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Acid Mine Drainage is mine wastewater normally containing high levels of iron
as a result of the oxidation of pyrite. This wastewater is acidic having a pH
range of between pH 1 and 6. Depending on the mineralogy of the area in
question, acid mine drainage might contain elevated levels of dissolved metals,
such as coper, zinc,lead and etc.. These metals pose danger to the environment
due to their toxic effects on aquatic, animal and human life. This paper looks at
the removal of copper from acid mine drainage using Ion Exchange method to
less than 1mg/l. A weak acidic cation resin was used to remove copper ions
from the mine acid drainage to less than 1 mg/l. Spectrophotometric
determination of copper with sodium diethyldithiocarbamate was used to
determine the copper concentrations in the treated water.
The experimental results indicate that Acid mine drainage and other forms of
wastewater can be well be treated using ion exchange resins. The most
important thing is to establish the optimum conditions under which the resin
can perform best.
Resin sample D401 is a weak acid cation resin. The degree of dissociation of a
weak acid resin is strongly influenced by the solution pH. Consequently, resin
capacity depends on solution pH. For this reason resin sample D401 operated
well at pH 3.85 and above. At pH 6.62, which was the highest, the resin
continued to operate well achieving removal of 89.5% for the acid mine
drainage sample 2 from Hongtoushan mine. However above a certain pH level,
the copper ions would precipitate as hydroxides and ion exchange would be of
no use. Below pH 3.0 resin sample D401's exchange capacity was affected and
for this reason performed not well. This is evident when the pH was reduced
further to pH 2.5, resin sample D401 performed even worse. This happens
because hydrogen in the acid at pH below 3.85 has more affinity to the resin
than the copper ions.
The flow rate of the wastewater (acid mine drainage) is another condition
which must be well ascertained. The lower the flow rate the longer it takes for
the treated water to reach the set standard (1mg/l in this case) and Vice versa.
Optimal flow rate is required in order to get best treatment results (a lot of
water treated to the required standard in a specified time). Too low a flow rate
might result into long treatment periods and consequently demand for more
treatment and labor hours. So in practical a more suitable flow rate must be
established. Note that the flow rate used is actually the rate of flow of the
treated water.
The lower the wastewater concentration, the longer it takes for treated water to
reach the required standard concentration and therefore the more the water
treated. And the opposite is the truth in the above sentence. Therefore
wastewater concentration must be well measured before the start of the
treatment process. Too high copper concentration requires pretreatment first or
a higher resin height. Low concentrations might require reduced resin height.
The results for this experiment indicate that acid mine drainage can be treated
well by ion exchange resins, but it is also very important to establish suitable
operating conditions.