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Glass fiber reinforced plastics (GFRP) are composite materials with high strength and flame retardancy, and the disposal process is expensive to cause illegal dumping. Therefore, new recycling technology of waste GFRP are desired. In this study, recycling of waste GFRP using pyrolysis with sodium hydroxide (NaOH) under an inert atmosphere was attempted by gasification of resin and conversion of glass fiber into soluble sodium silicate. The pyrolysis behavior of GFRP, the characteristics of the obtained residue, the composition and the yield of generated gas, and the silica extraction into the solution were investigated. As a result, the gasification of the resin and the conversion of the glass fiber into soluble sodium silicate were promoted by pyrolysis with NaOH. It was confirmed that the gas yield, especially flammable gases (H2 and CH4), and the silica extraction increased and the residual ratio decreased as the increase of the heating temperature, NaOH addition and heating time.

Nitrate contamination of surface waters and groundwater is one of the main problems associated with agricultural activities worldwide, and there is an urgent need to develop effective materials and processes to remove efficiently excess nitrate from aquatic environments. Bittern is a seawater resource that contains large amounts of Mg2+ and Ca2+, and its utilization has received much recent attention. In this study, an Fe-type layered double hydroxide (Fe-LDH) product was prepared from bittern with the addition of an inexpensive agent (FeCl3) for nitrate removal. The greatest nitrate removal was obtained for synthesis conditions of pH 8.5–9.5 at 50°C for 0.5 h. The equilibrium adsorption capacity of the product for nitrate was measured and fitted with the Langmuir and Freundlich isotherm models. The experimental data better fit the Langmuir model than the Freundlich model. The calculated maximum adsorption capacity for nitrate was 0.40 mmol g–1, which was greater than those of other reported nitrate adsorbents. The product removed nitrate ions from a highly saline solution. The order of interference of anion species for nitrate removal was CO32– > SO42– > Br– > NO2– > Cl– > F–. The pH of the solution and removal of nitrate increased with increasing solution temperature because of ion exchange between the Cl– in Fe-LDH and the NO3– in the solution. Nitrate ions were repeatedly adsorbed and desorbed. The prepared Fe-LDH is expected to be a new inorganic anion exchanger for the removal and recovery of nitrate ions from aquatic environments.

Zeolites A and X, well-known as practical materials, were successfully synthesized with high cation exchange capacity (CEC) using two industrial wastes, waste crushed stone powder and aluminum dross, by alkali fusion treatment. Waste stone powder and aluminum dross are industrial wastes, and effective utilization of these wastes has been highly expected. Since the main components of the two wastes are Si, Al and O, those wastes can be used as starting materials for synthesis of zeolites. In this study, these industrial wastes were converted into crystalline zeolite-X and –A using alkali fusion. The stone powder, dross and the mixture of these wastes were transformed into a soluble phase via alkali fusion, and then agitated in distilled water at room temperature to give an intermediate gel-like solid, followed by synthesis at 80 °C to give the final product. The zeolites were successfully synthesized via the alkali fusion process, and selective synthesis of zeolites A and X was achieved by controlling the mixing ratio of aluminium dross to stone powder.

In this study, selective removal behavior of phosphorus from seawater using mechanochemical treated zircon sand was investigated. The product showed the same adsorption amount in seawater as that in the aqueous solution at pH 7, which means that phosphorus can be selectively adsorbed on the product in the solution with high salt concentration. The adsorption isotherm in seawater was found to applicable to Langmuir model rather than Freundlich model, and the calculated maximum adsorption amount was 0.01 mmol g-1. The adsorption kinetics of the phosphorus in seawater fit much better to pseudo-second-order model than to pseudo-first-order model. Phosphorus can be recovered from deep seawater using the column. Chloride and sulfate are not affected to phosphorus removal, while carbonate ion affects on phosphorus removal of mechanochemical treated zircon sand.

A novel carbonaceous immobilizing agent for heavy metal contaminated soil was prepared from rice straw using sulfur immersion and pyrolysis, and the lead immobilization in artificial contaminated soils using sulfur-impregnated carbonaceous material was estimated. The rice straws were cut to 1 cm pieces, and then immersed in 0.1 - 1 M K2S solution for 0 - 24 h to prepare sulfur-immersed materials. The immersed-materials were heated at 400 oC for 1 h in nitrogen gas to produce the sulfur-impregnated carbonaceous material by pyrolysis. The abilities of the product to immobilize lead from aqueous solution were examined to obtain the product with high lead immobilization ability. With increasing K2S concentration, the immobilization ability of the product for lead gradually increases and then above 0.5 M K2S those are almost constant, while 15 min is sufficient for the immersed time to obtain the product with high lead immobilization ability. The product prepared from material immersed in more than 0.5 M K2S solution for less than 15 min has a maximum immobilization ability for lead ion. The lead immobilization using the sulfur-impregnated product is sustainable due to the formation of leadhillite [Pb4SO4(CO3)2(OH)2] and anglesite [PbSO4]. The product can immobilize lead ion in various artificial lead contaminated soils. By mixing artificial lead contaminated soil with the sulfur-impregnated product, the eluted solution became neutral, and the eluted concentrations of lead ion dropped below the Japanese elution standard for soil.

