TECHNOLOGY
Timing Whilst significant contamination can be generated during active mining , it tends to peak immediately after mine closure , as accumulated oxidation products are flushed out of the rock mass on flooding the mine . These then decline exponentially over a number of years to a residual value which typically remains stubbornly higher than pre-mining concentrations . For example , the iron concentration in water from the flooded Wheal Jane
“ Whilst significant contamination can be generated during active mining , it tends to peak immediately after mine closure ”
– Dr Richard Coulton , CEO
Mine in Cornwall , UK , peaked at several thousand mg / l when the mine first flooded and over the subsequent 20 years declined to less than 70mg / l .
Whilst the flushing period can be relatively short , the long-term legacy may need treatment for decades to come . For example , at Parys Mountain North Wales ( one of the largest copper mines in the world in the 1800s ), the dissolved iron concentration in the water still seeping from the mine exceeds 500mg / l nearly 200 years after closure . Whilst this concentration is exceptionally high , and reflects historical mining practices which had little regard for environmental issues , it ’ s a sobering indication of the potential long-term legacy from uncontrolled mining .
With the length of the flushing period and the residual contamination concentrations difficult to predict , it ’ s often advisable to operate a temporary treatment system post closure , until the long-term contamination load , and best treatment strategy , can be determined .
Beyond this , given the variability in water quality , different treatment options may need to be adopted during the active ,
18 December 2017