Gravity separation is one of the ancient technologies for mineral processing and is still in widespread use. In recent years, many kinds of machinery for wet gravity separation have been developed and applied to process fine particles and solid waste.
The authors have reviewed newly developed machineries, in addition to the principle of wet gravity separation and conventional machineries. Most of them are conducted in gravitational fields or films of flowing water. The former harnesses the settling behavior of particles in water and the later the movement of particles in films of flowing water. The principles of these two methods and their state of application for commercial plants are detailed.
In gravitational field, Batac (TACUB) jig is a cost-efficient separator and provides better performance than Baum jig in coal preparation, where feed size is 0.5-200mm. Modified jigs are being developed to separate larger or smaller feed. The Wilfley table and Reichert cone are described as major machineries of film-flowing concentration.
Some centrifugal gravity concentrators have been developed because of the applicability of gravity separation to fine particles. A comparative review of typical centrifuge-type gravity concentrators is presented herein.
Two recycling plants using the TACUB jig are mentioned. One plant is processing waste concrete at 600,000 tons/year, and coarse aggregates are recovered and reused. The other plant was built to demonstrate that jig separator is efficient to separate and recover valuable plastics from scrapped office automation equipments.

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Currently more than 40 metals are systematically extracted and used in many different fields in civilized society. The quantities and qualities of the metals had been increasing after the Industrial Revolution. Especially, the pace continues to accelerate remarkably with advances in technology and globalization during the past several decades. The current frameworks of supply-demand for the metal commodities were assessed from the standpoint of the statistics, geology, and economics.
Wide ranging scope of quantity, market, price, and uneven distribution of geological factors are illustrated using a logarithmic scale. There is no general model or economic analysis applicable to all metal commodities.
Recycling and/or reuse have become very important because recycling contributes to supplying the material needs of society and protecting the environment. A number of factors that vary from metal to metal influence the recycling of old scrap. Values in old scrap recycling seem to be assessed based on various combination of four major factors, (a) primary production costs, (b) environmental benefits, (c) a fear of poisoning and (d) a fear of mineral depletion. As a result, it is not realistic that all waste materials are capable of being recycled, because recycling metals have fundamentally been competing with primary production.
Metal prices are determined by a number of factors, such as costs, technology, strikes, and policies that affect individually each metal price. It is observed that an immediate-run price rose often to few times that of long-run price due to extraordinary variables. For example, distinct properties of the six platinum group metals such as catalysts, stable electrical properties, resistance to chemical attack, and excellent high temperature characteristics have been exploited for industrial applications by advanced technologies during three decades. Since 1979, autocatalysts has emerged as the principal consumer of Pt-group metals. Platinum-palladium mix was used first to oxide the unburned hydrocarbons and carbon monoxide, and then it was replaced by a palladium-rhodium mix that oxide the unburned hydrocarbons and carbon monoxide and reduced nitrogen oxides according to the national legislation. Prices of Pt-group metals have alternatively risen and fallen, because they are determined in competitive markets based on balance of supply and demand. Fluctuations in Pt-group metals prices after 1970s mark a phenomenon not previously seen before using Pt-group metals in a number of their applications using advanced technologies

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A new type of confining vessel has been developed to undertake high-pressure, flow test experiments, at simulated lithospheric stress conditions. Confining pressure is generated by the uniaxial compression of a rubber medium, which leads to the term Rubber-Confining Pressure vessel ‰ (R-CPV) to describe this system. The pressure vessel is composed of an outside cylinder, an inside cylinder to hold the sample, rubber to generate the confining pressure and facilitate sample sealing, a hollow piston for rubber compression, and an outside piston for hollow piston compression and maintaining inner fluid pressure.
The fundamental principle of the R-CPV apparatus is the establishment of confining pressures which utilizes rubber elasticity to generate isotropic pressure. The rubber is bound to the sample and hollow piston only compresses the rubber. Pressure of compression is converted to confining pressure, which correspondingly affects the sample. The outside piston has holes for fluid inflow and outflow.
Testing of the R-CPV vessel, using butadiene rubber, has shown it can generate over 100 MPa maximum confining pressure, with 245kN pressing capacity, and facilitate permeability measurements under a range of high confining pressures. For example, preliminary results of flow test experiments for tension cracks in Inada granite, show hydraulic permeability rapidly decreases at <50 MPa confining pressure, whilst the apparent decrease in hydraulic permeability declines more gently at conditions of >50 MPa. Our experiments show that the new R-CPV apparatus has great potential for better understanding a wide range of geological issues, and likely industrial applications, as it can accommodate permeability-flow testing under a wide range of high confining pressure conditions.

