An Innovative Low-Cost Pipe for In-Situ Mining Projects

In-Situ Leaching (ISL) also called Solution Leaching (SL) shown here is a relatively new and increasingly applied method of mineral recovery, which costs less and has a smaller environmental impact in appropriate hydrogeological circumstances compared with other methods of recovery. The technique was initially developed for uranium mines but is now gaining popularity in other fields such as copper and potash mines.

In-Situ Leaching Mining Process

ISL extraction is conducted by injecting suitable chemical leach solutions (lixiviants) into the ore zone below the water table; oxidizing, complexing and mobilizing the uranium or copper; recovering the pregnant (loaded) solutions through production wells (extraction wells or recovery wells); and, finally, pumping the uranium or copper bearing solution to the surface for further processing. The SL technology can only be used for mineral deposits located in an aquifer in permeable rock that is confined by non-permeable rock formations. AS of 2017, two copper mines in Arizona are also starting to utilize this technology. These include the Excelsior Mining Corp's Gunnison Mine located 65 miles east of Tucson, AZ and another site in Florence, AZ.

These two videos provided by Excelsior Mining describe the process of In-Situ Mining in more detail:

The wells on these sites are typically drilled on a 50-ft (15-m) grid and can be about 1000 ft (300 m) deep. Each well must be lined with a pipe that is typically 6-8 inch (150-200 mm) in diamter. The current practice is to use pipe segments that are about 50 feet (15 m) long. These segments are coupled together as they are lowered into the well. There are several shortcomings with the current technique:

  • The pipes are very heavy and handling of them requires special equipment
  • The ordering, manufacturing and shipping of pipe segments to the project site adds time and expense to the project
  • The outside diamter of the pipes is not uniform and is larger near the joints; this reauires larger bore diamter and larger volume of grout to fill the annular space between the well and the pipe
  • Each joint is a potential source of leaking for the chemicals that could contaminate the nearby water sources
  • The use of uniform pipe segments along the entire well depth results in a lower factor of safety at the bottom of the well and a much higher factor of safety near the top of the well

The InfinitPipe® Approach

Onsite-Continuous-Manufacturing of InfinitPipe for Solution Leaching The patent-pending InfinitPipe® solution is to install a manufacturing unit similar to the one shown in this skecth directly on top of the well. Various layers of resin-saturated carbon or glass fabric and core material will be wrapped around the mandrel. Our special resin is fully cured within 3 minutes. So, if a 20 ft (6m) long mandrel is used, in nearly 5 minutes the mandrel can be wrapped and the materials will be cured. This results in a pipe production rate of roughly 4 ft (1.2 m) per minute. So, a 1000 ft (300 m) well can be lined with a joint-less continuous pipe in less than 5 hours!

A further advantage of InfinitPipe® is that as the pipe is being manufactured, the number of layers of carbon or glass fabric benig wrapped around the mandrel can be easily adjusted. This allows us to build a strong pipe based on the maximum pressure at the bottom of the well, and as the loads on the pipe are reduced toward the ground elevation, the number of layers will similarly be reduced. This technique results in a very efficient pipe that has a uniform factor of safety along its entire length -- eliminating unnecessary waste of resources.

The low-cost solution is possible thanks to the on-site manufactured InfinitPipe®, first introduced by Prof. Mo Ehsani in 2012 after several years of development by his infrastructure renewal and repair company, QuakeWrap, Inc. InfinitPipe® received the 2016 American Society of Civil Engineers (ASCE) Innovation Award as the world’s first green and sustainable pipe. Funding for this development has been provided through Small Business Innovation Research (SBIR) Grants from the U.S. National Science Foundation and the U.S. Department of Agriculture.

Some of the advantages of the patent-pending InfinitPipe® solution are:

  • The pipes can be built onsite within a few days of placement of order
  • No advanced ordering and storing of pipes on site is needed
  • The pipe weighs a fraction of conventional pipes and is much lighter and easier to handle.
  • InfinitPipe® has a uniform outside diamter that results in a smaller bore diamter and less volume of grout to fill the annular space
  • The elimination of joints in the pipe results in a much safer solution and significantly reduces the possibility of leaking
  • The pipe design can be adjusted along its height, resulting in a uniform factor of safety along the full length of the well and a much more economical solution
  • InfinitPipe® can significantly reduce the cost of pipelines on ISL or SL projects

Here are some reports and news stories about in-situ mining:

Gold mine of potash sits beneath Michigan, could be worth $65 billion Detroit Free Press, March 16, 2018.

What is potash and why does Michigan have so much of it? Detroit Free Press, March 16, 2018.

Taseko Mines Limited: Technical Report on Florence Copper Project in Florence, AZ, 2017.

In Situ Leach Mining (ISL) World Nuclear Association World Nuclear Association, 2017.

In Situ Leach Uranium Mining: An Overview of Operations IAEA Nuclear Energy Series No. NF-T-1.4, 2016.

Technical Report and Resource Estimate for the Van Dyke Copper Project in Miama, AZ, 2015.

Well-Field Mechanics for In-Situ Mining Shao-Chih (Ted) Way, 2013.

Australia In Situ Recovery Uranium Mining Best Practice Guide 2010.