Abstract:
This thesis develops and demonstrates an innovative method for adsorbing metals from
metal mine drainage in mid-Wales and northern Italy using dealginated seaweed (DS) as a
biosorbent. The chemical composition of 15 mine drainages and two receiving waters in
Wales was determined over a two year period in relation to precipitation and season. The
waters were circum-neutral, iron-poor (<1 mg/L) but metal-rich, dominated by Zn ( 42
mg/L), Cu ( 188 μg/L), Cd ( 99 μg/L) and Pb ( 2.7 mg/L). The chemical composition
varied throughout the year, but did not necessarily show clear seasonal variation, with Zn,
Cd and Pb tending to show a winter maximum.
The physico-chemical adsorption characteristics of the DS were determined. Over 80 % of
Zn, Cd and Pb were removed from solution within 15 minutes of contact; adsorption was
not affected by pH (between 3.3 and 6.6) nor by additional elements in solution. The
adsorption capacity of the DS was Pb > Cd > Zn. The main removal mechanisms were
determined to be adsorption and ion exchange with Ca, Na, Mg released from the DS
surface.
Treatment plants containing DS were deployed at three sites in mid-Wales and one site in
Italy. In mid-Wales, Zn, Pb and Cd adsorption peaked within an hour (at ~98 %)
associated with a significant release of Ca, Mg and Na. The DS adsorbed Pb > Cd > Zn,
with the DS adsorbing ~1 % of its dry weight of Pb, ~0.01 % Cd and ~2 % Zn. The
saturation of the DS was dependent on the mine drainage composition, with adsorption
continuing for several months when low metal concentration (<1 mg/L) mine drainages
were remediated. In Italy, acidic (~pH 2.5), metal-rich ( 120 mg/L Al, 420 mg/L Fe and
99 mg/L Cu) mine drainage required neutralisation and Fe-removal before entering the
DS treatment plant to remove the remaining metals.
The treatment plants improved the quality of mine drainage and reduced their impact on
receiving water courses; the plant was designed to be a practical, low-cost, solution which
uses a waste product (from the alginate industry). This thesis demonstrated a novel
method for remediation of neutral, low Fe waters, and is applicable as a final ‘polish’ when
acidic, Fe-rich water has been neutralised and the Fe removed.