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In recent years, long-term stability evaluation of rock structures has been becoming important increasingly. Especially, in the area of high level radioactive waste, it is necessary to evaluate the stability up to several 10,000 years. However, field measurement results and reliable information concerning the long-term behaviour of rock structures are very limited at present, and the prediction technique of the long-term behaviour has not been thoroughly established.
In this paper, first, the results of field measurement carried out for ten years in galleries at Tono Mine are described and discussed. The deformation was found to follow logarithmic law that is commonly observed in laboratory creep testing. FEM technique together with a constitutive equation of variable compliance type was used to simulate the deformation of galleries for ten years. The reasonable agreement between measured and calculated results was obtained indicating validity of the constitutive equation and the analysis technique.

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Constitutive relationships, which can relate stress state variables (net stress and suction) to strain state variables (void ratio and water content ratio) in swelling clay, are investigated in the present study. Additionally, the method to identify the nonlinear hydromechanical tangent moduli of swelling clay is given, in which transversely isotropic behavior of hydromechanical coupling is incorporated based on the experimental results obtained by the free swelling tests. The experimental results of the constant load swelling tests in uniaxial strain condition and free swelling tests are discussed. We find that swelling behaviors such as changes of void ratio, water content ratio, and saturation depend strongly on stress level and/or constrained conditions, and verify the predicted swelling behaviors in uniaxial stress and strain conditions by using finite element analysis.

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Loading rate dependency or time-dependent properties of the pullout resistance of fibers are indispensable to estimate the long-term stability of fiber reinforced concrete. In this study, the accurate and easy testing method recently proposed by the authors was applied to obtain the loading rate dependency of pullout resistance of fibers. The advantage of the method is that a few samples are enough for testing.
Pullout test was conducted pulling a single steel, PET or polypropylene (PP) fiber out of the mortar sample by a servo-controlled testing machine. In the test, displacement rate (pulling out speed of the fiber) was alternately changed between low and high values. Two pullout resistance-displacement curves corresponding to the low and the high rates were obtained. The difference of two curves indicates the degree of loading rate dependency of the fiber.
Experimental results indicate that steel fiber shows only very weak dependency suggesting that, in most cases, time-dependency is negligible small. Loading rate dependency of the peak pullout resistance for two plastic fibers was considerably stronger than that of steel fiber, though slightly weaker than that of mortar. After the peak value, loading rate dependency of PET fiber is becoming gradually weaker with increase of displacement. On the other hand, that of PP fiber is becoming stronger indicating more care should be paid for PP especially when PP reinforced concrete has been fissured or cracked.

