The discrete element method (DEM) coupled with fluid analysis was applied to describe the basic characteristics of media beads in a wet-type media agitation grinding mill, which is expected for ultrafine particles grinding or dispersion. Three types of agitator were compared by both of simulation and experimental investigation to know which one is suitable for ultrafine particles grinding and how the shape of agitator affects grinding performance. In the simulation, the collision energy and collision number between beads or bead and wall were calculated from kinetic energy at the instant of impact, separately in normal and tangential direction. On the other hand, the grinding rate and minimum ground size were obtained from experimental grinding results using calcium carbonate particles. The grinding rate had positive correlation to the average value of the collision energy between bead and wall, and the minimum ground size was correlated to the ratio of the collision energy in tangential direction to total collision energy between beads. This means that these two values obtained from DEM simulation are useful for a optimization design of a wet-type agitation mill. We also investigated the correlation between the collision energy for bead and wall calculated from DEM simulation results and the degree of abrasion in the wall observed in experimental grinding tests. At the part in which remarkable abrasion of wall was observed inside the mill, larger value of the collision energy between bead and wall was obtained from DEM simulation.
Horonobe Underground Research Center， located in northern Hokkaido， Japan， has been excavating shafts of underground research laboratory for R&D of radioactive waste disposal. In this site， the groundwater seepage from the shafts and leachate from the waste rock storage site contain high concentrations of total nitrogen. Ammoniumnitrogen， the major chemical species of nitrogen in the seepage and leachate， has been treated by the effluent treatment facility. However， the ammonium-nitrogen is transformed to nitrite- and nitrate-nitrogen (nitrification products) by nitrification. As a result， the concentrations of total nitrogen increase to the effluent guideline due to nitrification. Therefore， column experiments were carried out to understand the phenomena and the factors affecting the leaching behavior of nitrification products. The result showed that the nitrification was inhibited when the column layer was almost saturated， and that the nitrification occurred near the surface of waste rocks， in particular， at 25℃. These results indicate that nitrification can be mitigated by controlling the hydrological conditions in the waste rock storage site.
Electrolytic copper contains, on average, 10 ppm silver as impurity, which leads to a loss of silver as a cashcow product for copper smelters.Most of silver included in blister copper anodes passes into anode slime when electrolyzed, keeping the elemental state. However, once a part of elemental silver dissolves from the anode or from anode slime for some reason, then silver can co-deposit with electrolytic copper cathode, since silver is nobler than copper. In the present work, the dissolution behavior of silver from anode slime was examined by using granular silver as a model of the slime.We have shown that the silver dissolution is caused by dissolved oxygen in the electrolyte, and that thiourea and/or chloride ions as usual additives play a role to suppress the silver dissolution approximately to two thirds.Moreover, it was found that the dissolution of silver was suppressed to less than 1ppm by galvanic contacting of the granular silver with less noble metals (Pb or Cu) immersed in the same electrolyte. This indicates that the use of Pb or Cu lining at the bottom of electrolytic cells can suppress silver dissolution from the anode slime settled to the bottom, reducing the silver loss to electrolytic copper.
In the electrodeposition of aluminum (Al) from non-aqueous electrolytic baths, the contamination of the baths by water has been suspected to adversely influence the electrodeposition. In this study, we carried out the electrodeposition of Al from dimethylsulfone-AlCl3 baths containing various amounts of water to quantify the effect of water. Al deposits with uniform, smooth surfaces were obtained from the baths containing <180 ppm water, whereas deposits with dark, rough surfaces were electrodeposited from the baths containing >320 ppm water. A decrease in the current efficiency and an increase in the impurity content of the Al deposits were also observed with increasing water content of the baths. The measurement of the water content of the bath heated at 110 ℃ under an inert atmosphere revealed that the water content decreased with an increase in the duration of heating, indicating that the water could be eliminated through vaporization from the bath. The recovery of the current efficiency was confirmed by heating the bath for >24 h.