Jig separation is an ancient technology in mineral processing and it is still in widespread use. In recent years many kinds of varieties on jig separation have been developed and applied to process fine particles and solid waste. The authors reviewed the technological development in jig separation and discussed how innovations occurred, relating to hand jigs used from the 16^th century, and jig separators developed in the 20^th century, moving screen, fixed screen, and rotating screen types. Recently developed jig separators for processing fine particles, larger particles and plastics are reviewed including the Rom jig, centrifugal jigs by Altair and Kelsey, and the packed column jig. Newly developed jig separators by the authors, RETAC, Hybrid and Reverse jigs, are introduced discussing the principles and applications behind the developments.

View full abstract

To estimate long-term deformation and stability of underground structures, it is indispensable to understand time-dependency of rock sample and rock mass. Previous experimental and theoretical studies showed that rock strength was proportional to the 1/(n+1)-th power of loading-rate and creep lifetime was inversely proportional to the n-th power of creep stress, where n was a constant depending on rock type and testing environment. The smaller value of n, the larger time-dependency of rock, which suggests that n can be a useful index of time-dependency. This paper introduced three loading and a creep testing methods to obtain the value of n, and showed their results in uniaxial compression, uniaxial tension and Brazilian tension tests for 38 rocks in the country and overseas. Many rocks showed smaller values of n under water-saturated than air-dried condition. The value of n was proportional to strength under water-saturated condition or low confining pressure, but not under high confining pressure under which failure was more ductile. Rock mass classification systems considering time-dependency of rock were examined as an application of testing data on design or construction of underground structures. An index n was implemented in four classifications, RMR, Q, GSI and RMi, and their proposed equations indicated that rating decreased with an increase in duration of use of structures or in degree of time-dependency of rock mass.

View full abstract

Chain Conveyor Cutter (CCC) is a chain saw type machine developed for deep mixing ground improvement. Unlike ordinary chain conveyors, CCC is installed on a pile driving rig and is penetrated down to and lifted up from the ground excavating and vertically mixing the cut soil with cement slurry. CCC consists of a drive unit, a return unit, a conveyor trough of the middle post and chain units. Chain units consist of twin strand link chains, scraper bars and conical bits mounted on bit plates installed on the scraper bars. While being sunk into the ground, running bits cut soils around the return unit at the bottom of the machine injecting cement slurry and haul up and down the cut soils and slurry making use of its conveyor function. The cutting ability of CCC is based on the 180kW water cooled electric motor and the weight of the machine. The maximum cutting force reaches around 600kN and the weight is more than 20t, which enables CCC to deal with versatile types of soils as hard as soft rocks. The mixing ability of CCC is based on the vertical conveyor effect of the chain unit. Twin strand outboard chains, a scraper bar and a bit plate on the scraper bar form a structure like a bucket. The buckets vertically run on the troughs presented by middle posts and haul up and down the slurry and soils from the bottom of the machine. The cyclic movement of the slurry and the soil contribute to establish uniform soil cement bodies. In the actual operations, CCC encountered hard materials like gravels, conglomerates and artificial debris, which caused damages to the chain units of CCC. Those damages made it so clear the necessity of sophisticated chain speed control system that inverter control system was developed and introduced. CCC constructed approximately 2,000m cut-off walls surrounding settling ponds for receiving dredged materials in the port of Miike restoring works.

View full abstract

Only the very limited knowledge has been known concerning the mechanical properties of coal under uniaxial tensile stress which are very important factors in coalmines. In this study we carried out uniaxial tension tests on coal, with particular attention to find the most appropriate constitutive equation for the sample coal. Three constitutive equations were chosen and tested, among which two had been proposed by the authors and one was newly proposed in this study. Coal showed high sample-to-sample scatter in strength and Young's modulus, however, relatively small scatter in the normalized stress-strain curves in the pre-failure region. All three constitutive equations were found to represent the complete stress-strain curves in reasonable accuracy. This result presents a successful application of the authors' constitutive equations to the coal behavior under uniaxial tensile stress. Once these equations are determined, they can be incorporated into FEM software to investigate various time-dependent behaviors of coal and aid in the efficient design of coalmines and the prevention of coalmine disasters.

View full abstract

DCDA is a new method for evaluating the in-situ stress of rocks based on the elliptical deformation of boring cores with stress relief. When a rock core sample is carved out by drilling, it becomes free from in-situ stress, and the expansion should occur elastically. If the condition of in-situ stress is anisotropic, the core must deform in an asymmetric manner. With the precise measurement of core diameters in each directions, the deviatoric stress S_Hmax －S_hmin and azimuths of S_Hmax and S_hmin could be determined from the circumferential variation of the measured diameter. In order to confirm the reliability of DCDA, laboratory verifications were conducted. The estimated stresses by DCDA agreed well with the applied stresses, and the directions of d_max coincide to the directions of the applied stresses. From these results, the effectiveness of DCDA was confirmed.

View full abstract

Reverse osmosis/nanofiltration (RO/NF) membranes are attractive water purification technologies because of the capability to provide an effective barrier for a wide range of contaminants in a single treatment step. However, solute permeation mechanisms by RO/NF membranes remain to be fully elucidated. The objective of this study was to perform permeation experiments using two commercial polyamide RO membranes under various pH and hydraulic pressure conditions, and to analyze the permeation data with a transport model with the goal of evaluating the importance of advective solute permeation. The experimental data and subsequent data analysis revealed that the main permeation mechanism for As(III) and NO₃^- through RO/NF membranes was partition-diffusion mechanism and advective transport is not a dominant permeation mechanism. On the other hand, adevective permeation played a more important role for Cl^- and accounted for more than 50% of total Cl^- permeation depending on treatment conditions. These results indicate that the rejection of Cl^- could be significantly improved by forming polyamide active layers with the absence of nano-scale pinholes. However, the RO membrane having higher advective water permeability was found to have a thicker and smoother polyamide active layer, meaning these physical properties were not correlated with the occurrence of nano-scale pinhole formation in polyamide active layers.

View full abstract

Glass samples of Na₂O–P₂O₅–SiO₂ containing Nd₂O₃ with ～0.3 mol% were prepared by melting on a hotfilament and quenching. Absorption spectra of 4f-4f forced-electric dipole transitions of Nd³⁺ were evaluated with a commercial spectrophotometer. Local structures around Nd³⁺ ions were estimated by the shape, peak wavelengths, and absorbance of ⁴I_9/2→⁴G_5/2, ²G_7/2 and ⁴I_9/2→⁴F_5/2, ²H_9/2 transitions with the interpretation of previous results concerning EXAFS analysis. Absorption spectra indicate that the composition at which Nd³⁺ ions are selectively coordinated by PO₄ tetrahedra is [Na₂O]/[P₂O₅] 2 in a molar ratio for Na₂O–P₂O₅ glasses and [Na₂O]/[P₂O₅] 1 for Na₂O–P₂O₅–SiO₂ glasses. IR spectroscopy results the glasses mainly consist of PO₄ Q² units and P–O–P bonding. Elution tests reveal that Nd constituents, coordinated with PO₄ tetrahedra, with a large fraction of ～0.9 were dissolved into ultra-pure water at 30ºC for the phosphosilicate glasses with [Na₂O]/[P₂O₅] 1.

View full abstract