Yes, used in making ceramic filters. Mixing clay with for example rice husks and then burning the clay in a furnace carbonizes the rice husks and tiny pores are created inside the clays and can be used as a ceramic filter. if the rice husk is ground to the microscale/nanoscale, then the product can be used in industrial pollution control e.g. removal of colored effluents in textile processing.

Clay supported membranes and used for removal of various pollutants like metal ion, oily wastes and other macro particles and thus may used as adsorbent.

if you search online for "clay in pollution control" you will get a selection of useful  (AND useless) references to read.

Dear Dr. Sagaya,

I think you asked for modified clay adsorbents. Attached an article of Srinivasan & Fogler, 1990 (maybe you know already). They attached to Na-Montmorillonite cetylpyridinium chloride (CPC) as an adsorbent for 3,5-DCP, etc. That is somehow similar to flotation collectors with often have an organic and an inorganic component.

Yes, Clay can be used as adsorbent for pollutants. But this is applicable up to some extent and particularly for few contaminants. It has numbers of limitations and assumptions.

If fact most clays adsorb heavy metals in aqueous solutions. I know of cases where the clay - nontronite is used to extract hexavalent chromium. Similarly, clays such as I think kaolinite are used in removal of toxic heavy metals like Pb, Cd, etc.

I think clays are increasingly being used in "face pack" for their absorbent and detoxifying effects. That was true for 'gopichandan' or "multani mitti" which were almost natural kaolinite.

In Kutch clays are used to line ponds storing groundwater that contain fluoride. the water is aerated and left standing for a week or so and the water is subsequently used for irrigation. "Dying wisdom" perhaps.

Yes, clays can be used in wastewater treatment as adsorbent and its modified form can be used as catalyst in Advanced Oxidation processes. Clay and clay minerals, either as natural or after modification, is recognized as one of the materials of the 21st century because are abundant, inexpensive ( normaly US dollars 0.14 - 0.12/Kg, 20 times cheaper than activated carbon) and environmental friendly.  

Clays basing on their Physical and Chemical parameters and also treated clays (modified) have been in use as adsorbents for a variety of adsorbates.

Yes, Clay minerals, specially montmorilonite (smectite)  used in remediation technique because of their high CEC. You can search bentonite application for remediation

Clay can be used as a geo-membrane where lack of clay and materials are sand polluted water can easily penetrate. 

clays trap all kinds of cations by nature negatively charged

Clays are excellent materials for the cleanup. The numerous academic scientific works prove that. However, at the level of the industry, the latter are not used yet. Probably, the management of this waste (clays + pollution) is not still well mastered!

Yes.

Clay minerals,in particular, montmorillonite which can be used is an adsorbent material for removal heavy metals from aqueous solutions. 

Can be used in fabrication of water filters for cleaning water for domestic use in rural areas

Can be used as a geo-membrane  of cover part of sand body .