Use of cement minerals as remediation materials

This is a three-year award available to start 1st September 2017. This is a tax-free stipend covering tuition fees and living expenses at the standard EPSRC rate (commencing at ~£ 14,296 per year).

The proposed project is: Use of cement minerals as remediation materials.

Overview
Cement is a complex material consisting of both crystalline and amorphous phases. Due to the chemical properties of cement systems, e.g. high internal pH as well as the amorphous and crystalline component phases, foreign ions may be accommodated in this system and as such it is a well-studied material for waste remediation and encapsulation.

Ettringite, a known mineral phase, forms rapidly during hydration processes in the production of cement. Its concentration increases to a maximum one day after the hydration has commenced and then decreases and may even approach zero as the sulphate concentration decreases. Ettringite can subsequently form through sulphate attack of the cement, a process known as delayed ettringite formation; this is detrimental to the integrity of the cement. The crystal structure of ettringite can be thought of as consisting of cation columns Ca3[Al(OH)6.12H2O]3+, that run parallel to the c axis, with the sulphate anions and remaining water molecules in channels running parallel to these columns . Its crystal structure can accommodate a wide range of both cations and anions. Studies to date have focussed mainly on the sulphate anion replacement in ettringite, with reports of ettringite phases forming with many anions, e.g. NO3-, B(OH)4-, SeO42-, SeO32-. OH-, SO32-, CrO42-, CO32-, Cl-, ClO3- .

It is this property of ettringite, coupled with its central role in cement chemistry, that makes it an ideal candidate for the immobilisation of many heavy metals, metalloid species and encapsulation of radionuclides in concrete matrices. Understanding the exact mechanisms of immobilisation of these ions in concrete matrices through studying the structures and properties of the individual cement phases is recognised as an area for further study.

Aims
• Synthesise targeted compositions, such as ettringite type phases (Ca6[Al(OH)6.12H20]2(SO4)3.2H2O),
• Replace Al for other cations, e.g. Fe, Ga, Mn, Sn, Co, Cr
• Replace sulphate with other anions, such as nitrate, halide, phosphate, arsenate.
• Characterise phases using powder X ray diffraction, infrared spectroscopy, thermal analysis and electron microscopy techniques.
• Characterise structures and investigate stability of materials under different conditions of pH and temperature.
• Use powder X ray diffraction methods to monitor processes in situ through development of flow cells for use in house and at central facilities such as the Diamond Light Source.

Dr Kirk’s current projects:
Development of thin film Ni(OH)2 electrochromic materials.
Incorporation of Co into synthetic Fe oxyhydroxide systems – implications for natural systems.
Stability of radionuclide containing materials – implications for remediation of contaminated sites.



Dr Kirk’s current projects:
Development of thin film Ni(OH)2 electrochromic materials.
Incorporation of Co into synthetic Fe oxyhydroxide systems – implications for natural systems.
Stability of radionuclide containing materials – implications for remediation of contaminated sites.