hydrothermal properties of materials experimental data on aqueous phase equilibria and solution properties at elevated temperatures and pressures

Vladimir Mikhailovich Hydrothermal properties of materials : experimental data on aqueous phase equilibria and solution properties at elevated temperatures and pressures / Vladimir Val

Hydrothermal Experimental Data Edited by V.M Valyashko

© 2008 John Wiley & Sons, Ltd ISBN: 978-0-470-09465-5

Edited by Vladimir M Valyashko

A John Wiley & Sons, Ltd., Publication

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Library of Congress Cataloging-in-Publication Data

Valyashko, V M (Vladimir Mikhailovich)

Hydrothermal properties of materials : experimental data on aqueous phase equilibria and solution properties at elevated

temperatures and pressures / Vladimir Valyashko.

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 978-0-470-09465-5

Typeset in 10/12 pt Times New Roman PS by SNP Best-set Typesetter Ltd., Hong Kong

Printed and bound in Singapore by Markono Print Media Pte Ltd, Singapore

This book is dedicated to the memory of Professor Dr E U Franck (Ulrich Franck) (1920–2004) who made fundamental contributions in the fi eld of solution chemistry and phase equilibria in aqueous systems at high temperatures and pressures,

and whose idea to create an ‘Atlas on Hydrothermal Chemistry’ was realised with the publication of Aqueous Systems at

Elevated Temperatures and Pressures in 2004 and this book.

1.2 Experimental methods for studying hydrothermal phase equilibria 3

1.3.3 Graphical representation and experimental examples of binary phase diagrams 91

1.4.1 Graphical representation of ternary phase diagrams 1031.4.2 Derivation and classifi cation of ternary phase diagrams 105

2 pVTx Properties of Hydrothermal Systems 135

Horacio R Corti and Ilmutdin M Abdulagatov

3 High Temperature Potentiometry 195

Donald A Palmer and Serguei N Lvov

3.1.3 Diffusion, thermal diffusion, thermoelectric, and streaming potentials 199

4.3.1 Static high temperature and pressure conductivity cells 215

4.5.1 Specifi c conductivity as a function of temperature, concentration and density 221

4.5.3 Concentration dependence of the molar conductivity and association constants 2234.5.4 Molar conductivity as a function of temperature and density 224

