A method for removing metal contaminants from acidic mine wastewater using lignin
derivatives, such as lignosulfonates and kraft lignin, an alkali coagulant, such
as a lime compound, and an alkaline composition for increasing the pH. The lignin
derivatives are dispersed in the wastewater and the coagulant is added, increasing
the pH to about 4.5-8.5 and causing the formation of a floc. The alkaline composition
is then added to bring the pH to about 9 to 10, causing the further formation of
a floc. Optionally, air oxidation is carried out, reducing the pH to about 8.1-8.6.
Optionally, a ferric or ferrous salt may also be added. The flocs comprise metal-lignin
colloids, metal hydroxides and metal salts. The flocs coagulate to form a sludge.
Optionally, fly ash or diatomaceous earth may be added to increase the density
and stability of the sludge. The sludge that is formed contains the metals and
is separated from the treated water by filtration.