Based on an introduction of Japan's operation mechanism for exploiting deep-sea mineral resources, including Japan's marine policies, management and implementation agencies related to ocean mining, as well as Japan's coordination mechanisms for pushing progress in ocean technologies, Japan's cross-ministerial Strategic Innovation Promotion Program is outlined in terms of ocean mining, and the research achievements made by Japan in this field are also summarized. Such research on Japan's management system and program for exploitation of deep-sea mineral resources can be of reference for China in developing strategies, formulating investment mechanism and coordination mechanism for deep-sea mining.

With gold tailings as aggregate and ground gold mine tailings (referred to as gold mine tailings powder) as precursor materials, a kind of backfill material was prepared by alkali activation with sodium hydroxide together with sodium silicate as an activating agent. The effects of several factors, including particle size of gold mine tailings powder, modulus and addition of activating agent, on the mechanical properties of backfill mass were studied. The test results show that when gold mine tailings is ground for 60 min (size d₅₀ of 5.939 μm), modulus and addition of sodium silicate in activating agent are 1.2 and 60% respectively, the prepared backfill mass can have a 28 d compressive strength of 854.2 kPa, completely up to the requirement for backfill mass stipulated in the GB/T 39489—2020 "Technical Specification for Paste Filling with Total Tailings". Due to alkali activation, gold mine tailings powder is subjected to a hydration reaction, yielding a large amount of aluminosilicate gel, which forms a dense and stable structure, resulting in the backfill mass with good mechanical properties.

In order to define a mutual disturbance range between the upper and lower ore belts of a copper-gold mine during 8-year co-mining period, a deformation law of stratum by natural caving mining method is summarized based on the characteristics of stratum movement and deformation induced by mining. Combined with the actual mining technologies on site, a law of rock movement is explored for the lower ore belt by adopting engineering analogy method, theoretical calculation method and numerical simulation method, and the critical mining-induced disturbance range is defined to ensure safe mining of the upper ore belt, which provides a basis for the planning and layout for the mining of the lower ore belt. It is found that for safe mining of the upper ore belt, the lower ore belt should have security pillars of about 550 m along the strike, with the minimum angle of stratum movement within the range from 70° to 73.3°.

Based on the environmental characteristics of polymetallic nodules mining zone, different lifting modes for deep-sea polymetallic nodules, including continuous line bucket (CLB) system, autonomous submersible shuttle mining system and pipeline lifting system, were analyzed in terms of characteristics and applicability. With eight factors taken into consideration, including maneuverability, dry ore lifting capacity, launching and recovery efficiency, manufacturing and operation costs, suitability for water depth, adaptability to extreme sea condition and seabed disturbance, as well as environmental friendliness, a mathematical model covering multi-dimensional evaluation indices and an adaptability evaluation system were established. Analysis results show that CLB system and capsule pipeline lift system are not suitable for lifting polymetallic nodules, while autonomous submersible shuttle mining system, due to high cost in R & D, is not economically applicable. Due to the improvement in the reliability of underwater equipment and progress in the solution to sealing of heavy medium, pipeline lift system with heavy medium is expected to become a high-efficient lifting mode for deep-sea polymetallic nodules.

In order to accurately evaluate stability of surrounding rock of roadway with weak intercalation, an improved analytic hierarchy process and criteria importance through inter-criteria correlation (CRITIC) method, were adopted to determine comprehensive weight, and unascertained measure theory (UM) was used to determine unascertained measurement vector. Furthermore, the set pair analysis theory (SPA) was introduced to optimize confidence evaluation process, and then a UM-SPA coupling analysis model was established and used to evaluate the stability of surrounding rock of the roadway with weak intercalation in some gold mine. The results show that in-situ stress, tensile strength and thickness of weak intercalation are the main factors influencing the stability of such kind of roadway. The set pair potentials of sections D4, D5, D6, D7, and D9 belong to micro-reversal potential and tend to be unsafe. The stability of roadway at different levels is in the following descending order: 290^# level > 150^# level > 90^# level. The practical verification has proven that this model has an evaluation result consistent with the actual situation.

