Science, Technology and Engineering

Environmental Geoscience

Honours Projects

Geochemical Characterisation and Arsenic Remediation of Mine Discharge Water at the Glen Wills Historic Mining Area, Victoria

Andrew Nelson

Supervisor: Dr John Webb

The Maude Mine, in the historic Glen Wills mining region of north-eastern Victoria, lies within alpine highlands and is characterised by rugged topography, high rainfall, and low evaporation. The Mount Wills Granite, a plutonic intrusion into the Paleozoic country rock, has an associated mineralized zone containing gold, which has been mined by a network of adits and shafts which date back as early as 1850. The ore body is characterised by arsenic-containing sulphide minerals (arsenopyrite) as a common gangue phase, and consequently mine drainage in the underground workings contains elevated concentrations of arsenic; upwards of 1800ppb.

Since commercial operations ceased in 1950 the historical workings have been completely submerged by infiltrating groundwater. Before the mine can be reopened and ore extraction can recommence, the historical workings must be dewatered, with a view to disposing of the contaminated mine water into the adjacent Glen Wills Creek.

In Victoria arsenic concentrations of any wastewater release into natural waterways must not exceed the ANZECC guideline boundary of 13 ppb. Hence, in order to comply with these guidelines the wastewater from the dewatering program must be treated prior to its disposal.

To determine the most practical and cost effective method of treatment, a number of bench-scale trials have been performed, testing commercial products which utilise the enhanced coagulation, fixed-bed adsorption, and ion exchange methods of arsenic removal. Fixed-bed adsorbents (activated alumina and granular ferric oxyhydroxide) and ion exchange resin displayed a relatively poor efficiency for arsenic removal. However, the coagulating agents poly-aluminium chloride and ferric chloride reduced arsenic concentrations to =13 ppb; achieving 100 percent arsenic removal efficiencies, whilst utilising the method of enhanced coagulation and minimum dose rates of 7.1 mg/L and 16.3 mg/L respectively. This treatment procedure generated a substantial amount of sludge that is classified by the EPA as class A prescribed waste, with an average of 31.61 mg/L (poly-aluminium chloride) and 29.39 mg/L (ferric chloride) produced.

Estimates for the total annual cost of each coagulant were calculated to be $15,900 (poly aluminium chloride) and $19,500 (ferric chloride); based on an estimated dewatering rate of 1 ML/day, and a reduction of arsenic concentrations in treated water to negligible levels.

This project was supported by Australian Goldmines and Synergy Metals.