Cobalt-rich iron-manganese crusts occur throughout the global ocean on seamounts, ridges and plateaux where currents have kept millions of years scouring the rock, so there is no deposit. These cobalt-rich ferromanganese shells are deposited from the surrounding icy seawater onto the rock bottom to form a paving layer up to 250 mm thick. Crusts are important primarily because it may be the source of cobalt, as well as other metal containing titanium, cerium, nickel, platinum, manganese, thallium, tellurium, tungsten, bismuth, and zirconium metal. The cobalt-rich ferromanganese shell is formed at a water depth of 400 to 4,000 meters, and the thickest and most cobalt-bearing ore shell is formed at a water depth of 800 to 2,500 meters. The distribution and thickness of the crust are affected by gravity processes such as landslides, outer layers of sediments, underwater and surface reefs, and water currents.
The ore shell is generated on a variety of bottom rocks, so it is difficult to distinguish the shell and the bottom layer with remote sensing data, and remote sensing data is an important aspect of developing exploration technology. Fortunately, the gamma radiation of the shell is much higher, so the two can be distinguished accordingly. The physical characteristics of the shell include high average porosity (60%), an average surface area of ​​300 square meters per gram, and a very slow growth rate (1 to 6 mm per million years). These features help to draw large amounts of economically valuable metals from the sea to the surface of the shell.
Crusts consists vernadite (manganese oxide) and feroxyhyte (iron oxide), thick crusts amount of fluoroethylene carbonate apatite (CFA), most crusts contain a small amount of quartz and feldspar. The elements normally absorbed by hydrated soft iron ore include cobalt, nickel, zinc and antimony ; iron oxides absorb copper , lead , titanium, molybdenum , arsenic , vanadium , tungsten, zirconium, hafnium and tantalum.
The bulk of the shell has a cobalt content of up to 1.7%, a nickel content of up to 1.1%, and a platinum content of up to one-thousandth of a million points. In the case of large marine waters, the average cobalt content of the crust is 0.5% to 1%, so the crust becomes the most abundant potential cobalt ore outside the land and coast. At the edge of the continent and near the volcanic arc of the western Pacific, the contents of cobalt, nickel, titanium and platinum in the crust are reduced, while the content of silicon and aluminum is increased. The deeper the water at the crust formation, the less hydrated soft iron ore related elements, and the increase in iron and copper. The high concentration of cobalt, ruthenium, osmium, titanium, lead, bismuth and platinum in the shell is higher than other metals because these metals are oxidized to form relatively stable and less active compounds. Rare earth elements typically range from 0.1% to 0.3%, along with other water-forming elements, cobalt, manganese, nickel, and the like, all from seawater. Bismuth is a rare earth element with high concentration in the ore shell and important economic potential.
The seamounts and ridges on which the crust grows impede the flow of ocean waters, creating many streams of water emanating from the seamounts, which are generally more energetic than those of the seamounts. At the outer edge of the peak of the seamount, these water flows have the strongest effect, and the ore shell is the thickest. This unique water flow of the seamount also enhances vortex mixing, causing upwelling, thereby enhancing the primary generation rate. These physical processes have an impact on the seamount biomes, while different seamounts have different biomes. The characteristics of the seamount community are that in the thickest and high cobalt content, the density is relatively low and the difference is relatively small. The determinants of seamount community composition are: water flow pattern, topography, bottom sediment and rock shape and coverage. The size and extent of the seamount size, water depth and minimum oxygen zone. Existing knowledge is not enough to prepare a document on environmental impacts, and a better understanding of seamount ecosystems and communities is needed.
About 40 research tours have been devoted to the study of cobalt-rich crusts, and research has been carried out mainly by Germany, Japan, the United States, the Republic of Korea, the Russian Federation, China and France. The estimated 40 surveys did not include some investigations by the Soviet Union (later by the Russian Federation) and China that the author did not know. However, from the time of about 42 inspections from 1981 to 2001, the cost of each research vessel and field research is estimated to be approximately $32 million, and the cost of onshore research is estimated to be approximately $42 million. $74 million.
