--are these different names for the same plant?--> can be ground and used as a coagulant to purify water; or they may be rubbed against the inside walls of the earthenware water containers.
Dorr (also Dorr-Oliver) - a continuous process using two tanks with recycling ("1st carbonatation") to build up particle size for natural flocculation.
Iron oxide adsorption treatment for arsenic in groundwater is a commonly practiced removal process which involves the chemical treatment of arsenic species such that they adsorb onto iron oxides and create larger particles that may be filtered out of the water stream.