In order to improve the effect of deep-hole bench blasting in open-pit mines, a buffer blasting technique was proposed based on the on-site investigation of existing bench blasting parameters and rock fragmentation. In combination with simulation study by using LS-DYNA software and theoretical calculation, optimal borehole parameters and buffer thickness were finally determined, which were applied into the field blasting experiment. With buffer thickness of 5 m, borehole spacing of 5 m and burden of 4 m, the field blasting experiment brought an average fragmentation of less than 7%, showing a good blasting effect.

With support vector machine (SVM) optimized by whale optimization algorithm (WOA), a WOA-SVM hybrid model was established for predicting blasting vibration. Then, with root mean squared error and coefficient of determination as evaluation indices of the model, WOA-SVM model, SVM mode, Sadovsky's model and USBM model were compared based on the data of blasting vibration in Sijiaying Iron Mine. A comprehensive evaluation shows that the WOA-SVM model is superior to other models in terms of prediction accuracy.

The adsorption mechanism of La³⁺ and NH₄⁺ ions on (001) and (00-1) planes of kaolinite has been studied based on the first-principle calculation of plane-wave pseudopotentials of density functional theory. The results show that La³⁺ ions are mainly adsorbed on kaolinite surface through electrostatic interaction, while NH₄⁺ ions are adsorbed thereon through both electrostatic interaction and hydrogen bonding, with more electrons transferred onto kaolinite surface than La³⁺. The absolute values of adsorption energy for ions on (001) plane of kaolinite are in the following descending order: La³⁺ > NH₄⁺ > H₂O, while on (00-1) plane in the following descending order: NH₄⁺ > La³⁺ > H₂O. It is found that La³⁺ ions are prone to be adsorbed on (001) plane, while NH₄⁺ ions are prone to be adsorbed on (00-1) plane. When ammonium sulfate is used as a leaching agent, rare earth ions like La³⁺ adsorbed on the (001) plane can only be effectively displaced with the leaching agent at a certain concentration.

A commercially applied large ball mill with an effective internal diameter of 4.6 m is taken for study, and the discrete element method (DEM) was introduced to simulate and investigate the influence of filling rate of grinding media (steel balls) on the collision of particles inside the mill and energy consumption. It is found that when the filling rate of grinding media is 30% - 35%, the frequency of ball-ore collision increases gradually. However, the ratio of ore-ore collision frequency to the total collision frequency increases first and then decreases, and the energy loss for ball-ball and ball-liner collisions increases. It can be seen that increasing filling rate of grinding media may not only reduce grinding efficiency and increase energy loss, but also increase liner wear by steel ball, which is not conducive to sustainable usage of mill liner.

In order to explore the influence of ultrafine grinding using high-pressure grinding roller (HPGR) on the separation performance of copper-bearing iron ore, mineral separation tests were carried out for HPGR milled ore. The results show that HPGR products are usually smaller and more uniform in size compared to jaw crushing products. Furthermore, obvious grain boundary cracks in HPGR products can be observed. Based on the comparison with jaw crushed ore, a test on magnetic separation of HPGR milled ore for tailings discarding led to the obtained product with iron grade up by 0.4 percentage points and iron recovery down by 0.8 percentage points, while both copper grade and recovery up by 0.01 and 2.11 percentage points respectively. A flotation test resulted in the roughing concentrate with copper grade and recovery up by 0.21 percentage points and 1.84 percentage points, respectively. The following magnetic separation test of the obtained roughing tailings led to the final iron concentrate with grade and recovery up by 1.11 and 2.45 percentage points, respectively. It is concluded that compared with jaw crushing, HPGR grinding is more conducive to improving copper grade and recovery of iron concentrate.