7 Calorimetric Properties of Hydrothermal Solutions 271

Vladimir M Valyashko and Miroslav S Gruszkiewicz

Appendix to Chapter 1 pTX

Appendix to Chapter 2 pVTX

Appendix to Chapter 3 Potentiometry

Appendix to Chapter 4 Electrical Conductivity

Appendix to Chapter 5 Thermal Conductivity

Appendix to Chapter 6 Viscosity

Appendix to Chapter 7 Calorimetric

Dr Vladimir Valyashko invited me to write the foreword

to this substantial book that contains all existing evaluated

experimental data on thermodynamic, electrochemical, and

transport properties of two- and three-component aqueous

systems in the hydrothermal region This invitation is

unquestionably quite an honor However, accepting it did

make me feel somewhat of an impostor The person who

should have written this foreword is our revered

predeces-sor, colleague and friend Ulrich Franck, but unfortunately,

he did not live to see the completion of an endeavor that he

had most arduously advocated It is therefore with

trepida-tion that I, who consider myself at best as one of his many

disciples, act here as his substitute

An immense amount of experimental material on water/

steam and aqueous systems has been obtained during the

past century, and even before, in laboratories around the

world, much of it not readily accessible Especially during

the cold-war years, the International Association for

Proper-ties of Water and Steam (IAPS, later IAPWS) was among

the few international organizations in which experts in the

former Soviet Union actively participated Franck, impressed

by the access IAPWS had to experimental data obtained

worldwide, repeatedly urged the organization to collect and

evaluate these data, bundling them in what he used to call

an Atlas

This book presents evaluated experimental data acquired,

as well as some of the theoretical models developed, for

two-and three-component hydrothermal systems These are

aqueous solutions containing both molecular and/or

electro-lytic solutes at high temperature and pressure, approaching

and exceeding water’s critical temperature Hydrothermal

systems are ubiquitous, in the deep ocean and in the earth’s

crust, and of major importance in geology, geochemistry,

mining, and in industrial practices such as metallurgy and

the synthesis and growth of crystals

The theoretical understanding of the phase behavior of

fl uid mixtures was developed in the second half of the 19th

century, starting with the work of Gibbs (1873–1878) and

culminating in Van der Waals’s theory of mixtures (1890),

which was a generalization of his 1873 equation of state

The fi rst phase separation experiments by Kuenen (early

1890s) involved binary mixtures of simple organics both

below and above the critical point of the more volatile

component Gradually, between the early 1890s and 1903,

the various types of binary fl uid phase separation became

known Van Laar actually was able to derive them from a

version of Van der Waals’s mixture equation Nature’s most

unusual fl uid: “associating” water, however, with its very

high critical point, and its high dielectric constant yielding

electrolytic properties in the liquid phase, was not expected

to behave as air constituents and organics

The question of how the solvent water would behave around and above its critical point was fi rst addressed by the Dutch chemist Bakhuis Roozeboom and his school, who were experts at measuring and classifying the phase separa-tion of binary and ternary mixtures, including solid phases

By 1904, Bakhuis Roozeboom had explored the case of the liquid-vapor-solid curve intersecting the critical line of a binary mixture in two critical endpoints and predicted that this would also happen in aqueous solutions of poorly soluble salts, as his successors indeed confi rmed in 1910 His experiments and classifi cation scheme pertain to a mul-titude of both non-aqueous and aqueous binary and ternary systems

Somewhat fortuitously, Göttingen became the nexus from which “phase theory” would spread to Russia The Russian organic chemist Vittorf (1869–1929) met Bakhuis Roozeboom in Göttingen in 1904 Vittorf then used Bakhuis Roozeboom’s phase theory and classifi cation as the basis for his own 1909 book “Theory of Alloys in Application to Metallic Systems” From the late 1930s through the 1980s, physical chemist Krichevskii and his many collaborators, thoroughly familiar with the work of the Dutch School, studied fl uid phase behavior and critical phenomena experi-mentally, and discovered several predicted effects, such as tricriticality, as well as gas-gas phase separation in both nonaqueous and aqueous mixtures Starting just after WWII, thermal physicist Stirikovich, physical chemists Mashovetz and Ravich, and geochemist Khitarov, began to explore phase behavior and solution properties of aqueous systems

up to high temperatures and pressures

Göttingen professors Nernst, Tammann, and Eucken had built a physical chemistry laboratory for electrochemistry,

as well as for high-pressure phase equilibria studies and calorimetry It was there that Franck, a pupil of Eucken, began his life’s work on the experimental exploration of the properties of high-temperature, high-pressure aqueous solu-tions of air constituents, acids, bases, and salts, studying phase behavior as well as dielectric and electrochemical properties He and his disciples explored this fi eld through-out the second half of the 20th

century

In the USA, just after WWI, geochemist Morey began the fi rst phase equilibria studies in hydrothermal systems

By the middle of the 20th

century, there was a fl ourishing discipline in geochemistry in the USA, culminating the work of Kennedy and collaborators on phase separation

in aqueous salt solutions at high pressures and tures Time and again, it was rediscovered that the phase

tempera-separation characteristics of fl uid mixtures fi rst classifi ed by

Bakhuis Roozeboom do apply to aqueous systems as well

Valyashko, the chief editor of the present book, has,

throughout the years, exhaustively classifi ed the

experimen-tal phase diagrams of binary and ternary aqueous solutions

including solid phases in the hydrothermal range He

fre-quently consulted with Franck, and assembled the work in

collaboration with Lentz, from the Franck school This

work forms a substantial part of the present book

Independently, however, in the 20th

century, physical chemists studying aqueous electrolyte solutions set up a

framework of description unlike that used for fl uid

mix-tures It is founded on increasingly more detailed and

accu-rate measurement and modeling of electrolyte solution

properties in the solvent water, usually below the boiling

temperature Here the pure solvent at the same pressure and

temperature, and the infi nite-dilution properties of the

solute, serve as an asymmetric reference state Kenneth

Pitzer was a pioneer in this fi eld, systematically pushing the

modeling of solution behavior to higher concentrations and

temperatures Geochemist Helgeson and his school

intro-duced practical models for use in the fi eld

On approaching the critical point, however, water’s

unusual dielectric and electrolytic properties diminish, its

compressibility increases hugely, and its behavior becomes

more like that of other, simpler near-critical fl uids The

asymmetric solution model then becomes increasingly

strained This message was brought home forcefully in the

early 1980s by the elegant experimental data of Wood and

coworkers on partial molar properties of the solute in dilute

electrolyte solutions near the water critical point These

usually well-behaved properties exhibited divergences at

that critical point, while higher derivatives, such as the

partial molar heat capacity, displayed wild swings in water’s

critical region When Wood et al repeated the experiments

in the argon-water system, however, similar anomalies were

found, be it of the opposite sign and of smaller amplitude – a

sure sign that the effects they had seen were not electrolytic

in origin, but a general thermodynamic property of a dilute near-critical mixture In fact, in the early 1970s, Krichevskii and coworkers had discovered the divergence of the infi nite-dilution partial molar volume of the solute experi-mentally, and explained it correctly

