Radiotracer and soliometric investigations
Abstract
The thesis consists of two parts: the first part deals with a radiotracer study of the source of sulphur pick?up in manganese deposits obtained from a manganous sulphate (0.2 M) – ammonium sulphate (1.0 M) bath containing 0.1 g/L SO?, and the second part describes the development of a new electroanalytical technique for the determination of 14 substances.
In the radiotracer study (Chapter 1), results have been obtained on the sulphur pick?up from solutions (with and without sulphur dioxide) containing tagged sulphate, and from solutions containing tagged sulphur dioxide. From these results, it has been concluded:
That the contribution of sulphate to the sulphur incorporation in the manganese electrodeposit is unaffected by the presence of the addition agent; and
That the bulk of the sulphur in the deposit comes from the sulphate (0.058%), rather than from the sulphur dioxide (0.006%) in solutions containing 0.1 g/L of addition agent.
Evidence is also given to suggest that the sulphur incorporation from sulphate is in the form of sulphide, implying an electrochemical reduction of sulphate.
With the completion of one stage in the radiotracer study on sulphur incorporation in manganese deposits, the question of the analysis of trace amounts of sulphur dioxide was considered from the standpoint of the investigations on iodine–iodide solions being undertaken in the laboratory. The possibility of using such solions for electroanalytical purposes led to a change in the subject of study. The rationale for this alteration of objectives is discussed in Chapter 2.
Chapter 3 presents an introduction to the principles underlying the thin?layer redox cells known as solions, particularly the iodine–iodide type. Though quite elementary from an electrochemical point of view, these principles have been described for the sake of completeness.
Chapter 4 contains a discussion of the theoretical basis of the new electroanalytical technique developed in this work. This technique, which has been called soliometry, is based on the linear relationship between the limiting iodine diffusion current in a solion and the iodine concentration. Thus, the concentration of any substance reacting with the solion electrolyte and either consuming or generating iodine can be determined by measurements of the changes in the solion limiting current.
A brief discussion is presented of:
the sensitivity of soliometry,
the sources of interference, and
the relationship between soliometry and other well?known electroanalytical methods.
It is argued that soliometry may be considered a form of thin?layer amperometry with iodine as the amperometric indicator in the present study.
Chapter 4 also includes a description of the micrometer?based thin?layer apparatus used in this work and its performance with respect to iodine concentration and inter?electrode distance. The chapter concludes with a list of reducing and oxidizing agents whose soliometric determination appeared feasible based on their standard electrode potentials.
Chapter 5 is devoted to the studies carried out on the soliometric determination of the following reducing agents:
sulphur dioxide,
arsenite,
tin(II),
ferrocyanide,
antimony(III),
sulphide, and
thiosulphate.
The determination of the following oxidizing agents forms the subject matter of Chapter 6:
selenite,
hydrogen peroxide,
iodate,
dichromate,
copper(II),
available chlorine, and
persulphate.
The same pattern has been adopted for describing the studies on each of the above 14 substances. This pattern consists of:
A brief introduction to the common electroanalytical methods (potentiometric, conductometric, polarographic, amperometric and coulometric) and spectrophotometric methods used for their determination;
A procedure for the soliometric determination;
The experimental results obtained using the procedure; and
An assessment of the soliometric method in relation to the above?mentioned methods.
In all cases, it has been shown that soliometry is an extremely simple, inexpensive, and elegant technique, easily capable of achieving precision at the ppm level.