Rare-earths (RE) are indispensable materials for modern high-tech industries, and more than 90 percent of the demand of Japan depends on the export from China. However, a serious shortage and price soaring of RE have occurred since 2009 due to the export control of China. To secure a stable supply of RE, the government and private sectors of Japan have struggled to develop RE deposits other than China. In 2012, Mountain Pass (USA) and Mt. Weld (Australia) mines plan to begin the production of light RE, and their production will stabilize the supply and price of light RE. However, there are only some potential heavy RE mines other than China, and it would take at least two or three years for such heavy RE mines to begin their production.

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Ion-adsorption ores, which have been economically mined only in southern China, are weathered granites and are important supply sources for both LREE and HREE. As REE are electrostatically adsorbed onto weathering products (e.g., kaolinite) in the ores, they can be extracted by ion exchange using an electrolyte solution. Ion-adsorption type mineralization is constrained by the occurrences of REE-bearing minerals in parent granite and a change in pH of soil water, and is characterized by negative Ce anomaly. A series of studies on mineralogy, geochemistry, granite petrology and regional geology are acquired for understanding the genesis of ion-adsorption ores.

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Previously, it has been suggested that mercury from the submarine volcanic gas which had been ejected from the lowest points of the Wakamiko caldera in the northern part of Kagoshima bay, is the source of methyl-mercury contamination of the bay, where no chemical industries using mercury are located. However, it was reported in another study that 3.2 tons of mercury from mercury pesticides used from the latter half of the 1950s to the 1970s had flowed into the bay. Environmental research which relates to mercury in the bay, reported by the Environment Agency of Kagoshima Prefecture and other researchers from the 1970s till now, was epidemiologically re-examined for the purpose of checking whether the northern bay had been polluted in the 1970s by mercury from submarine volcanic gas or from mercury pesticides. The samples of seawater (n =234) from each layer in the bay were collected on May, July, October and January from 1974 to 1975. The samples of seawater from the surface layer containing mercury higher than 0.5 ppb were especially high during July (statistical probability p<0.001). Moreover, the total mercury concentration of seawater in the bay from 1975 to 1983 became lower year by year (p<0.001), and that for three years from 1975 was high in July and August (p<0.001). The high concentration of mercury detected in the seawater from the surface and upper layers of the bay in summer during the latter half of the 1970s could not be removed because of the formation of a deep thermal cline in the bay in summer. On the other hand, in 1994, when there were small-scale eruptions in the area, the total mercury concentrations of the surface seawater collected in April, June, July, September, November and December were the lowest in July (p<0.001), but the highest in December (p<0.001). The author, therefore, believes that the source of mercury which had polluted the environment of Kagoshima bay in the summers of the 1970s was mercury-pesticides used for rice blast fungus treatment which had been carried by river water, but not the submarine volcano gas ejected at the bottom areas of the caldera.

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Soil, mineral and clay become recognized as the source of pollution on groundwater and soil contamination at one time or another. Admittedly, groundwater contamination shall be deemed an event related closely to soil contamination, leaching hazardous substances to groundwater. And, the soil containing minerals with naturally-occurring heavy metals often contaminates soil and groundwater with artificial construction such as tunnel excavation. Sulfide minerals such as pyrite and arsenopyrite are thought to be the most likely causative substances of naturally-occurring soil contamination with heavy metals, occasionally leach heavy metals and make soil acidification after oxidizing by air and microbial activity. And then, contaminated soils with naturally-occurring heavy metals are identified into 3 classes and 2 leaching types with disposition about leaching of heavy metals and pH change. On the one hand minerals and soils are cause of contamination, but on the other hand minerals kindred class of clay are environmental-friendly materials to countermeasure of groundwater and soil contamination. There are mainly classed 8 types, clay minerals like smectite, allophane, zeolite, aluminum minerals, iron minerals, minerals containing calcium or magnesium, cement minerals and layered double hydroxide. The countermeasure technique such as immobilization and permeable adsorption layer using their minerals comes into wide use with acceptance. However, the countermeasure material was occasionally seen as ineffective against the contaminated substance from a lack of the comprehension about interaction mechanism between heavy metals and minerals, even if it is not used in effectual condition on the soil contamination site at that time. Therefore the activity for understanding to mineral interaction becomes recently promoted to get rid of such a blundering trouble.