Aqueous mixtures near and above the water critical point can then be modeled by Van der Waals-like descriptions of

fl uid mixtures that treat the solvent and solutes equivalently but ignore the charges Franck and coworkers, for instance, produced the phase separations observed in several binary and ternary aqueous systems in the hydrothermal range from simple Van-der-Waals type models

A theory that combines in a unifi ed way the electrolytic behavior with Van-der Waals-like classical critical behavior (let alone the actual non-classical critical behavior known

to characterize water as well as all other fl uids) remains a formidable challenge Recent fundamental work by M.E Fisher and coworkers is making this increasingly clear.The various chapters of the present book, instead, offer

a practical and useful overview of modeling approaches, focused on the current needs, methods and understanding

of a wide range of hydrothermal systems They show a discipline still in development, one of the last enduring challenges in the fi eld of thermodynamics and electrochem-istry of solutions The book may transcend Franck’s original concept of an “Atlas,” but he certainly would have been most pleased with the authors’ efforts of understanding and representing data, an effort that he himself amply exempli-

fi ed in his scientifi c output of half a century It is my hope and expectation that the book will be received by a diverse class of users as a highly useful compendium of knowledge about hydrothermal systems, accumulated globally over more than a century

Johanna (Anneke) Levelt Sengers

Scientist Emeritus National Institute of Standards and Technology

Gaithersburg, MD, USA

Knowledge of equilibria in aqueous systems as well as

understanding the processes occurring in hydrothermal

mixtures are based to a large extent on experimental data

on phase equilibria and solution properties for aqueous

systems at temperatures above 150–200 °C These data have

been extensively applied in a variety of fi elds of science and

technology, ranging from development of the chemistry of

solutions and heterogeneous mixtures, thermophysics,

crys-tallography, geochemistry and oceanography to industrial

and environmental applications, such as electric power

gen-eration, hydrothermal technologies of crystal growth and

nanoparticle syntheses, hydrometallurgy and the treatment

of sewage and the destruction of hazardous waste

The available experimental data for binary and ternary

systems can be used as primary reference data, or as the

initial values for further refi nement, in order to obtain

rec-ommended values, particularly, the internally consistent

values that are used for thermodynamic calculations and

modelling of multicomponent equilibria and reactions

However, the recommended values are derivatives and

largely depend on the method of treatment based on more

or less rigorous and varying models Thus, a collection of

experimental data not only incorporates original

informa-tion from widely scattered scientifi c publicainforma-tions, it is

fun-damental and provides the foundation for modern and future

databases, and recommended values

The main goals of this book are to collect, collate and

compile the available original experimental data on phase

equilibria and solution properties for binary and ternary

hydrothermal systems, to review these data, and to consider

the employed experimental methods and the ways these data

were refi ned/processed and presented

The work on collecting hydrothermal experimental data

was started in the mid-1990s by Dr V M Valyashko

(Kur-nakov Institute of General and Inorganic Chemistry, Russian

Academy of Sciences (KIGIC RAS), Moscow, Russia) and

Dr H Lentz (University of Siegen, Germany) and was

sup-ported by the Russian Fund for Basic Research and the

Deutsche Forschungsgemeinschaft After the retirement of

Dr Lentz in 1999, collection of data at temperatures above

200 °C was continued by Dr Valyashko and Mrs Ivanova

(KIGIC RAS)

The development of the project was supported by the

International Association for the Properties of Water and

Steam (IAPWS), the organization which is renowned for

setting international standards for properties of pure water

and high-temperature aqueous systems

According to the IAPWS project accepted in 2004, this

book should have had seven chapters – Phase equilibria

data, pVTX data, Calorimetric data, Electrochemical data, Electrical conductivity data, Thermal conductivity data and Viscosity data However, the planned chapter on calorimetry was not forthcoming due to personal commitments of the author Only a summary table of calorimetric data with a short introduction about the experimental methods used for hydrothermal measurements are provided in Chapter 7 of this book but a collection of the experimental calorimetric data is available on the CD

