Article pubs.acs.org/jced
Mean Activity Coefficients of KBr in the KBr−K2SO4−H2O Ternary System at 298.15 K by an Electromotive Force Method Jun-Jie Zhang,†,‡ Shi-Hua Sang,*,†,‡ and Si-Yao Zhong†,‡ †
College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, ChengDu 610059, P. R. China Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, ChengDu 610059, P. R. China
‡
ABSTRACT: The mean activity coefficients of KBr in the KBr−K2SO4−H2O ternary system were determined at the total ionic strength ranging from (0.0100 to 3.0000) mol·kg−1 at 298.15 K by the electromotive force (EMF) method from the battery cell without a liquid junction: K-ISE|KBr(m1), K2SO4(m2)|Br-ISE. The mean activity coefficients of KBr were compared with those different ionic strength fractions yB of K2SO4 with yB = (0.8, 0.6, 0.4, 0.2, and 0). The experimental results showed that K-ISE and Br-ISE in this work had a good Nernst response, and the mean activity coefficients of KBr were fitted to the Pitzer models. Pitzer ion interaction parameters of θBr−·SO42− and φK+·Br−·SO42− which had not been reported were evaluated from present measurements of the mean activity coefficients of KBr.
1. INTRODUCTION Electrolyte solution exists widely in nature. Because it is been applied to seawater desalination, brine development, wet metallurgy, and earth science, many researchers have made great efforts to contribute thermodynamic data to the scientific literature.1−4 Activity coefficients are an important thermodynamics property of mixed electrolytes solution.5−8 There are conductance method, freezing point drop method, isopiestic method, and electromotive force (EMF) techniques to determine the activity coefficient.9 In recent years, these have evolved into a simple and practical method with an ion selective electrode measuring activity coefficients of mixed electrolyte solution components. The ion selective electrode has a wide range of linear response, high sensitivity, good selectivity, and analysis speed, and it is easy to realize automatic and continuous measurement and control, so it catches people’s attention.10−12 Electrolyte solution has abundant resources about underground brines in Western Sichuan basin.13 Sodium chloride, potassium, boron, bromine, and sulfates are the major chemical components of oilfield brine, which often accompanies Li, Sr, and I. The content of all can reach or exceed industrial grade, with high economic value for exploitation.14,15 The exploitation of underground brine resources, rich in potassium, can make up for the shortage of potassium resources. As a result, thermodynamic properties for the composition of the brines are important basic data. Thermodynamic properties play an important role in exploiting and utilizing the underground brines. Therefore, it is necessary for us to scientifically exploit these natural resources in a preliminary investigation of salt brine chemistry. The ternary system KBr−K2SO4− H2O is a subsystem of the brines. So far, no report has been found on the thermodynamic properties of this ternary system at 298.15 K. In the early stage © 2012 American Chemical Society
we studied the phase diagram for a series of subsystems under the Na+,K+//Cl−,Br−,SO42−,B4O72−−H2O system.16,17 To predict the phase diagram of the underground brine using electrolyte solution models, we carried out to determine the thermodynamic properties experimentally. In this paper, the activity coefficients of KBr in KBr and K2SO4 mixed aqueous solution were determined by EMF measurements at 298.15 K and in the (0.0100 to 3.0000) mol·kg−1 total ionic strength range, and the Pitzer’s ion interaction parameters of θBr−·SO42− and φK+·Br−·SO42− were evaluated by using the activity coefficients of KBr in KBr and K2SO4 mixed aqueous solution.
2. EXPERIMENTAL SECTION The chemical reagents are deionized water through a second reverse osmosis process, at a conductivity
