The construction of a water treatment plant using ChemSulphide® technology at the Wellington Oro Mine site has been reported in earlier papers (Bratty et al, 2008). The plant is now in operation and actual operating results can be reported.
The Wellington Oro Mine site is a closed silver-zinc mine located near Breckenridge, Colorado, USA. The ChemSulphide® technology was selected from an international call for proposals as the best technology to address metal contaminated water at the Wellington Oro site after a review by the US Environmental Protection Agency (US EPA).
The water treatment plant is successfully treating mine drainage containing cadmium, zinc, and other trace metals, removing dissolved metals to meet strict effluent specifications set by Colorado Water Quality Standards (shown in Table 1).
Table 1: Wellington Oro water chemistry
6.5 to 9.0
< 0.0005 mg/L
< 0.10 mg/L
The ChemSulphide® precipitation process was selected instead of lime treatment for application at the Wellington Oro site because it does not generate a waste sludge that would otherwise require disposal and ongoing monitoring. An equivalent capacity lime plant would have produced an estimated 1.5 million litres of metal-laden sludge annually, leaving an environmental liability and adding to long-term operating costs, as shown in Table 2.
Table 2: Comparison of Design Specifications for Treatment Options
Lime Treatment (at maximum flow and load)
Sulphide Precipitation (at maximum flow and load)
150 USGPM (35 m3/h)
150 USGPM (35 m3/h)
Volume of sludge product
390,000 US gallons/yr (1,500 m3/yr)
Saleable zinc recovered
178,000 pounds /yr (81,000 kg/yr)
Zinc content of output
Potential zinc revenue
Capital cost (estimate)
Estimated annual operating cost
Metal-laden sludge storage cost
Instead, the sulphide precipitation plant produces a saleable zinc-cadmium sulphide product, which can be sold to off-set treatment costs, and recycled into useful products.
In addition to delivering operating cost savings, the capital cost of the sulphide precipitation plant for this site was estimated to be approximately 33% less than a lime plant with equivalent capacity.
Dexing Case StudyThe ChemSulphide® Process has also been used at Jiangxi Copper’s Dexing copper mine, located near Dexing City in southeastern China, which at 120,000 tonnes of copper per year is the largest open pit copper mine in China. The water treatment plant at Dexing operates at a maximum flow of 1,000 m3/h and treats surface water run-off and drainage from waste dumps and the low grade stockpile. In this application of ChemSulphide®, it is being used for copper precipitation and recovery upstream of an HDS lime plant. This configuration results in a number of benefits versus using only a conventional HDS lime plant, some of which are summarised in Table 3.
Table 3: Benefits achieved by ChemSulphide® at Dexing Mine
Benefit vs. Lime Treatment Alone
580 tonnes per year
Lime use reduction
1,240 tonnes per year
Reduction in lime sludge produced
6,000 m3 per year
From a short term perspective, the revenue generated from the recovered copper supplemented by the savings in lime consumption mean that instead of being a cost, Dexing’s water treatment facility generates a profit for the mine. In the longer term, the copper removed in the ChemSulphide® plant is copper that won’t report to the lime plant sludge, and as a result the long term liability to the mine due to the storage of the lime plant sludge is considerably reduced. Of course, the reduction in metals reporting to the lime plant also reduces the quantity of sludge produced, resulting in a smaller requirement for storage of sludge and reduces the associated construction and monitoring costs for storage.