Generally, the extraction efficiency was directly proportional
to the sizes of the metal ions (from largest to smallest)
Pb(II) > Cd(II) > Cu(II) > Ni(II) > Mn(II). Metals of larger sizes were
highly removed whereas those of smaller sizes were the least
removed except for Cd(II), Ni(II) and Cu(II), which were reversed,
which could be due to diagonal relationship between Cd and Cu,
hence similar sizes.
The extraction by shaking was less efficient than extraction by
sonication since it showed less removal of the metals under study as
compared to the sonication method. In fact, sonication can be carried
out within a shorter period of time unlike the shaking method
which is carried out for a long period of time yet it has less efficiency