The research and development of the mining technology of the shell has just started. Details of the distribution of the crust are still lacking, and there is no comprehensive understanding of the small seamount terrain, but these are indispensable for the development of the most appropriate mining strategy. Field exploration operations usually draw seawater depth maps, derived backscatter and bevel maps, and compile seismic profiles to select sampling points. During the inspection, 15 to 20 cores were sampled and extracted from each seamount. Subsequently, a camera was used to determine the shell and rock and sediment type and distribution, and if possible, the shell thickness. Because there are many beacons at the bottom, large towing equipment is required, and there are many samples collected, so these exploration activities require large, well-equipped research vessels. In the advanced stage of exploration, it is proposed to use deep-water towing side scanning sonar, including broadband sounding technology, and to use the line-connected remote control vehicle to draw and mark a small range of terrain. The dredging sampling can be used, the core is extracted, the remote control vehicle is used for surveying, and the sediment is widely sampled by means of a short-sampling method. Gamma radiometry will determine the shell thickness and determine the presence or absence of a shell under the thin deposit. To understand the seamount environment, you need to use a flow meter mooring device that requires biological sampling and inspection.
The mining and mining guidelines for the 12 mineral shells that have been developed are as follows:
I. "Regional" guidelines:
(1) Large volcanic bodies shallower than 1000 to 1500 meters;
(2) Volcanic bodies of more than 20 million years;
(3) The volcanic structure without large atolls or reefs at the top;
(4) areas where the bottom water flow is strong and continuous;
(5) Developing a perfect shallow sea oxygen minimum zone;
(6) Areas not affected by a large number of river erosion debris and aeolian debris.
Second, the fixed point criteria:
(7) Flat and small terrain;
(8) Peak flat top, peak ridge line low point and ramp;
(9) Slope stability;
(10) There is no local volcanic activity;
(11) The average cobalt content is ≥0.8%;
(12) The average thickness of the shell is ≥ 40 mm.
Technically, shell mining is more difficult than manganese tube mining. The reason why manganese nodules are mined is relatively easy because the manganese nodules are soft deposits, and the ore shells are tightly or loosely connected to the base rocks. In order to succeed in mining, the shell must be removed from the base rock because the base rock will greatly reduce the ore grade. There are five possible methods of operation for shell mining: chipping, crushing, lifting, picking and separation. The proposed method of mining the shell is to use a submarine crawler truck that uses a hydraulic pipe lift system and cable to join the surface of the mining vessel. The mining machine propels itself at a speed of about 20 cm per second. In the case of basic mining, the throughput of the material is 1000000t∕y. In this case, a reasonable mining capacity is 80% of the fracture efficiency, and the blending ratio of the base rock in the ore shell is 25%. Some of the innovative new systems proposed for mining shells include: using a water spray to separate the shell from the substrate; on-site filtration techniques; using sound waves to get the shell off the substrate. These suggestions give hope, but they need further study.
The importance of the metals contained in the shell to the world economy is evident in its consumption patterns. The primary use of manganese, cobalt and nickel is in the manufacture of steels which impart properties to steel. Cobalt is also used in the power, communications, aerospace, engine and tool manufacturing industries. Nickel is also used in chemical plants, refineries, electrical appliances and motor vehicles. Cobalt is a by-product of copper mining, so the supply of cobalt is closely related to the demand for copper. The same is true for cockroaches, which are by-products of copper and gold mining. Due to the unstable supply, companies have to seek alternatives to cobalt and antimony. As a result, the market for cobalt and antimony has grown very limited over the past decade, so prices are lower. If other rich sources of these metals are developed, the enthusiasm for reusing the two metals in the product will increase and the market will expand.
It has recently been determined that in addition to manganese, cobalt, nickel, copper and platinum, the shell contains other metals that may make people more actively exploited. For example, the value of titanium is second only to cobalt, the value of niobium is higher than that of nickel, the value of zirconium is comparable to that of nickel, and the value of tantalum is almost twice that of copper. The above analysis assumes that an economically viable metallurgical refining method can be studied for each metal.
Depending on the grade, gross tonnage and ocean conditions, the core equatorial mining potential is greatest in the Central Equatorial Pacific region, particularly in the international waters of the Johnston Island Exclusive Economic Zone (USA), the Marshall Islands and the Central Pacific Mountains, but French Polynesia, Kiribati and The exclusive economic zone of the Federated States of Micronesia should also be considered.
Many of the metals found in the shell are critical to maintaining the efficiency of modern industrial societies and improving living standards in the 21st century. It is increasingly recognized that cobalt-rich shells are an important potential resource. Therefore, information gaps on all aspects of mine shell mining need to be filled through research, exploration and technology development.
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