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Mineral Processing:
A Breath of Fresh Air

People working Mining Processing

Mine sites could be missing out by ignoring oxygen management during the gold leaching process.

Air Liquide is a company that would rather not be pigeon holed when it comes to metallurgy.

Established in France in 1902, the company has grown into one of the world’s largest industrial gas suppliers over the past century, earning a spot on the coveted Fortune Global 500 list.

Air Liquide is a major supplier to the Australian mining industry, notably for its minerals processing solutions in areas such as flotation and pH control, oxide roasting, gold and in-situ uranium leaching, process water treatment and nitrogen inerting systems for longwall underground mines.

The company is known for its gold leaching services, providing a customisable leaching solution to mine sites by determining the oxygen needs of gold ores and concentrates during the hydrometallurgical process. This process helps the company provide a customisable solution that leads to significant production gains.

Air Liquide engineers evaluate the mass transfer coefficient and reagent consumption levels to help pinpoint required oxygen levels in the pulp. Formerly, Air Liquide served solely in the capacity as a gas supplier for this process, but it has in recent years made the move towards equipment supply and postinstallation support to cement its status as a turnkey provider of gold leaching services.

“What we’re pushing towards is actually providing the injection technology equipment as part of our package as a full turnkey solution. We’re stepping away from the years of just selling gas molecules and are now selling a gas solution,” Air Liquide Australia’s mining specialist Rick Edwards says.

“We’re also in a beautiful position where we can stay neutral, so we can look at many different types of injection technology and decide what is best for that particular site based on their mineralogy, geography, or a number of other factors.” Edwards argues that it is easy for onsite maintenance staff in charge of leaching operations to overlook the potential detrimental effect of improper oxygen system management in the leaching process. “Any issues with the oxygen system can be difficult to identify as it has no direct effect on the ongoing running of the plant,” he says.

Despite this, injection is essential for the oxidation of labile iron sulphides in the leaching solution, and correct oxygen management can help workers achieve maximum gold recovery while also increasing passivation of cyanide consumers, which has the added bonus of reducing total cyanide consumption.

Air Liquide also reduces water discharge in the process by eliminating cyanide compounds with ozone or restoring pH levels with carbon dioxide, which allows plants to recycle water and thus reduce water discharge. The company’s solution also eschews chlorine and, in turn, the ore roasting process that precedes it, which can result in the emission of large quantities of sulphur dioxide. This combination of factors results in a leaching process that maximises returns while also being better for the environment.

Edwards notes that there is not only a trend towards more environmentally benign leaching solutions in the gold sector, but also towards fresh ore treatments as mines go ever deeper. “As people continue to dig deeper and do feasibility studies that aren’t just for a five-year mine run — with our clients we’re often looking at 10 years at least — that means that we’ve got to go deeper and treat more combinations of ore,” Edwards explains.

“There’s definitely a trend that gold mines across Australia are starting to treat a lot more fresh ore than before and as such that definitely puts a bigger emphasis on proper oxygen requirements when compared with the past.”

Gold mine processing

That means sites could be able to treat larger batches of ore in difficult areas while still meeting their margins, as well as sites looking to extend their mine life.

Air Liquide encourages sites to approach them early on in the procurement process to facilitate the best approach. Due to the company’s neutral approach to technology, it doesn’t favour one brand over another, instead looking at equipment combinations that will provide the optimum solution.

This combination of tech neutrality and lab testing — including gas chromatography services — makes the company more than just a gas supplier, according to Edwards.

“If our rivals are people who are just selling one piece of equipment, they are going to claim that it is the best for a particular mine site, whereas we would look at their piece of equipment amongst others and then conduct tests to work out which is better,” Edwards explains. “In that regard, we’re always going to have a much better case study and be able to research a multitude of options.”

In keeping with this appeal to current demands for technology driven solutions, Air Liquide has rolled out a wireless condition monitoring solution for dissolved oxygen and pH levels. The Air Liquide wireless monitoring system is designed primarily for gold and copper leaching monitoring. Using this system, up to 255 monitors can be connected wirelessly to a main controller at a safe distance of up to four kilometres away.

It is part of the company’s recently established umbrella brand Nexelia, which combines Air Liquide’s processing solutions into a cohesive whole. It is the latest example of the company’s tailored approach to technology.

“This is really new. The first package has just been ordered for Australia following development in South Africa. We’re very excited about how it could help mine sites maximise their potential during leaching,” Edwards concludes.


 about Mining or Air Liquide presenting and exhibiting at ALTA 2019

This article can be found in the April 2019 edition of Australian Mining

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