*2.4. Ca-Al LDH*

Commercial grade Ca(OH)2 (LimeCo. Minerals, JHB, GP, ZA) was first calcined at a temperature of 900 ◦C for 1 h to remove any hydroxide and carbonate impurities, to form CaO. This was then reacted with 100 mL water for 15 min to form Ca(OH)2. This step eliminated the possibility of vapor formation within the milling chamber due to the extremely exothermic CaO hydration reaction. The Ca(OH)2 and Al(OH)3 (Hindalco, Belgaum, India) were milled with and without the addition of a carbonate source, CaCO3 (Kulubrite 45, Idwala Carbonates, Port Edward, KZN, ZA). The selected metal starting ratios were Ca:Al:CaCO3 of 2:1:0 (35.80 g CaO, 16.60 g Al(OH)3)(S4) and 3:2:1 (25.93 g CaO, 15.91 g Al(OH)3, 10.58 g CaCO3)(S3) [21].