In the fi nal version of this book each chapter consists of two parts: the descriptive text part that appears in the pages

of this book and the data part which appears as appendices organized on the CD The descriptive part contains the basic principles and defi nitions, description of experimental methods, discussion of available data and reviews of theo-retical or empirical approaches used for treatment of the original experimental values The accompanying summary tables, arranged in alphabetic order of the nonaqueous com-ponents, list the temperatures, pressures and concentrations, types of data and experimental methods employed in their measurements, the uncertainty claimed by the authors as well as the references (the fi rst author and the year of pub-lication) The table code refers the reader to the original data set in the appendices on the CD The tables of experimental data (with brief comments on each set of experimental measurements) in the appendices are also arranged in alpha-betic order of nonaqueous components However, the order

of the systems in the appendices is usually not exactly the same as in the summary tables There are no subdivisions

in appendices, whereas in the summary tables the binary and ternary systems are often placed in separate divisions

or subdivisions such as inorganic and organic compounds

or electrolytes, nonelectrolytes, acids, etc

The text parts of the chapters, besides the general acteristics of the available experimental data mentioned above, usually contain several special topics and aspects of material presentation

char-Chapter 1 (Phase Equilibria in Binary and Ternary thermal Systems, V M Valyashko, Russia) contains a description of the general trends of sub- and supercritical phase behaviour in binary and ternary systems taking into account both stable and metastable equilibria A presenta-tion of the various types of phase diagrams aims to show the possible versions of phase transitions under hydrother-mal conditions and to help the reader with the determination

Hydro-of where the phase equilibrium occurs in p–T–X space, and what happens to this equilibrium if the parameters of state are changed Special attention is paid to continuous phase transformations taking place with variations of temperature,

pressure and composition of the mixtures, and to a

system-atic classifi cation and theoretical derivation of binary and

ternary phase diagrams

Chapter 2 (pVTx Properties of Hydrothermal Systems,

H R Corti (Argentina) and I M Abdulagatov (Russia/

USA)) describes many theories and models developed to

accurately reproduce the excess volumetric properties and

to assess the standard partial molar volumes of the solute in

aqueous electrolyte and nonelectrolyte solutions under sub-

and supercritical conditions Most of these models and

equations, particularly the equations of state, are used to

compute both the thermodynamic properties of solutions

and the phase equilibria This chapter is concerned with

theoretical approaches in modern chemical

thermodynam-ics of hydrothermal systems

Chapter 3 (High Temperature Potentiometry, D A Palmer

and S N Lvov (USA)) focuses on ionization equilibria that

are an important part of acid–base, metal–ion hydrolysis,

metal complexation and metal–oxide solubility studies

under hydrothermal conditions Most of the hydrothermal

investigations used potentiometric measurements with

various types of electrochemical cells, mainly covering

ranges of temperature below 200 °C, the minimum limit

generally adhered to in this book Therefore, the

experimen-tal data discussed in the text part, collected in the appendix

and in the summary tables include both high-temperature

(up to 400–450 °C) and low-temperature results available in

the literature

Special attention in Chapter 4 (Electrical Conductivity in Hydrothermal Binary and Ternary Systems, H R Corti (Argentina)) is paid to the procedures for obtaining infor-mation on the thermodynamic properties of electrolytes (including a determination of the limiting conductivity and association constants) from the measured electrical conduc-tivity of diluted solutions above 200 °C However, the behaviour of specifi c and molar conductivity in concen-trated electrolyte solutions is also carefully discussed in the chapter

Chapters 5 and 6 (Thermal Conductivity and Viscosity,

I M Abdulagatov (Russia/USA) and M J Assael (Greece)) show not only the typical temperature, pressure and con-centration dependencies of properties in hydrothermal solutions, but also make a preliminary comparison of various datasets for several systems to help the reader choose which values to use The empirical and semi-empirical correlations which are necessary because of the lack of theoretical background, employed in the reviewed literature are also discussed

Chapter 7 (Calorimetric Properties of Hydrothermal Solutions, V M Valyashko (Russia) and M S Gruszkiewicz (USA)), indicates the experimentally determined calorimet-ric quantities of considerable current use, gives a brief description of experimental methods for hydrothermal mea-surements and contains a summary table with information about the systems studied and the corresponding calorimet-ric measurements

