History of Mining Technologies for Nodules and Other Mineral Deposits
Over forty years ago, they started to develop technologies for mining of nodules from the World Ocean bed. But the deep-sea deposits development is a rather specific sector with its own peculiarities. The major complexity consists in the fact that mineral deposits are located very deeply (up to 8,000 meters). That is why the known mining methods, such as a dredge method for the depth of 100 meters, cannot be applied due to high pressure and load on materials which a mining apparatus can be made from, as well as adverse climatic conditions (hurricanes, storms, underflows, etc.). In order to mine the nodules people need innovative technologies that will allow overcoming all the complexities connected with the extraction of minerals from the ocean bed.
In general, there are dredge, hydraulic, bucket, near-bottom and combined methods for the development of off-shore deposits of solid mineral resources. By present time, they have developed and field-tested three methods for the extraction of nodules from the ocean bottom: the hydraulic, rope and shuttle types.
Hydraulic dredge hoppers and hydraulic dredgers are widely used for undersea mining operations. Depending on the type of the applied equipment, there are suction-type, air-lift and ejection dredgers. This type of equipment has a suction pipeline instead of a chain-and-bucket line. The pipeline is fixed on the frame or hung with the help of rope facilities and then lowered/raised from the base vessel using hoisting devices: winches, telphers, cranes, barrels, etc. A technology for the development of underwater solid mineral deposits is analogous to the dredge method.
The first testing of nodules collection systems according to the hydraulic method was started in 1970 at the Florida coast in the Atlantic Ocean at the depth of 1,000 meters. The testing was carried out by Deep Sea Ventures using a specially equipped cargo vessel called the Deep Sea Miner. Nodules were collected with the help of a pneumatic system and conveyed up to the vessel of 6,750 tons displacement, equipped with a 25-meter derrick-crane and a central 6x9 m tank.
In late 1970s, three American consortiums conducted a series of tests using hydraulic mining systems. They collected nodules using a dredge and conveyed them to the rising pipe base that hung up under the vessel.
Ocean Management, Inc. used a dynamic positioning drillship called Setco-475. They tested two lifting systems: centrifugal axial-flow pumps at the maximum depth of 1,000 meters and air injection under pressure at the depth of 1,500 and 2,500 meters (pneumatic lifting). Two collecting devices were trailed behind the pipe: an ejection suction dredge and a mechanical collector with a reverse conveyor. In the course of that experiment, the first collector was lost as a result of a failed manoeuvre. When three tests were completed, they collected about 600 tons of nodules. These operations were carried out at a distance of 1,250 kilometers south of Hawaiian Islands.
In 1976, Ocean Mining Associates re-equipped an ore-carrier of 20,000 tons’ displacement that had a hatch in its body for the drilling equipment installation, derrick-crane and a bow thrust unit. Nodules were collected with the help of a suction dredge towed by the ship, and the nodules were conveyed up using a pneumatic system. The testing was suspended as the electrical connections along the pipeline appeared to be not quite waterproof.
At the beginning of 1978, two more series of testing faced new challenges when a suction dredge was stuck in bottom sediments, and a storm started. In October 1978, they lifted 550 tons of nodules within 18 hours at a maximum capacity of 50 tons per hour. The testing was suspended due to a pump blade breakdown.
In 1978, Ocean Minerals Company (OMCo) leased from the US Naval Forces a ship called Glomar Explorer. That was a 180-meter long dynamic positioning ship of 33,000 tons’ displacement. It was equipped with a complex system for deployment of pipelines and an electric connection network. OMCo designed a self-drive collector equipped with Archimedes propellers to help it move over a soft sediment layer of the ocean bottom. After these first experiments at the depth of 1,800 meters near the Californian coast, the tests were ceased as it was impossible to open the hatch in the ship body. In February 1979, the experiment was terminated but the researchers collected a great amount of data necessary for further development and experiments.
In 1988, a French company Genomod designed a system consisting of a half-diving surface double-hulled platform, a 4,800 meter hard steel pipeline and a flexible 600-meter long hose with an internal diameter of 38 cm that connected the pipeline with the seabed dredge. A self-propelled dredge was a 330-ton suction dredge of 18 m long, 15 m wide, 5 m high, with 78-ton buoyancy. The research team planned that it would move over the bottom and collect nodules, prepare them for pumping through a flexible hose into an interim tank, and finally – to the base ship.
India is now developing a mining vessel and has completed some testing of a prototype at the depth of 410 meters. In future, they plan to test it at the depth of 6,000 meters. A 3-meter wide apparatus will move over the seabed using its plastic crawler belt, and the collector installed at the front of the apparatus will, while vibrating, push the nodules to a grinding area, from which the nodules will be pumped out to the vessel through a 10-cm hose.
Since 2006, a Canadian company Nautilus Minerals has been carrying out its operations on the development of a sulphide deposit called “Solar-1” at the depth of 1,600 meters. It has designed a mining apparatus and is now constructing its invention, but the commencement of mining operations is postponed every now and then due to a number of difficulties.
Lockheed Martin has been also designing and developing its mining apparatus since 1970. In 2013, it obtained another license for exploration in the Clarion-Clipperton Zone, and now continues its experiments with its own mining apparatus.
In 1972, a syndicate of 30 companies tested a technology of a continuous chain-and-bucket conveyor with an 8-km long rope. This conveyor was equipped with evenly placed buckets that were launched at the ship’s head and returned to the ship’s back. They were able to collect some nodules, but in the course of the experiment the conveyor cable got tangled and the testing was ceased.
As a result of some difficulties caused by relief obstacles on the seabed (rock blocks, benches and potholes), the French engineers elaborated a concept of a free-moving shuttle mining system consisting of a number of autonomous vehicles each of which independently would submerse down to the ocean bottom. Having approached the bottom, they would unload its ballast, take up a strictly determined position and start to collect nodules. Then, using lead accumulators as a source of energy, they would move using the crawler belt and adjust its weight with the help of ballast.
The intention was that after loading of 250 tons of nodules these shuttles would unload their extra ballast and each start its independent surfacing. After surfacing, they would be towed to a port to unload the collected minerals. However, upon completion of technical and economic studies, it turned out that the materials used for the structure were unable to maintain the apparatus buoyancy.
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