Mining

Process Wastewater

Mining operations are required to treat process water before it is discharged into the surrounding environment. This wastewater may contain many kinds of contaminants, including:

• Cyanide compounds: Cyanide, Cyanate, Thiocyanate

• Nitrogen compounds: NH3, NO2

• Collectors and Flotation Agents: Xanthates, Dithiophosphates

• Metals: Iron, Manganese, Zinc, Copper

Ozone can be used “on demand” to solve multiple water treatment issues safely and efficiently. In the mining industry, it is a highly effective and affordable solution for removing cyanides, nitrogen species, thiol collectors and metals from process water before it is discharged.

Cyanide

Cyanidation is the process of using cyanide to transform gold into a water-soluble form which allows for its extraction and processing. Cyanidation is the most common form of gold extraction. Worldwide, one billion tonnes of ore are processed by cyanidation.

Because cyanide is highly toxic, it must be destroyed in the process water before it is released into the surrounding environment. Ozone is an effective treatment option for cyanide compounds, as they quickly decompose in the oxidation process.

Nitrogen

Ozone will also easily oxidize nitrite to nitrate, and if pH is adjusted, ozone can effectively convert ammonia to nitrate. The dose needed for oxidation of NO2 to NO3 is approximately 3.4 kg O3/1kg NO2, which makes it an economical solution for treatment of nitrites.

Figure 3. Graph showing the effect of pH on oxidation of ammonia to NOx. – COULD ADD A GRAPH HERE FROM THE ORIGINAL DOCUMENT.

Collectors

Sulfide ores are typically treated with froth flotation agents, such as thiol collectors like xanthates, dithiophosphates, and dithiocarbamates. These collectors can cause sulfide minerals to “repel” water and form bubbles. Residual flotation agents or their by-products can affect the chemistry of the mine processes and/or are highly toxic to aquatic ecosystems.

It is therefore necessary to remove or reduce flotation reagents from process water, either to allow for recirculation of the water or for discharging it into the environment. Studies have shown that oxidation with ozone is highly effective at degrading and removing thiol collectors like dithiophosphates and xanthates.

Metals

Regardless of the source of the water, ozone and post-filtration will quickly removed iron, manganese, sulphur, lead, arsenic and other metals from process water.

Other technologies leave gaps in water treatment that can be filled by ozone:

• Chlorine produces multiple types of chemical by-products and is slower than ozone in removing contaminants. It also is dangerous to handle and gives off Greenhouse Gas Emissions (GHG);

• Hydrogen Peroxide does not produce harmful by-products, but it is slow to act on removing contaminants and its effectiveness-to-cost ratio is poor. It also produces GHG and is dangerous to handle.

Mining process water will vary greatly depending on the type of mining operation. Knowing the specific contaminants and their levels in the water helps determine the required ozone demand. Given the critical nature of the industry, wastewater from mining production requires careful system design to ensure safety and efficiency.

Ozone Aclarus engineers assess the treatment needs for each mining operation and design a solution to fit the need through testing and/or pilot demonstrations. This is done to determine the level of treatment and ozone required (e.g. disinfection, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), etc.).