Preparing this book required the talents and cooperation of

many individuals It was a long and sometimes painful

process However, it was very interesting and fulfi lling

project for me to accumulate and fi nally see the results

I would like to thank my colleagues and co-authors Dr

Ilmutdin M Abdulagatov, Dr Marc J Assael, Dr Horacio R

Corti, Dr Miroslav S Gruszkiewicz, Mrs Nataliya N

Ivanova, Dr Serguey N Lvov and Dr Donald A Palmer for

their tremendous work, initiative and their patience during

the long and diffi cult gestation of this book

We are all grateful to Dr Johanna M H Levelt Sengers

(Anneke Sengers), who played a signifi cant role in the

development of this project within IAPWS and agreed to

write a Foreword for us, and to Dr Peter G T Fogg for his

assistance in searching for a publisher

I would like to acknowledge our colleagues from

differ-ent countries for their help Since we started this project

these people donated their time, assisted with references,

fi les, publications, useful information, recommendations

and comments My sincere gratitude goes to R J

Fernandez-Prini (Argentina), T A Akhundov, N D Azizov,

N V Lobkova, D T Safarov (Azerbaijan), P Tremaine (Canada), I Cibulka (Czech Republic), K Ballerat-Busse-rolles, R Cohen-Adad, (France), J Barthel, E U Franck,

H Lentz, K Todheide, G M Schneider, H Voigt, W Voigt,

G Wiegand (Germany), Th W de Loos, C J Peters erlands), A M Aksyuk, A A Aleksandrov, I L Khodako-vsky, S V Makaev, S D Malinin, O I Martinova, A A

(Neth-Migdisov, A.Yu Namiot, T I Petrova, L V Puchkov, K

I Schmulovich, A A Slobodov, N A Smirnova, N G

Sretenskaya, M A Urusova, A S Viktorov, I V Zakirov,

V I Zarembo, A V Zotov (Russia), L Z Boshkov (Ukraine), R B Dooley, A H Harvey, P C Ho, W L

Marshall, R E Mesmer, A V Plyasunov, J M Simonson,

R H Wood (USA)

Finally, I also would like to express my thanks to my wife Luba and daughters Aliona and Katya for their constant support and understanding

Moscow

Phase Equilibria in Binary and Ternary

Hydrothermal Systems

Vladimir M Valyashko

Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, Russia

1.1 INTRODUCTION

Defi ning the phase composition of the mixture at a certain

pressure and temperature is the fi rst step in any scientifi c

investigation and obligatory information for any practical

application of that mixture

If the physical state of aqueous or any other systems at

ambient conditions can easily be determined, the phase

composition of the systems at high temperatures and

pressures should be specially studied using fairly complex

equipment

Systematic scientifi c studies of infl uence of temperature

and pressure on a phase state of individual compounds

and mixtures were begun in the eighteenth century (D

Fahrenheit, R Reaumur, A Celsius, M.V Lomonosov, A

Lavoisier, D Dalton, W Henry) However, the variety and

complexity of phase behavior at superambient conditions in

early experiments, even in two-component systems, seemed,

at fi rst, chaotic The discovery of the phase rule by Gibbs

in 1875 and the investigations of van der Waals and his

school on the equation of state and the thermodynamics of

mixture, lasting until about 1915, brought a measure of

order by providing a framework for the interpretation and

classifi cation of phase diagrams and led to a period of

intense experimental studies These pioneer publications at

the end of the nineteenth and beginning of the twentieth

centuries laid a foundation for the modern theory of

hetero-geneous equilibria and phase diagrams During the fi rst

half of the last century interest in temperature

high-pressure equilibria was quite limited and concentrated

mainly around certain aspects of power engineering and

geological problems As a result progress was not

compa-rable with the previous fi fty years; moreover knowledge

accumulated earlier gradually disappeared from the

litera-ture of physics and chemistry

The most famous discovery of that time was the

experi-mental observation of gas–gas equilibria by I.R Krichevskii

in N2 – NH3, CH4 – NH3, He2 – CO2, He2 – NH3 and in

Ar – NH3 mixtures (Krichevskii and Bol’shakov, 1941; Krichevskii, 1952; Tsiklis, 1969), that confi rmed theo -retical prediction of Van der Waals (Van der Waals and Kohnstamm, 1927) It was shown that a separation of super-critical fl uids can exist in the temperature range above the highest critical temperature of the less volatile component Another important result obtained in the last century was also connected with the critical phenomena In 1926 Kohnstamm (Kohnstamm, 1926) pointed out the theoretical possibility of fi nding a critical point ‘of second order’ in a ternary liquid mixture – a point at which three coexisting

fl uid phases simultaneously become identical In 1962–70 this point was confi rmed experimentally in two Russian aboratories (of Prof I.R Krichevskii and Prof R.V

