It can be concluded that the Pb extraction
ability for Akra mine tailings with simulated leachate
was significantly affected by the pH value of the
leachate. In addition the very low pH value in the
leachate from the initial and acidogenesis phases
showed the highest Pb extraction ability. While these
leachates at a pH of < 4.5 may be used as extractant,
those from the (early) methanogenesis phase, with a
pH of between 6 and 8 should not be used as an
extraction agent. In addition, the Pb extraction ability
of the leachates with a pH of more than 8
(methanogenesis phase) were too low to be of use,
especially compared to that obtained from the first
phase of fermentation. These results are somewhat
similar to those of Impellitteri et al.(15) where the Pb
extraction was greatest at low (6)
values. Pb leaching behavior can be divided into three
stages based on the leachate pH: a high alkalinity
leaching stage at pH>12, where Pb forms soluble
hydroxide anion complexes and leaches out; a neutral
to alkaline immobilization stage in the pH range of
6-12, which was characterized by low Pb leachability
caused by adsorption and precipitation; and an
acid leaching stage at a pH < 6, where the acid
neutralizing capacity was totally consumed and
therefore free Pb-ion leached out.(16)