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Computer Coupling of Phase Diagrams and Thermochemistry 27 (2003) 343–352 www.elsevier.com/locate/calphad

Thermodynamics and phase diagram of the salt lake brine system at 298.15 K V. Model for the system Li+ , Na+, K+, Mg2+/Cl− , SO2− –H2 O and its 4 applications
Pengsheng Song∗, Yan Yao
Qinghai Institute of Salt Lakes, The Chinese Academy ofSciences, Xi’ning, Qinghai Province, 810008, China Received 20 June 2003; accepted 2 February 2004

Abstract As one of a series of papers related to thermodynamics and phase equilibrium for the “Salt Lake Brine System”, the present paper deals with the system Li+ , Na+ , K+ , Mg2+ /Cl− , SO2− –H2 O. In order to describe thermodynamics and phase equilibrium of the title system, the 4 Pitzer ioninteraction model of aqueous electrolyte was applied. In addition to Pitzer parameters for single electrolytes for the entire range of concentration up to the saturation, the mixing parameters for pairwise ions including ion Li+ , such as (Li+ , Na+ ), (Li+ , K+ ), (Li+ , Mg2+ ), and for triple ions (Li+ , Na+ , Cl− ), (Li+ , Na+ , SO2− ), . . . and (Cl− , SO2− , Li+ ) etc are also needed. We managedto obtain reasonable 4 4 Pitzer parameters for single electrolytes and the osmotic coefficient of LiCl–NaCl–H2 O solutions were determined in our lab. All our data together with those published were fitted to acquire the needed parameters. The model has been extended to the system including ion Ca2+ in our recent work. The parameterized model of Pitzer has been applied in many aspects in our work.The calculation of thermodynamic properties of brines, prediction of solubilities for the title system and its subsystems with Li-salts, and predicting the sequences of salt precipitation during the evaporation of brines at 298.15 K etc are presented in the paper. © 2004 Published by Elsevier Ltd

1. Introduction Brines of salt lakes on the Qinghai-Xizang Plateau are characterized by a highconcentration of lithium and boron. The other constituents are similar to the sea water system Na+ , K+ , Mg2+ /Cl− , SO2− –H2 O. In order to describe 4 thermodynamics and phase equilibrium of the salt lake brine system by using the Pitzer model, the mixing parameters with the ion Li+ for the Li+ , Na+ , K+ , Mg2+ /Cl− , SO2− –H2 O system are all needed. 4 According to the Pitzer model of aqueouselectrolytes the mixing parameters are divided into two types: θ(i, j ) , the parameter of two ions with the same sign, and ψ(i, j,k) , the parameter of two ions with the same sign and an ion with

the opposite sign. And the mixing parameters do not depend on the order of ions, that is: θ(i, j ) = θ( j,i) ; ψ(i, j,k) = ψ( j,i,k)

where i , j denote two definite ions with the same sign. As to thesalt lake brine system, the following mixing (0) parameters are needed in addition to the parameters β M X , φ (1) (2) β M X , β M X and C M X for pure electrolyte LiCl and Li2 SO4 : θLi,Na , ψLi,Na,Cl , ψLi,Na,SO4 , θLi,K , ψLi,K,Cl , ψLi,K,SO4 θLi,Mg, ψLi,Mg,Cl , and ψCl,SO4 ,Li . ψLi,Mg,SO4 ,

∗ Corresponding author. Tel.: +86-971-630-5173; fax: +86-971-6306002. E-mail address:songpsh@isl.ac.cn (P. Song).

We also need the standard Gibbs energy of formation for Li-salts when the method of the minimization of the total Gibbs energy of the system is used to compute the equilibrium composition. All parameters for the system Li+ , K+ , Mg2+ /Cl− , SO2− –H2 O and the standard Gibbs 4 energy of formation for LiCl·MgCl2 ·7H2 O, LiCl·H2 O,

0364-5916/$ - see front matter © 2004 Publishedby Elsevier Ltd doi:10.1016/j.calphad.2004.02.001

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P. Song, Y. Yao / Computer Coupling of Phase Diagrams and Thermochemistry 27 (2003) 343–352

Table 1 Parameters and data sources of the fit System and needed parameters Li, Mg/Cl, SO4 –H2 O Seven parameters: θLi,Mg , ΨLi,Mg,Cl , ΨLi,Mg,SO4 , µ0 /RT i of LiCl·H2 O, LiCl·MgCl2 ·7H2 O and Li2 SO4 ·H2 O σ = 0.049 Li, K/Cl, SO4 –H2 O Six...