Mertslin) (Radyshevskaya et al., 1962; Krichevskii et al., 1963; Myasnikova et al., 1969; Efremova and Shvarts, 1966,

1969, 1972; Shvarts and Efremova, 1970; Nikurashina

et al., 1971) In the 1970s such a type of phase transition,

called ‘a tricritical point’, was theoretically interpreted within a framework of ‘classical’ and ‘non-classical’ phe-nomenological models (Griffi ths, 1970; Widom, 1973; Griffi ths and Widom, 1973; Griffi ths, 1974; Kaufman and Griffi ths, 1982; Anisimov, 1987/1991)

At the same time, it was thought that the sets of phase equilibria in water-salt (electrolyte) systems were different from those in water-organic, water-gas and organic systems due to a special nature of ion-molecular interactions in aqueous electrolyte solutions In particular, the phase diagram with the two critical endpoints in solid saturated solutions was known for a long time only for systems with the molecular species (without ions) such as ether (C4H10O) – anthraquinone (C14H8O2), CO2 – diphenylamine ((C6H5)2NH) and ethylene (C2H4)) – p-chloroaniline (o-xylidin (C8H11N), o-nitrophenol (C6H5NO3), m-chloronitro-benzene (C6H4ClNO2)) (Smits, 1905, 1911; Buechner, 1906, 1918; Scheffer and Smittenberg, 1933)

However, the fi rst experimental studies of H2O – SiO2,

H2O – Na2SO4, H2O – Li2SO3 and H2O – Na2CO3 systems

Hydrothermal Experimental Data Edited by V.M Valyashko

© 2008 John Wiley & Sons, Ltd ISBN: 978-0-470-09465-5

(Kennedy et al., 1961, 1962; Ravich and Borovaya,

1964a,b,c) proved that the same phase equilibria can be

observed also in water–electrolyte mixtures

A revival of interest in hydrothermal phase behavior

occurred in the middle and second half of the last century,

sparked by the growth of chemical engineering technology

(hydrothermal crystal growth, hydrometallurgy, natural gas

and petroleum industry, supercritical fl uid extraction and

material synthesis, supercritical water oxidation for

hazard-ous waste destruction) and of fossil and nuclear power

engi-neering The main volume of experimental data for aqueous

systems at high temperatures and pressures now available

was obtained during the past 50–60 years, whereas the most

precise measurements of hydrothermal solution properties

became possible only from the 1980s onwards (Wood,

1989)

Van der Waals and his school developed the ‘classical

approach’ to phase diagram derivation, in which phase

behavior of mixtures was established by investigation of the

behavior of thermodynamic functions (free energy) in

p-V-T-x space, calculated with the equation of state Originally,

theoretical derivations of phase diagrams were done by a

topological method After the main features of a geometry

of thermodynamic surfaces (p-V-T-x dependences of

Helmholtz or Gibbs free energy) were obtained from limited

calculations available at that time using the equation of

state The following continuous transformations and

combi-nations of the geometrical features of the surfaces were

determined topologically as well as a derivation of

topologi-cal schemes of phase diagrams from the interplay of the

thermodynamic surfaces As a result of such investigations

it was established that there is a limited number of various

types of fl uid phase diagram for binary systems A

topologi-cal approach and knowledge of the regularities of phase

behavior and intersections of thermodynamic surfaces for

various phases (included the solid phase) permitted

deriva-tion of not only several types of fl uid phase diagrams but

also of the schemes of phase diagrams with solid phase

(Roozeboom, 1899, 1904; Tammann, 1924; Van der Waals

and Kohnstamm, 1927) In contrast to the term ‘fl uid phase

diagrams’, which means the phase diagrams, which describe

the phase behavior of mixture without solid phase, the term

‘complete phase diagrams’ is for the diagrams which display

any equilibria between liquid, gas and/or solid phases in a

wide range of temperature and pressure

Since the fi rst publication of Scott and van Konynenburg

in 1970 on global phase behavior of binary fl uid mixtures

based on the Van der Waals equation of state, the classical

approach to the derivation of phase diagrams has changed

from topological method to analytical method The

analyti-cal method of derivation for various liquid-gas equations

of state shows the same main types of fl uid phase behavior

for different kind of molecular interactions and the same

sequences of transformation of one type of binary phase

diagram into another due to continuous alteration of mo

-lecular parameters in the equations of state (Scott and van

Konynenburg, 1970; Boshkov, 1987; Deiters and Pegg 1989;

van Pelt et al., 1991; Harvey, 1991; Kraska and Deiters,

1992; Yelash and Kraska, 1998, 1999a,b; Thiery et al., 1998;

