Thesis topic proposal
Pál Sipos
Formation and structure of complex compounds in hyperalkaline aqueous solutions relevant to radioactive waste repositories


Institute: University of Szeged
environmental sciences
Doctoral School of Environmental Sciences

Thesis supervisor: Pál Sipos
Location of studies (in Hungarian): SZTE SzAKT
Abbreviation of location of studies: SZTE

Description of the research topic:

In hyperalkaline (pH > 13) aqueous solutions, Ca2+ ions form unusual solution complexes with certain organic ligands containing carboxylate and alcohol(ate) donor groups (e.g., gluconate (GLU–) and heptagluconate (HGLU–), etc.). The peculiar features of these solution species are as follows:
(i) the complexes formed are of unexpectedly high stability;
(ii) they are predominantly multinuclear (bi- or trinuclear) and
(iii) the majority of the predominant multinuclear complexes are charge-neutral.
The discovery of these novel complexes opened some new perspectives in the hyperalkaline chemistry of calcium-sugar interactions. Hydroxy-carboxylates are well known complexing agents for tri- or tetravalent metal ions, in particular for those with “hard” character. Involvement of Ca2+ ions in these complexation processes give rise to the formation of CanLmM type heteropolynuclear complexes. If we approach this from another perspective, the bi- and trinuclear Ca-complexes present in high-pH solutions serve as precursors or templates to form the ternary (heteropolynuclear) species. The strong binding of these mainly “hard” type metal ions has clear practical implications, e.g., mobilization of radionuclides like Th(IV), Cm(III), etc. in radioactive waste repositories, binding of Al(III) in the Bayer’s alumina-trihydrate production or interactions with Fe(III) in cathodic reduction of vat dyes in various dyeing processes (for more details, see below.) To describe the aqueous chemistry (including speciation, mobilization, mode of action in a given process, etc.) of these environmentally sensitive and/or practically relevant systems, the knowledge of the factors, which determine the stability, composition and structure of these species (both on binary and ternary level) is a prerequisite. Accordingly, the main aim of the project is to gain fundamental chemical knowledge on the nature of the CanLm type binary and CanLmM type ternary complex compounds forming in hyperalkaline aqueous solutions of, e.g., environmental relevance. Hyperalkalinity means extreme conditions, and under extreme conditions unusual chemical events are expected to occur.

Number of students who can be accepted: 1

Deadline for application: 2020-02-01

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