kaolin and zeolite are clay minerals that are easy to obtain, but that depends on the use your are thinking about the one you need (If you want to use as heavy metals sorbent, as a geological barrier, impermeabilization layer....) both have significant differences as a sorbant. The price depends on the quantity and te purity grade you need for yor lab / field experimental work.

Thanks Millán,

What about replaced by Activated Carbon as adsorbent.

It is an option, but if your work it is focused on heavy metales, you can test and compare in a previous simple test lab test (column, batch,...) clay or clay minerals (zeolite, kaolin, bentonite) and active carbon. I recommended to use referenced /certified material or some solution with a marked element in order to calculate the sorption rate. Finally, there is a sorbent that can be use depending on the contaminant you want to bind or fix and if you want to remove from a solution for it final disposal, it is the "fly ash". Fly ashes are a waste from coal combustion that can be use as a sorbent, they are cheap and you can give an use to a residue. As I told before, that depend on the mein objective of your work, the contaminat you want to remove or fix, and the initial matrix you are goingo to work with.