Yelash et al., 1999; Kolafa et al., 1999) Most of the types

of fl uid phase behavior described by Van der Waals and his school as well as by recent experimentalists can be recog-nized in analytically derived global phase diagrams Those diagrams describe (in the coordinates of molecular param-eters of each model) the regions of different types of fl uid phase diagrams generated from the equations of state.Due to the absence of a general liquid-gas-solid equation

of state such analytical method would not work for tion of phase equilibria with solid phases To do so either simultaneous investigation of two equations of state (for liquid-gas and for solid phases) should be considered or the usage of the topological method at the level of topological schemes of phase diagram rather than at the level of thermo-dynamic surfaces Modern knowledge of phase diagrams construction allows us to classify the main types of dia-grams and to defi ne a few regularities of transformation of one type of phase diagram into another

deriva-This chapter reviews general characteristics of phase behavior in sub- and supercritical binary and ternary aqueous systems obtained in theoretical and experimental studies It starts with a brief presentation of the main experimental methods employed to study the hydrothermal phase equilibria

The major body of the chapter provides an overview of recent developments in our understanding of binary and ternary phase diagram construction based on modern theo-retical approaches to phase diagram derivation and on the available experimental data In case of binary system special attention is drawn to the method of continuous topological transformation of phase diagrams and to a demonstration of systematic classifi cation of complete phase diagrams, which describe all possible types of phase behavior in a wide range

of parameters The main types of binary phase diagrams are represented by topological schemes illustrated by experi-mental results

Methods of topological schemes for fl uid and complete phase diagrams derivation and main features of phase behavior at sub- and supercritical conditions for ternary systems are discussed later in the chapter The available experimental data are used to demonstrate some regularity

of solid solubility, liquid immiscibility and critical behavior

in ternary mixtures

The original experimental data on phase equilibria bility of solid in fl uid phases, heterogeneous fl uids, liquid-gas (vapor) equilibria, immiscibility of liquids and critical phenomena) at elevated temperatures (mainly above 200 °C) and pressures are presented in Appendix 1.1 The values were extracted from the papers in national and international journals, monographs and collected articles, as well as from the deposited materials, reports and dissertations For litera-ture search, besides the Chemical Abstracts Data Base, the database system ELDAR (Prof J Barthel, Institute for Physical and Theoretical Chemistry, the Regensburg Uni-versity, Germany) (Barthel and Popp, 1991) and the data-bank for water-organic systems (Prof N.I Smirnova, Prof A.I Viktorov, Department of Physical Chemistry, the St Petersburg University, Russia), the following reference books were used (Seidell, 1940, 1941; Seidell and Linke,

(solu-1952; Pel’sh et al., 1953–2004; Linke and Seidell, 1958;

Timmermans, 1960; Kogan et al., 1961–63, 1969, 1970;

Kirgintsev et al., 1972; Valyashko et al., 1984; Buksha and

Shestakov, 1997; Harvey and Bellows, 1997) However, the

main volume of bibliography were obtained from references

in ordinary papers and reviews

This information, arranged in alphabetical order of

non-aqueous components is presented in the Summary table

(Table 1.1) Each line of the Summary table contains brief

information (types of studied phase equilibria, experimental

methods, ranges of studied temperature, pressure and

com-position) about the experimental data obtained for one

system or several relevant systems from the publication(s)

