For the Mercury, please compare the Outside Temperature with the melting Point.
Should the Biome you are in not have a sufficiently cold Temperature, you will need an electric Cooler to cool down the Mold further. This is the reason why the Mold will not prevent you from filling it with Mercury.
As for the Sifting Table, are you sure there is no other Item in its Input Slot? Something like, I dont know, 1 tiny purified Ore, that cant be sifted until 9 are present? For that Table it is a good idea to craft 9 Piles together into one big Pile, yes you can craft that (see its Tooltip).