Study on the crushing characteristics of polymetallic nodules based on the single-tooth roller crusher

Pipeline lifting mining systems have strict requirements for the transport particle size of polymetallic nodules, and the mined nodules generally require primary crushing treatment. This paper investigated the nodule crushing characteristics using the single-tooth roller crusher. The mineral composition and microstructure of nodules were investigated by the X-ray diffraction, scanning electron microscopy, and energy-dispersive spectrometers. It was found that the kernel is predominantly composed of silicate minerals while the outer layer is mainly comprised of iron‑manganese oxides and hydroxides. The high porosity structure and low interfacial bonding strength lead to the low tensile strength. Based on slow compression tests and existing research data, the Tavares UFRJ breakage model parameters for nodules were calibrated and validated. Nodule crushing simulations under different initial particle sizes, discharge opening gaps, and rotational speeds were conducted. It was observed that the maximum particle size after crushing first increases and then decreases with the increase of initial particle size, but all are less than 40 mm; it increases approximately linearly with the increase of the discharge opening gap; and first increases and then decreases with the increase of rotational speed. The over-milled mass fraction shows a fluctuating upward trend with the increase of the initial particle size, a monotonically decreasing trend with the increase of the discharge opening gap, and a trend of first slightly decreasing and then slowly transitioning to a sharp increase with the increase of the rotational speed. These findings provide critical operational guidelines for deep-sea mining systems.