Many researches have been carried out on utilization of red mud wasted from bauxite processing, because it contains a lot of valuable components and environmental aspects. Researches are classified into several categories such as recovery of valuable components from thered mud, their utilization for building materials or for absorbents, and others. Although utilization of the red mud as building materials and as absorbents are attractive in a point that the red mud is used in bulk, they can not do anything without discarding valuable components such as titanium, zirconium and the main iron. Extraction techniques should therefore be developed for these elements in the red mud. Zeolite or hydrotalcite-synthesis connected with recycling of alkali-solution is a prospective way for effective use of the solution under the strong demand for the environmental protection in the world.

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It is considered that shape of a rock is one of the factors which dominate the falling behavior of the rock along a slope. Rocks were decided to be grouped into three shapes, namely massive, tabular and columnar. Shapes of 200 pieces of rocks were judged visually by 40 persons. A diagram for shape grouping was made by using the judged results of the shapes and the measured ratios of the lengths of minor and intermediate axes against major axis. Then an estimation method of a rock weight was examined considering rock shapes, from whichfollowing two points were clarified. 1) Coefficients of the equation for weight estimationare not infuluenced by the changes of the rock shapes. 2) Weight of a rock can be estimated reasonablly giving adequate value to α which is the correction coefficient for weight. Where, the value of upper limit of confidential interval should be used.

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This paper proposes a new method for optimization of ventilation network with a main fan in terms of minimization of the total cost which consists of the cost of power for ventilation and that of controlling resistances of airways. The elements to be considered in this method are the fan characteristics and resistances of the network. The proposed method yields the optimum fan operating point and resistances to be controlled. The following results are obtained through analyses of some examples by this method:
1. More energy saving control of ventilation network can be attained by the proposed method which considers fan characteristics than by others which do not.
2. Results computed by this method may notmake optimized values, when improper initial values of fan characteristics and resistancesare used. However, the optimum values will be gained by calculating again using the results of the previous calculation as the initial values for the subsequent trial.
3. Optimization is better when the required air quantities are constrained by lower and upper boundthan when given as fixed values.

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It is the purpose of the present paper to present a theoretical model of cutting slots with a steady highpressure water jet and a comparison with experiments. It order to predict the depth of the slot for both metal and rock, slot cutting has been described by one-dimensional excavation model. The progressive excavation of a rectangular element, illustrated in Fig. 6, has been analyzed, basing on the 6th power law on erosion which is experimentally formulated in the previous paper. In the present theoretical model, the depth of the slot is analytically solved by integrating the excavation speed of the rectangular element, defined by eq.(2), over the time of exposure, considering the effect of the pressure attenuation with the excavation.
The theory and experiments show that the depth of the slotis a function of the nozzle diameter, the driving pressure, the time of exposure, i. e. number of passes times the width of the rectangular element divided by the traversing velocity, the pressure attenuation constants and the standard erosion pressure that characterizes the objective materials. The main conclusion is that the standard erosion pressure of a rock is closely connected to its mechanical strength and nearly equal to the tensile strength of the rock. From that, it has been successfully verified, as shown in Fig. 12, that the theory agrees well with the single cutting experiments summarized in Table 1.

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The application of fuzzy logic to control concentrate grades in zinc cleaning column flotation was studied. Rules of thumb of the operation were obtained by interviewing operators.There are many variables to consider in the column flotation, but the initial strategy of the operators is to control the concentrate grade by adjusting the air flow rate. A fuzzy controller was developed based on this main rule of thumb and limiting rules for the tailings grade were added. A more stable and higher concentrate grade was obtained with the fuzzy controller. The total recovery was also satisfactory compared with manual operation. The fuzzy controller was further improved by the addition of rules of pulp level control.

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In removing the suspended fine particles from waste and muddy water, it is necessary to fasten their settling velocity by grouping particles as large flocs. Although nowadays organicflocculants have been used to flocculate suspended fine particles it is still hard to deal with the obtained sediment because of the moisture including in it. The use of non organic flocculant is unfortunately limited because of the tendency of flocculant ions to remain into the clarified water. So new flocculants should be developed to cope with these environmental problems.
In their previous studies on flocculation, dispersion phenomena and zeta-potential measurement of fine particles in aqueous suspension, authors had established that the zeta-potential of fine particles especially smaller than 6.54μm is one of the factors which rules the flocculation and dispersion phenomena since flocculation occurs between minerals with opposite sign of zeta-potential. Usually most of suspended particles in waste water have a negative value of zeta potential. So it is expected that the addition of minerals with a positive value of zeta potential such as fluorite will lead to thehetero-flocculation of particles and hence fasten the velocities of suspended particles.
In the present study, the effect of fluorite as flocculant has been investigated carrying out experiments on four types of fluorite sample (natural fluorite powder F93 and F92, artificial fluorite powder and suspension) and two types of waste water (fluorite flotationtailing from Kyoei Chemical Industry and bauxite residue from an alumina refining factory) It is noticed that fluorite suspensions have a better effect on flocculation of flotation tailing than fluorite powder. Besides artificial fluorite suspension even in small quantity is more effective than natural fluorite suspension. As for bauxite residue it is clarified by adding a large amount of artificial fluorite but the settling of flocs is very low (4mm/minute).