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Zeolite A with Mg-Al layered double hydroxide (LDH) on its surface is prepared by a precipitation of LDH on zeolite A to be used for simultaneous removal of nutrients (ammonium ion and phosphate ion) from rivers and lakes. The zeolite A/LDH composite containing 35 wt% LDH showed ammonium adsorption up to 51 % in 5 mM ammonium chloride solution at pH 5.6 and phosphate adsorption up to 52 % in 0.5 mM sodium phosphate solutions at pH 7.0. Zeolite A covered with a hydroxyapatite on its surface is prepared simply by cation exchange of calcium loaded zeolite A with ammonium phosphate solution. This reaction forms a homogeneous layer on the zeolite A surface, and the resultant hydroxyapatite is a tightly bound to the zeolite A surface. This can be used for immobilization of radioactive strontium ion. The zeolite/hydroxyapatite composite showed high strontium adsorption ability. The maximum capacity was determined to be 0.40 mmol・g^<-1>, which was comparable to the value for zeolite A alone; this was because of the loose arrangement of hydroxyapatite nanocrystals on the surfaces. The composites obtained were then heated at 800℃ to 1,200℃ to improve the solution stability of adsorbed strontium ions. The elution of strontium ions in sintered composites was compared with those of sintered zeolite A in an alkaline solution (pH 10.2). Stability of strontium ions in sintered composites for solutions was improved with sintering temperatures over 950℃ as compared with those of sintered zeolite A because zeolite A, which forms feldspar phase after the sintering, is completely covered with hydroxyapatite crystals, which forms tricalcium phosphate after the sintering. Thus, we obtained a material which forms a barrier for elution and can be transformed into a stable material for storage of strontium. Zeolite composites with LDH and hydroxyapatite showed superior performance than zeolite alone in environmental purification applications.

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The viscosity of aqueous montmorillonite suspensions is affected by many factors, most notable among them include the soluble salt content and composition of exchangeable cations. However, difference in the viscosity of these suspensions remained even at almost identical soluble salt and exchangeable cation compositions. Because of these, the authors made this research based on the following hypothesis: the determining factor for the viscosity of aqueous montmorillonite suspensions is the aspect ratios of montmorillonite particles. Eight montmorillonite samples from Yamagata-Japan, Wyoming-USA and Gujart-India, having wide range of viscosity and aspect ratio, were used. In the experiments, the de-carbonated and Na-exchanged samples in addition to the untreated samples, both purified from bentonite suspension, were utilized. Surface area of basal planes and heights of 100 montmorillonite particles randomly-selected from the untreated samples were measured using AFM. The surface area of the basal planes was converted to the diameter of an equivalent circle. The aspect ratio was then calculated by dividing the diameter of the obtained equivalent circle with the height of the particle. The calculated values of the aspect ratio were at 260-380, 190-210 and 129 for the montmorillonites sampled from Yamagata, Wyoming and Gujarat, respectively. The aspect ratios of some Na-exchanged montmorillonite samples were also determined from the viscosity of diluted suspensions. The values of the aspect ratio obtained using this different method showed good agreement with the results by AFM measurement. This means that montmorillonite particles are suspended in water without folding or bending. For Na-exchanged samples, aspect ratio of montmorillonite particles and viscosity of aqueous suspensions showed good correlation (R^2=0.96). Using Simha's and Einstein's equations, the reason why the aspect ratio is the determining factor for the viscosity of aqueous montmorillonite suspensions could be explained as follows: in the aqueous suspensions, montmorillonie particles are rotating with Brownian movement of water molecules and occupying an apparent volume of sphere having diameter equivalent to the aspect ratio (nm). Apparent volume fraction of montmorillonite, which is calculated by multiplying the apparent volume of the montmorillonite particle and the number of particles in a 1ml suspension, is controlled by the aspect ratio. Because the aspect ratio affects numerically on the order of cube power to the apparent volume fraction of montmorillonite, while the number of particles in suspension affects only on the order of single power, in consideration of Einstein's equation. Montmorillonite that have large aspect ratios even with less number of particles will occupy a large apparent volume fraction in suspension and will have high viscosity. In contrast, montmorillonite with a smaller aspect ratio and large number of particles will occupy a smaller apparent volume fraction and the suspension will have low viscosity. Thus, the determining factor for the viscosity of aqueous montmorillonite suspensions is the aspect ratio of montmorillonite particles. Because this study was made using 8 montmorillonite samples having wide range of aspect ratio and viscosity, we believe that the conclusion obtained is universal.

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