Wealth from Waste

Mining has long been an active part of Arizona’s history and makeup because of the State’s topography and its wealth of minerals. The Town of Bisbee, in particular, is one of the most historic mining sites in North America.

Located about 50 miles south of Tucson and just 25 miles down the road from the popular tourist town of Tombstone, Bisbee was founded in 1881 and quickly became known as the “copper capital” of the Wild West because of its vast and obvious reserves of copper ore. The miners, too, added colour and excitement to the town.

Today, almost 130 years later, some of that valuable copper still remains and is clearly visible from a roadside ‘lookout’ into one of the original pits.

The open pit, in fact, almost rivals the attractions of nearby Tombstone in popularity with history buffs looking for a piece of the past.

Active mining stopped at the site in 1975 by then owners Phelps Dodge, and it has been dormant to mining for almost three decades except for the maintenance of an office which oversees reclamation and remediation projects.

In 2003, the Bisbee site was selected by Phelps Dodge (now Freeport-McMoRan Copper & Gold Inc.) as a demonstration site to apply a unique new sulphide precipitation technology developed by Vancouver-based BioteQ Environmental Technologies Inc. The mining giant recognized the importance of investing in technologies that could enhance water management and deliver environmental benefits while maximizing resource recovery. The goal of the project was to recover dissolved copper from drainage emanating from a stockpile of low grade ore, and gradually reduce the copper in the stockpile so that the site could eventually be reclaimed.

The copper-enriched drainage is the result of Mother Nature. When it rains or snows in Bisbee, water leaches through the stockpile and combines with natural oxidation reactions within the pile. As a result, the drainage contains dissolved copper and iron in acidic water.

Through an eventual 50-50 joint venture called Copreco LLC, BioteQ and Freeport-McMoRan set out to build a US$3.2 million process water plant at the Copper Queen Mine site.

The plant (adjacent photo) has a capacity to process 500 m3/hour of water and recover up to 1.8 million pounds of copper annually.

The plant presently treats over 2 billion litres of water annually, with process availability of 98%, and is operated using procedures that meet strict environmental and safety requirements. Site safety is of prime importance to both Freeport-McMoRan and BioteQ, and the plant has a perfect safety record, with no time lost for safety incidents, a fact that has been recognized by the US Department of Labour -Mine Safety and Health Administration.

Teryl Murray, BioteQ’s Regional Operations Manager, USA and Mexico, says: “Technically, the plant applies BioteQ’s patented BioSulphide Process, which uses biogenically produced hydrogen sulphide gas to selectively precipitate dissolved copper from water draining from the stockpile. The system’s bioreactor can produce up to 3.8 tonnes/day of hydrogen sulphide gas on site. By producing H₂S “on demand”, the plant can minimize the inventory of this potentially harmful gas on site, which enhances site safety.

“Two separate stages of processing are involved in the system; biological and chemical.

“In the biological stage, sulphur-reducing bacteria contained in an anaerobic bioreactor produce hydrogen sulphide gas. The bioreactor is isolated from the water treat- ment tanks, creating a controlled environment that produces H₂S gas. The gas is transferred to a “contactor tank” that contains the water to be treated.”

“In the chemical stage, the solution chemistry in the “contactor tank” is adjusted to selectively precipitate dissolved copper as solid particles of pure copper sulphide. The precipitated metals and treated water are pumped to a clarifier tank where the water is separated from the metal solids. The treated water is pumped back to the stockpile. The solid copper sulphide is shipped to a smelter and converted into products.”

Teryl Murray explains: “The BioSulphide Process can be used instead of a conventional “lime treatment” plant. In lime treatment, Ca (OH)₂ is added to the metal-laden water. The dissolved metals precipitate into solids, forming a metal- laden sludge. The disadvantage of the lime treatment is that the metals cannot be recovered, and the resulting sludge must be carefully stored and monitored to prevent the metals from re-dissolving and re-entering the environment, thus creating a long-term environmental liability that must be managed.”

At the Copper Queen site, the BioSulphide process delivers both environmental and economic benefits. First, the process can selectively remove more than 99% of the dissolved copper from the water, producing a high-grade (30+ %) saleable copper sulphide product suitable for refining, and treated water that is recycled back into the stockpile to recover more copper. Second, because the copper concentrate can be sold, it generates a profit for the joint venture partners, providing a source of funds that can be used to offset eventual site remediation costs.

The Copreco plant is meeting the original goals of the project set out in 2003. For Freeport-McMoRan, the plant maximizes resource recovery while delivering environmental benefits; for BioteQ, the plant has served as a proving ground that has enabled the company to expand the application of its technologies to 10 sites with leading mining firms around the globe. BioteQ is now working with Freeport-McMoRan at another site in the US to apply a new water treatment technology -this time to remove sulphate from water.

The recovery system used by Copreco at the Copper Queen Mine not only demonstrates how wealth can come from waste, it also shows how cross-border companies can work together to achieve resource recovery, while improving overall environmental performance.

And that benefits all!