Étude de la valorisation des brasques traitées comme liants cimentaires

Abstract

Spent pot lining from primary aluminum production (SPL) is a hazardous material generated by end-of-life electrolysis cells. The SPL is separated into two parts, the first rich in carbonaceous materials and the second rich in vitrified refractories. The treatment of the refractory part of the SPL by the industrial LCL&L (Low Caustic Leaching and Liming) process generates a non-hazardous inert residue, called LCLL Ash. With a production of 4 billion tons in 2018, concrete is one of the most consumed materials in the world. However, the concrete industry also consumes a lot of natural resources and energy, causing significant greenhouse gas emissions. One of the best solutions to reduce the environmental impact of concrete is to use supplementary cementitious materials (SCM). The objective of this thesis is to study the possibility of upgrading LCLL Ash as cementitious materials. This doctoral project is divided into three specific objectives. The first specific objective concerns the characterization of LCLL Ash, and the understanding of the impact of the addition of LCLL Ash on the properties of cementitious materials. The second specific objective of the thesis aims to study the reactivity of LCLL Ash according to standardized methods and advanced methods. The third specific objective focuses on improving the reactivity of LCLL Ash as a cementitious binder. This specific objective is divided into four sub-objectives aimed at identifying the ideal calcination temperature, and evaluating the impact of the addition of fluorite on the calcination of LCLL Ash. Finally, the last two sub-objectives respectively focused on exploratory tests to improve LCLL Ash respectively with ternary mixtures and by the synthesis of alternative cements. The study of the specific objectives showed that the LCLL Ash is a powder composed of stable crystalline phases such as albite, nepheline, corundum, and graphite residues. LCLL Ash showed filler-like behavior like quartz powder. Calcination of LCLL Ash at 1050°C showed a marked increase in reactivity with a pozzolanic behavior visible by a reactivity index similar at class N fly ash. The influence of the calcination temperature on the reactivity of LCLL Ash was then studied using the Frattini and R3 tests. With calcination temperatures ranging from 600°C to 1200°C, two behaviors could be identified. At 800°C an increase in reactivity similar to a medium reactivity fly ash was observed with a decrease in alkalis in the porous solution. For temperatures of 1000°C and above, a reactivity similar to fly ash has been observed. In order to promote the formation of an amorphous phase during calcination, the addition of fluorite, another by-product of the LCL&L process, was studied at 800°C and 1000°C according to the previous methods. At 1000°C, and with a replacement of 10% by mass of fluorite, a significant increase in reactivity was observed, with a behavior between a blast furnace slag and a class N fly ash. Beyond a 10% replacement, the excess fluorite no longer increases the reactivity of the calcined LCLL Ash. Finally, exploratory tests were conducted to assess the potential of LCLL Ash without calcination in ternary mixtures and for the synthesis of alternative cement. Ternary blends did not show improvement in LCLL Ash. The synthesis of cement based on LCLL Ash made it possible to obtain belitic cements, rich in mayenite.

Date	19 Dec 2022
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Claudiane Ouellet-Plamondon (Supervisor)