Getting the lixiviant to all parts of the heap leach pad is a common operational problem. But if you can get lixiviant of the right temperature to all parts of the heap leach pad, the payback can be great.

First consider how you heat the chemical-laden water that is probably highly corrosive so that you can pump it into the selected part of the pad. One approach that hit my desk just today is to use the SubCom technology.

SubCom is short for Submerged Combustion. Here is how it works:

The process is a highly energy-efficient method of heating large quantities of liquids often dirty or corrosive—by forcing the products of combustion directly through the liquid. Heat transfer occurs between the high temperature (in excess of 2,500 degrees F) gas bubbles as they collapse through the solution so there are no heat transfer surfaces to foul. When the gases are finally allowed to exhaust they exit at the same temperature as the heated solution at atmospheric pressure. With conventional methods the heat exchange is indirect and the products of combustion are wastefully exhausted directly into the atmosphere at considerable temperatures.

The folk who make and sell equipment that uses this remarkable approach are SubCom, and they are right here in Vancouver, BC. The following is a brief account of a case history where they applied their equipment:

In 1994, Compania Minera Cerro Colorado (CMCC) approached Inproheat about utilizing Submerged Combustion to heat raffinate with a pH of 1.2 – 2.0, for their copper heap leaching operation near Iquique, Chile. Inproheat constructed and delivered 10 MM Btu/h SubCom unit for CMCC in 1995.

The CMCC site is situated at 2500m ASL in a remote location. To combat the effects of low seasonal temperatures, the raffinate is heated from 15°C to 35°C before it is sprayed onto the leach pads. The SubCom units are fired with No.2 diesel fuel, with propane used as pilot gas to initiate lighting of the burners. This was the first use of a non-gaseous fuel for SubCom.

Because of the corrosive properties of the process fluid, corrosion test work was undertaken to select suitable materials of construction. For the combustion chambers, Carpenter 20Cb-3 was chosen. The tank, vent stack and piping were fabricated with FRP using Derakane 411-45 resin. The pump and valves are made of CD4NCu alloy.

The SubCom units were supplied mounted on a steel skid, fully wired and piped, including the control panel and control PLC. The system was function tested at Inproheat’s shop with water before being shipped to the CMCC site.

Performance surveys during operation indicated a heating efficiency of 93% based on the diesel fuel higher heating value. After a period of successful operation, a second 10 MM Btu/h SubCom system was constructed and installed in 1996.

The second part of the trick of getting warm fluid to the right part of your heap leach pad is Hydro-Jex. Here is what I wrote about this technology in a now forgotten article:

At the SME Annual Meeting & Exhibit meeting I listened to a paper Hydro-Jex - Heap Leach Pad Stimulation Technology: Ready for World Wide Industrial Adoption? The author and presenter was Thom Seal of Newmont Mining Corporation from Elko, Nevada. He talked with enthusiasm and knowledge of the work he has done to recover more gold from old heap leach pads. My quick summary of his work: in any heap leach pad there are zones where the gold has not been removed, mainly because construction practices prevented access to these zone by the seeping fluids supposed to liberate and transport the gold to collection points. He has devised novel ways to locate these “unprocessed” zones and to get the right chemicals to these zones to get the gold out. With gold at $600 an ounce plus, [I wrote this a year and a half ago] it makes good economic sense to go after these reserves, and he has proven you can do it.

To read his paper, you will need the meeting CD, or you may want to contact him at thom.seal@newmont.com and get a copy of his paper or PowerPoint presentation. To whet your appetite, here is the abstract of his paper:

The Hydro-Jex technology has been used by Newmont Mining Corp. on the gold heap leach pads on the Carlin Trend - Nevada for three years to recover the inventory gold and change the chemistry in the pads. This research and development patented process is described and the data presented. Information on drill sampling, geophysical surveying, followed by leach pad stimulation with impacts on solution chemistry and gold recovery are discussed. Can this technology be used to rinse and close heap leach pads faster with reduced pump energy cost and improved recovery?

I believe the answer is yes and I can only encourage you to take a look at his data to convince yourself.

Thom earned his Ph.D. for the work he has done in developing the Hydro-Jex technology. I suspect this is a well deserved degree. I chatted briefly with him after his presentation and he told me he is refining the work for future publication in the SME magazine. He speculated on the potential application of his methods to copper heap leach pads. Seems there is another world of opportunity awaiting this development.

Key to implementing the method is locating the dry zones in the heap leach pad. I stopped a while at the hydroGEOPHYSICS, Inc, booth. They have the technology and will be working with Thom and Newmont on future application of the technology. They have promised to keep us informed so stay tuned, or better still contact them and try the process on your heap leach pad.

Thus bring together hydroGEOPHYSICS, Hydro-Jex, and SubCom and you have more than a mouth-full; you may have more gold, now headed over $1,000 an once.