Detoxified Spent Pot Lining from Aluminum Production as (Alumino-)Silicate Source for Composite Cement and AutoClaved Aerated Concrete

Arne Peys,Liesbeth Horckmans,Ruben Snellings,Ana Mladenovič,Mateja Košir

doi:10.3390/app11083715

Arne Peys, Liesbeth Horckmans + Show 3 more

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https://doi.org/10.3390/app11083715

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Abstract

New sources of supplementary cementitious materials (SCMs) are needed to meet the future demand. A potential new source of SCM is spent pot lining, a residue from aluminum production. The present work showed that the refined aluminosilicate part of spent pot lining (SPL) has a moderate chemical reactivity in a cementitious system measured in the R3 calorimetry test, comparable to commercially used coal fly ash. The reaction of SPL led to the consumption of Ca(OH)2 in a cement paste beyond 7 days after mixing. At 28 and 90 days a significant contribution to strength development was therefore observed, reaching a relative strength, which is similar to composite cements with coal fly ash. At early age a retardation of the cement hydration is caused by the SPL, which should most likely be associated with the presence of trace amounts of NH3. The spent pot lining is also investigated as silica source for autoclaved aerated concrete blocks. The replacement of quartz by spent pot lining did not show an adverse effect on the strength-density relation of the lightweight blocks up to 50 wt% quartz substitution. Overall, spent pot lining can be used in small replacement volumes (30 wt%) as SCM or as replacement of quartz (50 wt%) in autoclaved aerated concrete blocks.

Highlights

Spent pot lining (SPL) is a hazardous waste originating from the production of aluminum [1,2]
This study evaluated whether spent pot lining (SPL) aluminosilicates could be used as raw material in the construction industry after detoxification and extraction of fluoride salts
A cumulative heat release of 200 J/g was obtained after 7 days, which is similar to class F coal fly ashes

Summary

Introduction

Spent pot lining (SPL) is a hazardous waste originating from the production of aluminum [1,2]. In the Hall–Héroult process, aluminum is reduced electrochemically from alumina using graphite electrodes and a cryolite electrolyte. This process happens in a pot, which has to be replaced every 5 years [1,3]. During operation the pot lining is slowly impregnated with cryolite and other reaction products forming during aluminum electrolysis. Efforts have been made to introduce these spent pot lining aluminosilicates in cement production, where it can represent up to 12 wt% of the raw meal [10]. Further studies are needed to assess whether the refractory part of spent pot lining can contribute to the cement hydration reactions without negative effects on the performance, durability or environmental compatibility

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