Australia will continue to be one of the world s biggest producers of arsenic wastes as it steps up the mining of sulfide ores, particularly those containing arsenopyrite.
Arsenic-bearing wastes may take many forms, including acid mine tailings, process effluent and flue dust. Arsenic stabilisation is necessary to minimise the environmental impacts of these wastes.
In several countries such as India and Bangladesh, the ground water has elevated concentrations of arsenic, the result of dissolution of naturally occurring minerals. The people who drink this water in order to avoid surface-water diseases, display the keratosis and melanomas characteristic of chronic arsenic poisoning.
Because of this problem, the World Health Organisation has lowered its recommended maximum concentration limit (MCL) for arsenic in water to 0.01 mg/L.
The Australian Nuclear Science and Technology Organisation (ANSTO), in conjunction with the Cooperative Research Centre for Waste Management and Pollution Control has developed several advanced oxidation methods that enhance the removal of arsenic from contaminated waters.
The first of these uses the highly oxidising free radicals which arise when dissolved iron or colloidal iron hydroxides are illuminated with sunlight or short wavelength UV light from lamps. The use of iron is particularly advantageous as the colloidal iron hydroxide also has excellent arsenic adsorption properties.
This process has been demonstrated by ANSTO staff to remove arsenic from acid mine drainage waters in Montana, USA, and from drinking water in Sonargaon, Bangladesh. In the second method, sulfur dioxide or sodium sulfite is used to absorb short wavelength UV light from germicidal lamps which increases the efficiency of the process in groundwaters.
In Bangladesh, the iron-solar process, which requires no electricity, was further developed so that households could treat their own daily water supplies. Using simple trays and a custom designed settling urn the arsenic was reduced from 1 mg/L to less than 0.05 mg/L in five village locations. As part of this work, analytical test kits for field use were developed and have been demonstrated to the Department of Public Health Engineering in Bangladesh.
The mechanics of expanding this process to full scale are currently being investigated in anticipation of further test work at water treatment plants throughout the western United States and in Australia.
Published: 22/11/2000