Katsunori Okaya

Grinding mechanism of centrifugal mills — a simulation study based on the discrete element method

Abstract This paper presents a model developed to simulate the family of ball mills, i.e. the tumbling mills, centrifugal mills, vibration mills and planetary mills, and its application especially to centrifugal mills in brief comparison with vibration mills. The model is based on the discrete element method (DEM) and is capable of describing the motion of balls and estimating the energy dissipation, classified by ball-to-ball impact (compression force), ball-to-ball friction (shear force), ball-to-wall impact and ball-to-wall friction. The model uses simple experimental data obtained by compression-crushing tests on particle beds and the restitution coefficient observed by ball-to-ball and/or ball-to-steel plate impact tests. The results obtained by the simulation indicate that the grinding action of centrifugal mills is largely dissimilar from that of vibration mills and that centrifugal mills provide a much higher energy dissipation rate per unit volume of the charge compared to vibration mills at an equal centrifugal coefficient. The results of the simulation imply optimum design and operating conditions of these mills.

Leaching of indium from obsolete liquid crystal displays: Comparing grinding with electrical disintegration in context of LCA

In order to develop an effective recycling system for obsolete Liquid Crystal Displays (LCDs), which would enable both the leaching of indium (In) and the recovery of a pure glass fraction for recycling, an effective liberation or size-reduction method would be an important pre-treatment step. Therefore, in this study, two different types of liberation methods: (1) conventional grinding, and (2) electrical disintegration have been tested and evaluated in the context of Life Cycle Assessment (LCA). In other words, the above-mentioned methods were compared in order to find out the one that ensures the highest leaching capacity for indium, as well as the lowest environmental burden. One of the main findings of this study was that the electrical disintegration was the most effective liberation method, since it fully liberated the indium containing-layer, ensuring a leaching capacity of 968.5mg-In/kg-LCD. In turn, the estimate for the environmental burden was approximately five times smaller when compared with the conventional grinding.

Development of a centrifugal mill - A chain of simulation, equipment design and model validation

Abstract A centrifugal mill was designed after a wide range of information obtained from the analysis on the mill model developed by the discrete element method. The simulation model is capable of predicting the ball motion, energy spectrum, map of energy dissipation in the mill body, etc., reconstructed from individual ball-to-ball and ball-to-wall interactions. Grinding tests conducted on the centrifugal mill developed were found to reproduce reasonably well the characteristics of the mill predicted by the simulation model. Since the simulation does not deal directly with the comminution performance itself, the major mission of the test work on the actual mill was to verify and to supplement the information acquired by simulation.

Concept of Seafloor Mineral Processing for Development of Seafloor Massive Sulfides

Seafloor Massive Sulfides (SMS), which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, is one of unconventional mineral resources beneath deep seafloors in the world. The authors have proposed the concept of seafloor mineral processing for development of SMS, where useful minerals included in SMS ores are separated on seafloor to be lifted while the remaining gangue is disposed on seafloor in appropriate ways. To apply column flotation, one of conventional methods in mineral processing, to seafloor mineral processing, the authors carried out simulating experiments of column flotation on deep seafloor using ores including copper, iron, lead and zinc as metallic elements. Prior to the experiments at high pressures, preparatory experiments at the atmospheric pressure were carried out to find out the optimum condition of the properties of pulp, a mixture of feed ore, water and chemical reagents. In flotation experiments at high pressures, formation and overflow of froth layer by bubbling were observed at 1MPa in both of pulps with pure water and artificial seawater. The analytical data showed that the concentration of metallic elements such as copper and zinc in the concentrates recovered from the experiments was higher than that in the feed ores while the concentration of silicon and calcium, which are assigned to gangue, in the concentrates was lower than that in the feed ores. These results suggest that column flotation can be applied to operation on seafloor.Copyright

Study on Grinding Technology for Seafloor Mineral Processing

Seafloor Massive Sulfides (SMSs), which are formed by precipitates from hydrothermal fluids vented from seafloor, have been expected as one of mineral resources to be developed. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor. To apply a ball mill to the grinding unit for seafloor mineral processing, grinding experiments were carried out using a small-scale ball mill applicable to high-pressure condition. In the experiments, wet grinding and water-filled grinding of size-classified silica sands were carried out at three rotation rates to compare the grinding performance in both cases. In both cases, the silica sands were finely ground. The measurement of particle size of samples from the experiments showed that water-filled grinding had comparable grinding performance to wet grinding while the suitable rotation rate for water-filled grinding shifted to higher than that for wet grinding. This result suggests the possibility of water-filled grinding for seafloor mineral processing. If water-filled grinding can be employed for the grinding unit, the structure of the grinding unit would be simplified in comparison with wet grinding that leads to the saving of grinding costs.Copyright

Boron Removal and Recovery by Adsorbing Effect of Boron on Thermally Treated Dolomite in the Water Containing Boron Ion

Dolomite is a double salt mineral, which consists of CaCO3 and MgCO3 that have different decarbonation temperatures. A particular modification is observed on the surface of mineral and the specific surface increased when dolomite was thermally treated at certain temperature. This investigation was carried out aiming at searching possibility of application of dolomite thermally treated at various temperatures for removing and recovering boron from aqueous solution. The confirmed best affinity adsorbent of boron is the heated dolomite at 750°C for 30 minutes. A series of experiments for adsorbing, and desorbing boron from a concentrated solution indicated the effectiveness of the thermally treated dolomite in terms of the adsorption capacity, which is similar or higher than the conventionally used adsorbents, such as activated carbon and fly ash. Thus, the results of this investigation suggested the adsorbent can effectively adsorb boron from drinking water or waste water, enabling the recovery of boron as new resource material.

Study on Seafloor Mineral Processing for Mining of Seafloor Massive Sulfides

Seafloor Massive Sulfides (SMSs), which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, has been expected as one of unconventional mineral resources on deep seafloors in the oceans. The authors have proposed the concept of seafloor mineral processing for SMS mining, where valuable minerals contained in SMS ores are separated on seafloor while gangue minerals are disposed on seafloor in appropriate ways. To confirm the applicability of column flotation, which is one of conventional mineral processing methods, to seafloor mineral processing, the authors carried out experiments simulating column flotation under the pressure conditions corresponding to the water depths down to 1000m in maximum using ore samples containing copper, iron, zinc and lead. In the experiments, formation of fine bubbles suitable to flotation and overflow of froth layer were observed at high pressures. The contents of copper and zinc in the concentrates recovered in the experiments at 1MPa were higher than those in the feed ores while the contents of silicon and calcium in the concentrates were lower than those in the feed ores. These results suggest that column flotation would be applicable to seafloor mineral processing.Copyright