,NaBr–KBr–Ca Br₂–H₂O at（298 and 323）K and NaBr–MgBr₂–SrBr₂–H₂O at 323 K all belong to the simple type.The double salt（Na₂SO₄·3K₂SO₄）were found in the quaternary systems NaBr–KBr–MgBr₂–H₂O,KBr–CaBr₂–MgBr₂–H₂O at（298 and 323）K and KBr–MgBr₂–SrBr₂–H₂O at 323 K.In addition to this double salt,there is another double salt 2MgBr₂·CaBr₂·12H₂O in the quaternary systemKBr–CaBr₂–MgBr₂–H₂O at 323 K.The double salt aphthitalite（Na₂SO₄·3K₂SO₄）was found in the quinary system NaBr–KBr–Na₂SO₄–K₂SO₄–Na₂B₄O₇–K₂B₄O₇–H₂O at 298 K.In the phase diagram（saturated with Na₂B₄O₇）,there are eleven univariant curves,five invariant points and seven crystallization regions saturated with Na₂B₄O₇·10H₂O,where the solids are Na₂SO₄,K₂SO₄,Na₂SO₄·3K₂SO₄（Gla）,Na₂SO₄·10H₂O,NaBr·2H₂O,KBr and K₂B₄O₇·4H₂O.The phase diagram of quinary system NaBr–KBr–MgBr₂–CaBr₂–H₂O at 298 K contains five univariant curves,two invariant points and four crystallization fields（saturated with KBr）: Na Br·2H₂O,NaBr,KBr,KBr·MgBr₂·6H₂O and CaBr₂·6H₂O.In addition to the complex salt KBr·MgBr₂·6H₂O,the complex salt 2MgBr₂·CaBr₂·12H₂O also crystallizes from the saturated solutions at 323 K.There are three invariant points,seven uninvariant curves,and five crystallization fields at 323 K.Respectively,the corresponding balance solid phase are NaBr·2H₂O,NaBr,KBr,KBr·MgBr₂·6H₂O,CaBr₂·4H₂O and 2MgBr₂·CaBr₂·12H₂O.The results show that there is double salt KBr·MgBr₂·6H₂O formed in the quinary system NaBr–KBr–MgBr₂–SrBr₂–H₂O at 323 K.The phase diagram of this system consists of three invariant points,ten univariant curves and six crystallization fields: NaBr·2H₂O,Na Br,MgBr₂·6H₂O,SrBr₂·6H₂O,KBr·MgBr₂·6H₂O and KBr.Using the experimental solubilities data of ternary subsystems,the non-reported parameters were acquired by the multiple linear regression method.The patameters include ΨNa,SO₄,B₄O5（OH）4,ΨK,SO₄,B₄O5（OH）4,θBr,B₄O5（OH）4,ΨNa,Br,B₄O5（OH）4,ΨK,Br,B₄O5（OH）4,θMg,Sr,ΨNa,Sr,Br,ΨK,Sr,Br,ΨMg,Sr,Br,ΨMg,Sr,Cl at 298 K and ΨNa,Br,SO₄,ΨK,Br,SO₄ at 348 K.Based on the chemical model of Pitzer’s electrolyte solution theory,the solubilities of phase equilibria in systems were calculated using PSO algorithm.It included four ternary systems（NaBr–SrBr₂–H₂O,KBr–SrBr₂–H₂O,MgBr₂–SrBr₂–H₂O,MgCl2–SrCl2–H₂O）,seven simple quaternary systems NaBr–KBr–SrBr₂–H₂O,NaBr–MgBr₂–SrBr₂–H₂O,KBr–MgBr₂–SrBr₂–H₂O,NaCl–MgCl2–SrCl2–H₂O,KCl–MgCl2–SrCl2–H₂O,NaBr–Na₂SO₄–Na₂B₄O₇–H₂O,KBr–K₂SO₄–K₂B₄O₇–H₂O at 298 K,three simple quaternary systems NaBr–KBr–MgBr₂–H₂O,NaBr–KBr–CaBr₂–H₂O,KBr–MgBr₂–CaBr₂–H₂O at（298 and 323）K,and one interaction quaternary system NaBr–KBr–Na₂SO₄–K₂SO₄–H₂O at（298 and 348）K.Compared experimental measurement with calculation,the results showed that the calculated diagrams are basically in agreement with experimental diagrams.The deviation and errors were also analyzed.