*2.5. Metallic Aluminum*

Metallic Aluminum was measured by oxidation of Al<sup>0</sup> with H2O at high pH conditions (Equation (5)) by measuring the amount of produced gas and calculating Al0 using the ideal gas law.

$$\rm Al^{0} + 3H\_{2}O \rightarrow Al(OH)\_{3} + 1.5H\_{2} \tag{5}$$

Theoretically, all base metals can from hydrogen in contact with water. A solution of 100 mL 0.5 M NaOH(Merck & Co., Kenilworth, NJ, USA) was filled in a Schott laboratory bottle (1 L) from Smilax and flushed with Ar gas for ~5 min to create an inert atmosphere. FA (25 g) and a magnetic stirring device (300 rpm) were added to the solution, and the bottle was immediately closed and sealed. Temperature and pressure in the thermally isolated bottle were recorded every 10 s by a P/T logger (HOBO U20-001-01, Onset, Cape Cod, MA, USA) for at least 8 h until reaction equilibrium was reached.

### *2.6. Cluster Analyis*

To analyze similarities among FA, a data set with the obtained values of Zn, Al0, ANC, and the amount of produced FA was compiled. The cluster analysis was done in MATLAB (R2018a, MathWorks, Natick, MA, USA, 2018) using the linkage function to calculate an agglomerative hierarchical cluster tree.