and collected in Appendix 1.1

1.2 EXPERIMENTAL METHODS FOR STUDYING

HYDROTHERMAL PHASE EQUILIBRIA

Over the years different experimental techniques at high

parameters of state were implied to study phase behaviors

(Tsiklis, 1968, 1976; Laudise, 1970; Ulmer, 1971; Jones

and Staehle, 1976; Styrikovich and Reznikov, 1977; Isaacs,

1981; Garmenitskiy and Kotelnikov, 1984; Zharikov et al.,

1985; Sherman and Tadtmuller, 1987; Ulmer and Barnes,

1987; Byrappa and Yoshimura, 2001; Hefter and Tomkins,

2003) The purpose of this review is to summarize existing

experimental methods for studing phase equilibria in

aqueous systems over a wide range of p-T-x parameters, to

describe briefl y major features of experimental procedures,

and to provide examples of the method related apparatus

along with their advantages and limitations

Experimental methods could be considered as either

‘syn-thetic’ and ‘analytic’ or static and dynamic (fl ow) methods

In the ‘synthetic’ methods the phase transitions are studied

and the p-T parameters of phase transformations are recorded,

whereas the compositions of the coexistent phases are

deter-mined from the composition of initial mixture charged into

the cell The ‘analytic’ methods determine compositions of

equilibrium phases directly at given temperature and

pres-sure, ignoring the study of phase transitions The dynamic

(fl ow) methods are distinguished from the static ones by the

fact that at least one of the phases in the system is subjected

to a fl ow with respect to the other phase

In our attempt to classify the available experimental

methods for studying the hydrothermal equilibria there are

fi ve groups that differ in the technique of obtaining

informa-tion on phase equilibria and on coexisting phase

composi-tions at high temperatures and pressures These groups

comprise:

1 methods of visual observation of phase equilibria (‘Vis

obs.’ in Table 1.1);

2 methods of solution sampling under experimental

condi-tions (‘Sampl’, ‘Flw.Sampl’ and ‘Isopiest’ in Table 1.1);

3 methods of quenching of high temperature phase

equi-libria (‘Quench’ in Table 1.1) and of weight loss of

crystal (‘Wt-loss’ in Table 1.1);

4 method using potentiometric determination (‘Potentio’

in Table 1.1) for salt solubility measurements;

5 indirect methods – determination of discontinuities (‘break points’) in the property-parameter curves; description of the behavior of interdependent parameters and/or properties of the system during the phase trans-formation (methods of p-T, p-V, p-x, T-V, T-Cv, p-∆H

curves, ‘Therm.anal.’ and VTFD in Table 1.1).

The sixth group ‘Methods using radioactive tracers’ (‘Rad.tr’ in Table 1.1) could be added to the list However, those methods are used rarely in hydrothermal investigations due

to the environmental risk, technical problems and moderate accuracy of solubility measurements Only in the publica-tion of Alekhin and Vakulenko (1987) there is a description

of an apparatus for continuous determination of the thermal fl uid composition and salt solubility in vapor by measuring the intensity of radiation of aqueous solution without sampling or quenching There are several cases of tentative experiments on solubility measurements of sul-

hydro-fi des (Ag2S, SnS and ZnS) at elevated temperatures (below

200 °C) (Olshanski et al., 1959; Nekrasov et al., 1982) and

in temperature gradient conditions (Relly, 1959) In some cases the radioactive tracers are used only to determine the concentration of samples obtained by the method of sam-

pling or quenching (Ampelogova et al., 1989) The

experi-mental studies of isotope partitioning in hydrothermal

systems (e.g Shmulovich et al., 1999; Driesner and Seward, 2000; Chacko et al., 2001; Horita and Cole, 2004 etc.) are

relevant to isotope chemistry in aqueous reactions but do not pursue the goal of phase equilibria determination and will be not discussed in this chapter

Certainly, this classifi cation is largely arbitrary and not exhaustive because in reality experimental methods are highly diversifi ed and often contain the combinations of various techniques in one run For instance, the measure-ments using the visual cell with a movable piston (for chang-ing the inner volume of the vessel and for separation of the studied mixture from the pressure medium) (see Figure 1.1) permit us to observe the phase transformation, to determine the break points (corresponding to the phase transition) on the pressure versus temperature isochore or on the pressure versus volume isotherm for the known composition and to sample the equilibrium phases at predetermined tempera-tures and pressures (Lentz, 1969 etc.) The apparatus, described by Khaibullin and Borisov (1965, 1966), permits

us to determine both the density and composition of ing liquid and vapor solutions (at temperatures up to 450 °C and pressures up to 40 MPa) by measuring intensity of the g-ray beams (pass through the bomb on different levels from the outside radioactive sources) (‘g-ray’ in Table 1.1) and by sampling the equilibrium phases

coexist-Besides methods which involve determination of phase compositions of equilibrium associations, other approaches

to phase equilibria studies are possible An example is the special method for determining the vapor pressure of solu-tions with a given composition (‘Vap.pr.’ and ‘Vap.pr.diff’

in Table 1.1) In such apparatus the composition is not measured but taken from the initial charge, whereas the vapor pressure is measured directly with a pressure gage

(Mashovets et al., 1973; Bhatnagar and Campbell, 1982;

Table 1.1

st column), the studied types of phase equilibria –

accompanied by ‘??’ is questionable. Types of phase equilibria: Soly

equilibrium L-G-S) or used for measurements (such as in the isopiestic molality measurements (LGE; isop-m)). H-Fl