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The green tuff from Hinai town, Akita is popular for architectural materials because of its beautiful pale green color and thermal and moisture retaining properties. When this stone is quarried and grinded for making products, approximately 60% of all quarried stone becomes the waste stone and it is required to be utilized effectively. Hinai-Green tuff is a porous media and it has abilities to neutralize acids and elute some minerals. These abilities may be effective for growth of microbes and our research group carries out the development of effective utilizations of Hinai-Green tuff as microbial activator. In this paper, the effects of Hinai-Green tuff on pH adjustment and microbial activities are described.
Hinai-Green tuff had an ability to neutralize both acid and alkaline water and especially neutralized acids effectivelly. For example, acid water of initial pH3 was neutralized to pH7 by adding 10(w/v)% Hinai-Green tuff into the acid water. Therefore, Hinai-Green tuff can neutralize acid soil and water and adjust acid environments to adaptable environments for microbes. Moreover, Hinai-Green tuff could buffer decrease in pH. The pH of water containing Hinai-Green tuff did not decrease rapidly with adding drops of 0.1M HCl, and especially the buffer action was strongly observed at pH 7 to 8. Hinai-Green tuff is very helpful to maintain pH appropriate for microbes for long time against decrease in pH caused by acid rain and/or acid metabolites of microbes. And pH adjustment effects of Hinai-Green tuff were caused by the ion exchange between Ca²⁺ leached from the stone and H⁺.
Consequently, microbes grew actively in a medium containing Hinai-Green tuff because of its pH adjustment effects. However, microbes did not grow in a medium containing natural zeolite from Futatsui town, Akita. The effects of Futatsui-Zeolite on pH adjustment for acid were low compared with Hinai-Green tuff.

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To reduce the volume of precipitates generated by the neutralization of acid mine drainage (AMD) containing high concentrations of Fe and As, the formation of ferrite using the precipitates was attempted by a two-step neutralization process in which calcium carbonate (CaCO₃) was used as the first neutralizer and sodium hydroxide (NaOH) as the second. Batch neutralization experiments with CaCO₃ and continuous flow experiments by the two-step neutralization were conducted in the laboratory and in an AMD treatment plant. The results showed that the precipitation of Fe, Al, Si, and As was primarily determined by pH and not by the kind of neutralizer. The precipitates in the ferrite sedimentation tank were magnetized in the continuous flow experiments, although the Al and Si prevented the generation of ferrite in the AMD and the precipitates contained calcite and gypsum as impurities. The molar ratio of As to Fe in the precipitates in the CaCO₃ sedimentation tank was estimated at approximately 0.01 at 2<pH<5. This suggests the coprecipitation of As and Fe. The mass balance calculation based on the results of the AMD treatment adopted here suggests that the amount of precipitates produced by ferrite formation is reduced by 15% for CaCO₃ and 67% for MgO compared with a conventional treatment.

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The diffuse layer model (DLM) of surface complexation modeling (SCM) was applied to discuss in the removal of dilute arsenic in wastewater. The equilibrium constants for complexation reactions of arsenic to ferric/aluminum hydroxide were based on several reference values and the total site capacity of ferric/aluminum hydroxide was determined by fitting to experimental results, since it is difficult to obtain surface area of amorphous hydroxide in wastewater system directly by experiment. The fitting results turns out that the total site capacity ratio becomes smaller as the concentration of ferric or aluminum hydroxide precipitates in wastewater increases. The experimental approximation formula between the total site capacity and the concentration of ferric or aluminum hydroxide precipitates was obtained. The model gave a quantitative correct description of experimental results for As(V) removal by ferric or aluminum hydroxide.
The above-mentioned examination was also applied to As(V) removal in waste water with SO₄. In Fe(III) salts, the total site capacities in wastewater with SO₄ became a little smaller than them in wastewater without SO₄, but in Al(III) salts, they are almost same value regardless of coexistence of SO₄. The removal of As(V) by ferric hydroxide at pH6 were predicted quantitatively by the model, also when SO₄ is contained.

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As a certain method for decomposing harmful asbestos, it is proposed to dissolve the asbestos in molten slag of the pyrometallurgical smelting furnaces. Several dissolution tests have been achieved so far, and it has been suggested that the crystalline structures of the asbestos were decomposed before dissolving into slag. In this study, asbestos samples composed of chrysotile or crocidolite were heated in temperature range 800-1000°C, and the times required to decompose the crystalline structures of the asbestos were examined using X-ray diffraction analysis. Temperature higher than 900°C was required to wipe off the peaks of crocidolite, though chrysotile could be decomposed at 700°C. For both samples containing chrysotile and crocidolite, the peaks of asbestos in the X-ray diffraction patterns disappeared almost within 90 seconds when heated at 1000°C. However, the needle shapes were still maintained in both samples when they were simply heated at 1000°C.

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