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Conventional turbidity method can not be used to estimate the cell growth of Thiobacillus ferrooxidans, because ferric precipitates (ferric hydroxide and jarosites) are formed in the medium due to bacterial oxidation of ferrous ions. In this paper, a modified turbidity method is proposed and demonstrated. The microorganisms were grown in 9K medium and the culture medium was sampled periodically. The sample medium was mixed with equal volumes of 6N HC1 to dissolve ferric precipitates. The precipitates dissolved completely after 30 minutes. The turbidity of the mixed solution was measured by nephelometer after the dissolution. During the culture, the turbidity increased exponentially, then reached a constant value, corresponding to exponential and stationary phases on the growth curve. The specific growth rate obtained from the turbidity curve agreed with the rate from the direct cell counting. The proposed method is more simple and rapid than the direct cell counting and protein assay that are usually used to estimate the cell growth of Thiobacillus ferrooxidans.
Using the modified turbidity method, the growth rates of Thiobacillus ferrooxidans in 9K medium containing 0 to 1, 000g/m³ of Tween 20, Brij 35, or polyethyleneglycol were investigated. With addition of 1, 000g/m³, all three polyoxyethylenes markedly suppressed the bacterial ferrous oxidation and cell growth.

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As part of studies on the development of separation process for efficiently separating waste plastics, the applicability of flotation method to the separation of inherently hydrophobic plastics has been investigated. For optimizing the flotation operation conditions, floatability measurements of plastics was carried out in solutions including wetting-agent, and flotation separation using two plastics mixture as well. Moreover, the dense media separation and flotation process, which has been proposed in this investigation, were examined in terms of the plastic grade and percent recovery. Polyvinyl chloride (PVC), polycarbonate (PC), polyacetal (POM) and polyphenylene ether (PPE) were used as test polymers, and tannic acid, sodium ligninesulfonate, polyoxyethylene lauryl ether, Aerosol OT and saponin as wetting-agents.
The floatability measurements showed that the increased concentration of wetting-agent brings about the decrease in percent floatability of each of polymers; this might be explained in line with adsorption behavior of surface-active species. Separation flotation using two plastics mixture indicated that one plastic is sufficiently separated from another in an optimum concentration of wetting-agent. Furthermore, the wetting-agent mixture was found to improve the efficiency of the separation flotation. Finally, according to the results obtained from the flotation tests, a dense media separation and flotation process was proposed and applied to the differential separation of the four plasticsmixture. It was found that the proposed process satisfactorily separated one plastic from others with high grade and recovery at each of the operations; the 100% PPE floats is obtained with 100% recovery in the dense media separation, the 95.7% PVC sinks with 90.7% PVC recovery in the first flotation, and the 87.6 % POM floats and the 90.3% PC sinks with 99.2% POM and 83.6% PC recoveries, respectively, in the second flotation. We suppose this separation process to be feasible for recycling waste plastics.

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Precipitation of cobalt carbonate from Co (NO₃) ₂-NaOH aqueous solution under high pressure carbonic acid (CO₂) gas was investigated experimentally using a glass autoclave. The results obtained in this experiment are as follows:
1) In Co (NO₃) ₂-NaOH aqueous solution under argon gas atmosphere, amount of precipitation increases while the pH of the solution remains nearly constant at 7.2-7.9 asNaOH concentration increases. However, the pH increases rapidly with NaOH concentration inthe region where the formation of precipitation ceases. 2) In Co (NO₃) ₂-NaOH-CO₂ aqueous solution, application of CO₂ gas makes precipitation absent in case of small precipitation amount and present in case of large precipitation amount in the initial Co (NO₃) ₂-NaOH aqueous solution. The pH ofthe solution is nearly constant at 6.0-6.5 in the region of higher NaOH concentration. 3) It was suggested that the precipitation formed in Co (NO₃) ₂-NaOH aqueous solution would be Cobalt Hydroxide, while the precipitation formed in Co (NO₃) 2-NaOH-CO₂ aqueous solution, would be Cobalt Carbonate or Basic Cobalt Carbonate.

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The precipitation of gelatinous aluminium hydroxide from aqueous solutions of aluminium chloride or nitrate by reaction with hexamine (hexamethylenetetramine) has been investigatedunder various conditions. The resulting precipitates have been examined by X-ray diffraction study, infrared spectrophotometry and thermal analysis (TG and DTA). As a result, it isfound that the composition of the precipitates depends on the experimental conditions, especially the pH value of aqueous solutions: amorphous aluminium hydroxide is precipitatedatpH 4 at 50 and 75°C, but not at 25°C; pseudoboehmite is accompanied by amorphous aluminium hydroxide at pH 5 regardless of temperature. In addition, when the precipitate isformed at lower temperature or from the aqueous solutions of aluminium salt at higher concentrations and/or on addition of hexamine rapidly, bayerite or hydrargillite is accompanied by amorphous aluminium hydroxide and pseudoboehmite. The composition of the precipitatesis little affected by the kind of aqueous aluminium salt solutions.

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