Remediation of Abandoned Metal Mine Drainage using Dealginated Seaweed

This thesis develops and demonstrates an innovative method for adsorbing metals frommetal mine drainage in mid-Wales and northern Italy using dealginated seaweed (DS) as abiosorbent. The chemical composition of 15 mine drainages and two receiving waters inWales was determined over a two year period in relation to precipitation and season. Thewaters were circum-neutral, iron-poor (<1 mg/L) but metal-rich, dominated by Zn ( 42mg/L), Cu ( 188 μg/L), Cd ( 99 μg/L) and Pb ( 2.7 mg/L). The chemical compositionvaried 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 % ofZn, Cd and Pb were removed from solution within 15 minutes of contact; adsorption wasnot affected by pH (between 3.3 and 6.6) nor by additional elements in solution. Theadsorption capacity of the DS was Pb > Cd > Zn. The main removal mechanisms weredetermined to be adsorption and ion exchange with Ca, Na, Mg released from the DSsurface.Treatment plants containing DS were deployed at three sites in mid-Wales and one site inItaly. 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. Thesaturation of the DS was dependent on the mine drainage composition, with adsorptioncontinuing for several months when low metal concentration (<1 mg/L) mine drainageswere 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 theDS treatment plant to remove the remaining metals.The treatment plants improved the quality of mine drainage and reduced their impact onreceiving water courses; the plant was designed to be a practical, low-cost, solution whichuses a waste product (from the alginate industry). This thesis demonstrated a novelmethod for remediation of neutral, low Fe waters, and is applicable as a final ‘polish’ whenacidic, Fe-rich water has been neutralised and the Fe removed.

EU-LIFE Environment project “BIOMAN”(LIFE03/ENV/UK/000605)