Algal cell walls contain acidic polysaccharides, e.g. alginic acid in
many marine species, and pectin in fresh-water species. At neutral pH
these provide anionic sites which bind ionically to metals, and acidif
ication releases metals when covalent bonds to H are made. Added Cu re
leases an equivalent amount of Ca, Mg, H from Vaucheria, and protonate
d amines also displace metals. Interestingly, diamines, which function
as efficient growth promoters, are sorbed more strongly than monoamin
es based on Langmuir adsorption constants. Sorption of Pb and Cd on Rh
izoclonium from the solid hydroxides releases Na, Ca, Mg from the alga
and OH from the hydroxide in essentially stoichiometric amounts. Sorb
ed heavy metals can be removed by precipitation of the sulfide (Cd), h
ydroxide (Cu, Al, and Ph), or as an EDTA complex (Pb) in ion exchange
processes. Values of ion exchange constants for displacement of Ca by
Mg, Zn, Cd, Pb, and Cu on Vaucheria are independent of pH and increase
with the (charge)(2)/radius of metal ions, as also observed for K and
Al. These results indicate a non-cooperative behavior of anionic site
s which interact with these metals by electrostatic attractions. Rates
of metal desorption and ion exchange constants with alginates as mode
l systems were also investigated.