Understanding the Effects of Deep-Sea Conditions on Seafloor Massive Sulfide Deposits Crushing Process

ABSTRACT Seafloor massive sulfide deposits provide a rich polymetaliferous ore including elements such as gold, silver, copper, etc. They can be found in oceanic volcanic zones at the seafloor. The challenge is to extract this ore and raise it to the surface. The most promising technique consists of the following steps:Extracting the ore from the seafloorReduce the extracted ore down to sizes small enough for raising to the surface (crushing)Raising the crushed material to the surface. Size reduction of the rocks by mechanical methods in atmospheric conditions is well understood. However, the effect of deep sea hydrostatic pressure on the mechanical rock crushing process is largely unknown, but will be critical for future subsea mining operations. This paper describes a series of tests performed by Technip to observe and understand the effects of deep-sea conditions on rock crushing. A compact rock crushing unit, including a MMD 200 series sizer, was installed inside a large hyperbaric chamber. Tests were performed in atmospheric conditions and at several hydrostatic pressures up to 200 bar, in a highly controlled manner. The crushing process was video observed, crushing forces were measured in real-time, and resulting particle size distributions were analysed. Three different rock types with geotechnical properties relatively similar to massive sulfides deposits were processed namely, puzzolane, limestone and a formulated concrete. Rocks were water saturated before being tested to reproduce seafloor saturation conditions. The results have clearly settled that deep-sea crushing requires more power than a classical terrestrial crushing. This statement will be critical for the developement of Technip seafloor crushing unit project.