Most of these calcined clay type substrates (turface, safetsorb, oildry, kitty litter, flourite, etc.) just provide an inert (won't dissolve/breakdown/affect H2O chemistry, etc.) substrate that has a high Cation Exchange Capacity (CEC).
This means that cations will temporarily bind to the substrate, and from there the plants can make use of them.
So the substrate is inert, and doesn't contain nutrients itself, but helps convey nutrients in the watercolumn (or added to the substrate) to the plant via the roots.