As the earth has a finite amount of resources, resource-saving is important to maintain an affluent life. In Japan various types of Recycling Laws were implemented to promote a recycling-oriented society, and packaging materials, home appliance, automobile and personal computer are collected and treated for recycling. Waste plastics are utilized for substitute for blast furnace coke or fuel and also they are recycled as plastic materials. Developing advanced separation techniques which can treat the waste plastics at low cost and get high grade plastics are required to recycle the plastics with the same uses. This paper reviews recent developments in plastic-plastic separation techniques and describe future tasks. The number of cited references is 59. The mechanisms of each separation which contain gravity separation, electrostatic separation, flotation, and comminution are described and commercial scale and lab scale results are introduced. The characterizations of major plastic materials are also detailed.

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Since a fixed type of offshore structure such as deep-water platforms has lower natural frequency than approximately 5 Hz, this type of the structure can be easy of resonance to a seismic frequency. Hence, it is essential to avoid the state of resonance and/or so as not to maintain continuously its condition. This study has been done for the purpose of developing the vibration-suppression system applied mass-shift with discharging water, which is clean for the environment, and also economical. As the first step, a series of experiments were carried out by using the model-system, which can be discharged simultaneously water in a vessel from the cylindrical vessel on a upper deck, as soon as the structure initiated the lateral free vibration, corresponding to the above-mentioned resonance state.
As a result, it is shown that the vibration-suppression system proposed in this study can be realized on the model of experimental base.

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The removal of iron and various heavy-metal ions in waste water into stable ferrite-type precipitates at ambient temperature is a promising alternative to clean up large volumes of polluted effluents. In this study, quantitative evaluation of ferrite formation method from aqueous solutions containing iron and sulfate at ambient temperature was considered, toward future application of this method to the treatment of acid mine drainage containing iron. In order to evaluate suitable conditions of Fe₃O₄ formation quantitatively, these formation process was considered to be divided into two processes, i.e. oxidation process and aging process.
The reaction rate in the oxidation process was examined by aerial oxidation reaction test. The results showed that the oxidation rate of ferrous iron was determined by the mass transfer of oxygen from atmosphere to solution, so the yield of Fe₃O₄ in precipitation could be evaluated quantitatively by the total oxygen consumption which could be estimated from the oxygen transfer coefficient and the oxidation time.
The reaction rate in the aging process was also examined by solid-solid reaction test in which Fe(OH)₂ and FeOOH reacted directly in reduction atmosphere and at a fixed pH. At the initial stage of the reaction, the concentration change of FeOOH followed the first-order reaction concerning with FeOOH concentration. Surface complexation model which Fe(II) adsorbed to Fe(III) oxide could describe this phenomenon qualitatively.
Relation between quantitative indexes which investigated in this study and several reaction conditions such as pH, Fe concentration and stirring intensity agrees with the results of Fe₃O₄ forming reaction from aqueous solutions at 25 °c which have been investigated by us or other researchers. These quantitative indexes are useful to understand suitable conditions or mechanisms of ferrite formation.

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