## 4 Conclusions  
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. Testing as supplementary cementitious material (SCM) for composite cements and as raw material in autoclaved aerated concrete (AAC) showed a potential for the valorization in both products. The detoxified SPL was characterized as a partially amorphous aluminosilicate, which after milling showed a moderate reactivity in the R3 heat release test. A cumulative heat release of 200 J/g was obtained after 7 days, which is similar to class F coal fly ashes. When the SPL was mixed in a Portland cement blend, a delay of cement hydration was observed. By 7 days the cumulative heat of the SPL-cement paste caught up with the inert quartz-cement paste. No changes in the hydration product assemblage were observed, but an increased Ca(OH)\({}_{2}\) consumption by SPL was detected by 28 days. Mortars showed a significant decrease in compressive strength at 2 days when SPL was used as SCM, but the strength activity index was seen to increase in time, showing that the SPL contributed additional strength by 28 and 90 days. This suggests that cement blends including SPL are promising to be used in general purpose concrete, but further testing at the concrete level is required to confirm their applicability. The use in AAC blocks resulted in a retention of the density-strength relation up to a 50 wt% substitution of quartz for SPL. The production of blocks with 600 kg/m\({}^{3}\) and compressive strength of 4 MPa was achieved for these 50 wt% quartz substituted mixes, fulfilling the strength requirements of the medium density type AAC masonry block according to EN771-4. Overall, the use of SPL aluminosilicates was shown to be promising in both applications and the presented work provides a basis for further optimization and technoeconomic studies targeting specific locations and production plants.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11083715/s1](https://www.mdpi.com/article/10.3390/app11083715/s1)]([https://www.mdpi.com/article/10.3390/app11083715/s1](https://www.mdpi.com/article/10.3390/app11083715/s1)), Figure S1: Comparison of the diffractograms of cement pastes with 30 wt% spent pot lining aluminosilicates and 30 wt% of quartz filler at 7 and 28 days, Figure S2: X-ray diffractograms of the samples with 30 wt% quartz filler and 30 wt% spent pot lining aluminosilicates at 7 and 28 days.  
Conceptualization, A.P., M.K., R.S., A.M. and L.H.; Data curation, A.P. and M.K.; Formal analysis, A.P. and R.S.; Funding acquisition, A.M. and L.H.; Investigation, A.P.; Methodology, R.S., A.M. and L.H.; Project administration, M.K. and L.H.; Resources, M.K.; Supervision, M.K., R.S., A.M. and L.H.; Visualization, A.P.; Writing--original draft, A.P. and M.K.; Writing--review & editing, R.S., A.M. and L.H. All authors have read and agreed to the published version of the manuscript.  
The research in this paper was carried out in the project \"SPL-Cycle: Closing the loop of the Spent Pot-line (SPL) in the Al smelting process\", a KIC Added Value Activity funded by the European Institute of Innovation and Technology (EIT) Raw Materials (project number 17141). EIT is a body of the European Union and receives support from the European Union's Horizon 2020 Research and Innovation Programme.  
Not applicable.  
Data Availability Statement: The data presented in this study are available on request from the corresponding author.