The objective of this study is to evaluate the effect of acids on light rare earth elements dissolution from weathered residual rare earth ore after mechanochemical reaction by grinding. In the case of sulfuric acid leaching, the maximum of light rare earth elements dissolution was obtained when the initial sulfuric acid concentration was 5.0 mol/dm³ and leaching time was 24 hours. Thus, we performed sulfuric, hydrochloric and nitric acid leaching experiments at the same condition. The obtained results highlighted that the best light rare earth elements dissolution among these acids achieved by hydrochloric acid leaching. On the other hand, equivalent light rare earth elements dissolution except cerium was achieved by nitric acid leaching. From x-ray absorption fine structure analysis, it was revealed that cerium oxide(IV) (CeO₂) was produced after nitric acid leaching because of redox reaction between cerium and nitrate ion.

Zeolitic imidazolate frameworks (ZIFs) are a novel class of porous materials composed of metal ions and imidazole linkers. Here we focus on core-shell particles, where ZIF-67 core particles are covered with ZIF-8 shells (ZIF-67@ZIF-8). However, the synthesis of ZIF-67@ZIF-8 is generally difficult because the nucleation rate of ZIF-8 is so high that self-nucleation is unavoidable. In this study, we propose the following two approaches to overcome this challenge: (1) decreasing the nucleation rate by changing the water to methanol ratio used as solvents; and (2) intensifying the mixing during the synthesis by using a microreactor. Our experiments demonstrated that an increase in the water ratio suppresses the self-nucleation of the ZIF-8 particles, whereas surfaces of the resultant ZIF-67@ZIF-8 particles become irregular. The ZIF-67@ZIF-8 particles with uneven surfaces experienced an approximately 14% decrease in the adsorption amount as compared with that of the ZIF-67 particles. In contrast, the microreactor successfully produced ZIF-67@ZIF-8 particles with a smooth surface and high surface area. Our study revealed that intensive mixing is key to obtain uniform core-shell particles.

Liesegang phenomenon has been extensively studied experimentally and theoretically in the field of nonlinear science. However, there are few studies for its applications due to the high nonlinearity. The particles produced with the Liesegang phenomenon have been limited to microparticles of sparingly soluble salt for many years. In this study, in anticipation of more engineering application of this phenomenon, gold nanoparticles are synthesized by diffusing gold ions into a gel containing a reductant. At that time, we investigate the influence of diffusion conditions on particle formation. As a result, we found that the size of resultant particles depends on the gel position. Furthermore, we construct mathematical model expressing ion diffusion and particle growth based on Ostwald ripening to discuss the particle formation mechanism.

Empirical forms for the strengths characterizing stability of a horizontal tunnel in wet granular matter are experimentally derived. The motivation of this study comes from the observation of crab burrows on sandy beach. To understand the mechanical constraints for constructing the stable burrow structures, we perform a set of simple experiments with a horizontal tunnel structure made in a wet granular layer. Then, the tunnel is compressed from the top of the layer using a universal testing machine. During the compression, the shrinking tunnel shape is captured by a camera. Using the measured compression force, stroke, and shrinking tunnel images, we define and measure the mechanical strengths of wet granular matter with a horizontal tunnel. By systematically varying the experimental conditions, we obtained the empirical forms for estimating strength values. Using the measured results, we briefly discuss the mechanical conditions of sandy crab burrows.

It is important to reveal fault structures and stress states in accretionary prisms for understanding the building and releasing of seismic energy as they control the generation of great earthquakes and tsunami. Here we show the evolution process of three-dimensional fault structures on sandbox simulations using a discrete element method (DEM). To realize the real-scale sandbox simulation, we developed state-of-the-art techniques in high performance parallel computing methods for the DEM, and then performed the largest DEM simulation in the world using up to 1.9 billion particles with similar grain size of real sand for identifying the three-dimensional fault structure. The DEM simulations reproduced the undulation of fault structures similar to those found commonly in nature. In addition, the characteristic grain motion was found near the frontal fault before beginning the uplift event of sand bed, which could be a precursor of tectonic events behind accretionary prism formation.

The interaction between dry granular materials and a plate is numerically studied using a large-scale discrete element method (DEM) simulation. In the simulation, a vertical flat plate is dragged horizontally through closely packed materials. To examine the effects of particle size on the drag force acting on the plate, five cases with different mean particle diameter D_p50 = 4.0, 2.0, 1.6, 1.2 and 0.8 mm are compared. The results show that for larger particles, the force randomly fluctuates as the plate advances while for smaller particles, the force oscillates with a larger amplitude. The analysis of angular velocity of the particles shows that the force oscillation is attributed to the evolution of shear bands formed only in the bed of the smaller particles.

A new method to determine both the coefficients of particle and rolling friction in distinct element method (DEM) was proposed. The coefficients are two of the most important parameters which have great effect on particle behavior in DEM. However, it is difficult to determine the values of the coefficients, which is applicable to multiple behaviors, from an experiment. We proposed the method to determine the two coefficients uniquely so that two indicators correspond to experimental results. As the indicators of static and dynamic behaviors, the angle of repose and the discharge flow rate were adopted, respectively. The values of the coefficients which can represent both static and dynamic behaviors of particles were determined by means of the method. The particle behavior in a rotating drum at three different rotational speed was simulated by using the determined coefficients in order to verify the applicability of them to dynamic behavior of particles under various conditions. The simulated behaviors for spherical particles corresponded to the experimental ones. The determined coefficients by means of the proposed method could be applied to the behavior of spherical particles at all of the rotational speeds. On the other hand, the simulated behaviors for irregularly shaped particles did not correspond to the experimental ones, in particular at higher rotational speed. It would be because the rolling friction of irregularly shaped particles depends on the particle velocity in a rotating drum.