Editorial Feature

The Development of Underwater Mining

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A submersible developed in 1964 by the U.S. Navy called Alvin was one of the first of its kind with the ability to go to a depth of 14,800 feet for up to 10 hours. More recently Director James Cameron received much publicity for a submersible he helped to build called the Deepsea Challenger that went down the Mariana Trench at a depth of 10.9 kilometers.

Some of what drives divers are sheer curiosity, but often there is a desire for rare earth elements. Broadly defined remote operated vehicles, or ROVs, operate either through continuous line bucket systems (CLB) or hydraulic suction systems for sample collection. In the bucket system, a conveyor belt pulls up gunk; in the hydraulic suction system one pipe pulls mud up and another transfers it back down.

For example, the Woods Hole Oceanographic Institution built, first in 1988 and then again in 2002, a certain modern version of a bucket system ROV in “Jason” with a 10-kilometer, or 6-mile electro-optical as well as mechanical tether to an oceanic device. At the surface, staff controls its equipment including sonar and video imaging, electronic cameras, lighting, and precision navigation equipment. Manipulator arms collect samples and, to help them, an elevator platform carries larger items upwards.

The average Jason dive lasts one to two days, although operators have kept it down for as long as seven days, especially in several locations with hydrothermal vents within the Indian, Atlantic and Pacific Oceans where the earth’s magma heats seawater so that precious minerals leach out of rock and then solidify with colder incoming water flows.

With ocean technology becoming more commonplace, understandably, people seek to usurp what they can, for example, the Canadian company called Nautilus Minerals. The Papua New Guinean government granted it a 20-year lease to mine offshore for up to one mile beneath the surface for high-grade copper, gold, zinc, and silver. Similarly, the Indian government is spending money to mine nickel, copper, cobalt in the Central Indian Basin and to build a rare earth mineral processing plant and an exploration ship.

Countries thus regulate some of the mining. Also, international groups exist with the International Seabed Authority being a regulator of the sea floor across international waters.

Nautilus Minerals plan to harvest seafloor sulfide deposits in 2018, but it still does not yet have production-scale mining systems that can bring thousands of tons of rock from 15,000 feet below the water to the top.

What it does have to date is equipment weighing, in tons, about 220 to 340 and operates at depths up to 1,600 meters. Designed as a hybrid of trenching equipment and continuous mining equipment, the result is about 50 feet in length and 15-20 feet in width. Remotely controlled from the ship with the ship connected to a central pumping system one cutter can work on the seafloor to make it level enough for grabbing by a bulk cutter that then grinds it. A collecting robotic machine uses pumps to move seawater slurry through a pipe to a Riser and Lifting System (RALS). The RALS comprises of a large pump and rigid riser pipe supported from the vessel that delivers the slurry to the surface. The pump is supported on a solid vertical pipe suspended beneath the support vessel.

These machines cut material in temporary positions on the seafloor for collection by the third machine, the collecting machine, that also has a large robotic vehicle, to cut and collect material.

On the deck of the production support vessel, the slurry is dewatered and stored temporarily in the vessel’s hull and the particles, once filtered out, are then discharged to a transportation vessel moored alongside. Filtered seawater is pumped back to the seafloor through riser pipes, a process that provides hydraulic power to operate the RALS pump.

Overseeing some of the pieces submerged is a launch and recovery system, contracted out to GE Oil and Gas, that is made up of electric and hydraulic power units.

Nautilus expects profitability when it can mine two million tons of rock every year.

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