African Oxygen, part of The Linde Group, is using ozone for the cyanide destruction process at gold mines. Ozone is generated on site, by using ozone generators and using oxygen. The ozone was injected using a specially developed contacting system to ensure that optimal reaction efficiency took place before the water was pumped into the tailings dam. Cyanide oxidation occurs quickly, with free
cyanide being reduced by more than 85%. The ozone consumption during the trial was about 2 g of ozone for every gram of cyanide.
The need for cyanide destruction has
increased over the years due to the growing demand for sustainable solutions to neutralize destructive cyanide in tailings dams as more mining companies voluntarily subscribe to the United Nation’s International Cyanide Management Code (ICMC). The fundamental aim of the code is to manage the use of cyanide throughout the gold beneficiation process, which limits the release of solutions containing cyanide into the environment from spillages and tailings disposal. Although compliance with the code is voluntary, it has been implemented by the world’s major gold producers.
The advantages of using the ozone-based process for cyanide destruction should, however, be a huge driver for mines when considering a cyanide destruction process.
The advantages associated with using this system include the fact that no adjustment to the tailings stream is required when installing ozone equipment and the reaction is rapid, complete, irreversible and by-product free.
Global Water Intelligence has recently published a study on the water treatment market. The report noted strong growth in ozonation and advanced oxidation water treatment applications. The growth drivers are the need for higher quality water while raw water quality is decreasing, the use of wastewater for applications previously supplied by potable water, and the investment in sludge management.
Global growth for ozonation is expected to grow at nearly 10% annually over the next 6-7 years from a base of about $360 MM. Advanced oxidation is expected grow at over 30% annually over the same period albeit from a base of only a $20-30 MM.
Iron (Fe) and manganese (Mn) are often found in groundwater. High levels can create aesthetic issues with drinking water including taste and odor problems as well as staining of water fixtures. A common method of removing these contaminants is to oxidize them and then remove the precipitates via filtration. Ozone is one of the oxidants employed in this application.
To measure the oxidation process, Oxidation-Reduction Potential measurements are taken using ORP sensors instead of direct measurement of the ozone residual. Hach Company (Loveland, CO), is developing a technique of measuring ozone in the Fe/Mn application using differential turbidity measurements, i.e. the amount fo turbidity before and after ozonation. This method take advantage of the formation of the Fe/Mn precipitates after oxidation to measure the amount of ozone present. The amount of precipitate formed should be proportional to the ozone in solution.
Hach’s research reported in Ozone Science and Engineering July-August 2010 shows that differential turbidity measurements are indeed proportional to ozone dose. In addition, testing also indicated that differential turbidity had lower maintenance requirements than ORP.