Maquinaria de movimiento de tierras

The principle of solvent extraction—the distribution of chemical species be- tween two immiscible liquid phases—has been applied to many areas of chemis- try. A typical one is liquid partition chromatography, where the principle of solvent extraction provides the most efficient separation process available to organic chemistry today; its huge application has become a field (and an indus- try!) of its own. The design of ion selective electrodes is another application of the solvent extraction principle; it also has become an independent field. Both these applications are only briefly touched upon in the chapter of this book on analytical applications (Chapter 14), as we consider them outside the scope of

this work. Nevertheless, fundamental research on solvent extraction will provide further important input into these two applications. It is likely that fundamental solvent extraction research will continue to contribute to the development of further selective analytical techniques.

The driving force of the transport of salts, proteins, etc., through the cell membrane from the nucleus to the body fluids, and vice versa, is a complicated biochemical process. As far as is known, this field has not been explored by traditional solution chemists, although a detailed analysis of these transfer pro- cesses indicates many similarities with solvent extraction processes (equilibrium as well as kinetics). It is possible that studies of such simpler model systems could contribute to the understanding of the more complicated biochemical pro- cesses.

Solvent extraction deals with the transport of chemical substances from one phase into another one, the chemical kinetics of this process, and the final equilibrium distribution of the substances between the two phases. Such trans- port and distribution processes are the motors that make life in biological sys- tems possible. Fundamental studies of such “solvent extraction” processes con- tribute to the better understanding of all processes in nature. Here, only the lack of imagination stands in the way of important new scientific discoveries.

1.5.8

Conclusion

Solvent extraction is a mature technique in that extensive experience has led to a good understanding of the fundamental chemical reactions. At the same time, compared to many other chemical separation processes like precipitation, distill- ation, or pyrometallurgical treatment, the large-scale application of solvent ex- traction is, nevertheless, a young technique. New reagents are continually being developed, spurred on by computer modeling, and more efficient contacting equipment is coming into use. Considering such factors as demands for higher product purity, less pollution, and the need for recovering substances from more complex matrices and more dilute resources, the efficiency and high selectivity of solvent extraction should make it an increasingly competitive separation pro- cess both in research and in industry.

1.6

HOW TO USE THIS BOOK

The first part of the book contains basic solution theory and thermodynamics

(Chapter 2); a survey of the effects on the distribution ratio of changes in param-

eter values, such as concentration of metals, complex formers and other reac- tants, pH, temperature, etc., (Chapter 3); measurement techniques, data collec- tion, evaluation, and interpretation (Chapter 4); and kinetics (Chapter 5). The ionic strength is an essential factor in all aqueous systems, and how to cope

with it is treated in a fundamental way inChapter 6. These chapters sometimes go into such depth that they may mainly interest only the theoretical chemist or professional engineer; in some chapters we offer some choice by placing the most detailed parts in smaller type. It is not necessary to read these chapters before the applied ones, and some can be read independently, before or after the other more applied chapters.

The second part deals with applications of solvent extraction in industry, and begins with a general chapter (Chapter 7) that involves both equipment, flowsheet development, economic factors, and environmental aspects. Chapter 8is concerned with fundamental engineering concepts for multistage extraction.

Chapter 9describes contactor design. It is followed by the industrial extraction

of organic and biochemical compounds for purification and pharmaceutical uses

(Chapter 10), recovery of metals for industrial production (Chapter 11), applica-

tions in the nuclear fuel cycle (Chapter 12), and recycling or waste treatment

(Chapter 14). Analytical applications are briefly summarized inChapter 13. The

last chapters,Chapters 15and16, describe some newer developments in which the principle of solvent extraction has or may come into use, and theoretical developments.

Apart from the first six chapters, each chapter has been written more or less independently but, we hope, consistently.

1.7

SOLVENT EXTRACTION NOMENCLATURE

Because scientists and engineers in chemistry use different symbols, a single set valid for all chapters in this book is not feasible. Moreover, it is desirable that both groups be familiar with the symbols used within the subfields in order to enhance communication. The symbols in this book closely follow IUPAC recommendations (see reference list). In the Appendix of this book, lists are given of the most commonly used symbols, except for those in Chapter 9, which has its own list of symbols.

1.8

LITERATURE ON SOLVENT EXTRACTION

Recommendations of solvent extraction terminology have been published by the International Union of Pure and Applied Chemistry (IUPAC) [1,3–5]. Some excellent monographs on solvent extraction are listed in section 1.8.1; unfortu- nately, the older ones may only be available in large science libraries. Most of them deal either with a small sector of the field or are very comprehensive. Finally, in section 1.8.2, we have collected edited versions of proceedings of the International Conferences of Solvent Extraction (ISEC), which normally are held every three years.

Because solvent extraction is used extensively as a technique in research, publications with this technique appear in all types of chemical journals. This is also true for its industrial applications that are often described in chemical engineering journals.