Fractal theory is used to study the granularity distribution law of the broken cobalt-rich crust collected by spiral cutting. The result shows that its granularity distribution has a very good fractal structure and can be quantitatively described with fractal dimension. Through a large number of experiments, it is preliminarily determined that the fractal dimension of the granularity distribution of broken cobalt crust and its simulation material is between 2.4236–2.6112. A regression model for the relationship between the cutting depth and granularity distribution is proposed to predict the cutting result of cobalt-rich crust and improve the design of deep seabed mining system.
Cobalt crust, which grows on smooth seamount slope from 500 to 3000 meters depth (Yamazaki and Sharma, 2000), is multi-metal ore that is rich in cobalt, nickel, silver, copper, gold, platinum, and rare-earth element, and now is a emphasis of researching on deep sea mineral resources in the home and foreign (Manheim, 1986; Glasby, 2002). Because of the complicated environment of deep-sea mining, cobalt crust cut and broken by mining head should be lifted to the supporting ship by the collection and lift system (Chung, 1994; Liang, Shi, and Cui, 2002). Undersized granularity will pollute seabed environment seriously, yet oversized one will block the collector and lift system, so the granularity should be controlled strictly in the required range: The maximum diameter of broken crust is required to be less than 50 mm. Fractal theory being used to study granularity distribution law of cobalt crust to ascertain the situation of broken cobalt crust has signification to the research of deep-sea mining system.
Fractal is an abstract description to the phenomena of objective world that is not smooth, continuous but not differential, fragmental.