The bamboo industry in Japan is declined, and disordered bamboo forests are increasing. Although maintenance of bamboo forest is needed, a large amount of bamboo wastes after logging is generated and left untreated. Therefore, new utilization of bamboo wastes after logging are desired. In this research, we aimed to develop a new recycling technology for bamboo using potassium hydroxide. By pyrolyzing bamboo using potassium hydroxide under an inert atmosphere, thermal decomposition of organic contents and alkali fusion of silica component inside the bamboo were carried out simultaneously to recover combustible gas, charcoal and silica component. The thermal decomposition behavior of bamboo, the properties of the obtained charcoal and extraction of silica in the presence of potassium hydroxide were investigated, and the optimum condition of bamboo recycling treatment was examined. As a result, it was found that when 1 g of bamboo was pyrolyzed at higher than 500 °C with 3 g of KOH, the almost silica was extracted, a large amount of fuel gas generated, and a carbonized material with specific surface area of about 1000 m2/g was obtained.

Removal of low-concentration fluoride in natural water is an important issue all over the world. Japan is a volcanic country with many hot springs, and the removal of low-concentration fluoride from hot spring drainage is desired. In this study, we attempted to prepare a novel adsorbent with high selective removal ability of fluoride from zircon sand using mechanochemical treatment, and applied it for removing fluoride from hot spring water. Mechanochemical treatment of zircon sand was carried out using a planetary ball mill, and fluoride removal of the product was examined using fluoride aqueous solution and hot spring water. The hot spring water is collected from one of the hot spring in Japan, and a typical sulfuric acid hot spring water pH 2 including high contents of SO42-(12000 mg L-1) and Cl- (5000 mg L-1) with 11 - 15 mg L-1 of fluoride ion. Regardless of ball sizes, with increasing the mechanochemical treatment time to 10 min, the removal ability of the product for fluoride increases, and then be almost constant. With decreasing pH of the solution to 2, the adsorption amount increases, and then be almost constant. With increasing the temperature of the solution, the adsorption amount decreases, while the rate of adsorption increases and the amount increases. The adsorption isotherm at pH 2 follows much better Langmuir model than Freundlich model, and the calculated maximum adsorption amount is 0.11 mmol g-1. Fluoride can be adsorbed selectively from hot spring water below Japanese effluent standard for fluoride (8.0 mg L-1).

In recent years, it has been considered to secure water and food using seawater desalination technology, and a new simple desalination material for reducing high concentration sodium chloride in seawater is required. In this study, desalting agents were prepared from natural zeolite with addition of calcined Ca-Fe type layered double hydroxide (LDH) to desalinate seawater for agricultural use. Mordenite type natural zeolite from Fukushima, Japan was used. The salinity and pH of seawater used in this study were 3.61% and 8.0, respectively. When more than 250 g/L of natural zeolite was added, the salinity decreased from about 3.56% to about 2.92% (reduction : about 18.0%) after stirring for 1 h. With higher dosage of calcined Ca-Fe LDH, the reduction time of salinity and the increase of pH became faster, while the reduction rate of salinity was almost same and pH value increased. When the mixture was used at the mixing ratio of natural zeolite and calcined Ca-Fe LDH was 5:4, the salinity decreased to 1.0% (reduction : about 70.0%) after stirring for 1 h, and the pH of the solution increased to 9.0 - 9.7. Radish sprouts could be harvested using seawater treated with a mixture of natural zeolite and calcined Ca-Fe LDH (5 : 4), while it was not possible to harvest using seawater and seawater treated with natural zeolite with lower addition of calcined Ca-Fe LDH.

In the crushed stone production process, waste stone-fine slurry is generated as wastewater, and are landfilled as dehydrated cake after some treatments. Recently, it is becoming difficult to secure landfill sites, and effective utilization of by-products, dehydrated cake, is desired. On the other hand, a large amount of coal fly ash was discharged from a coal-fired power plant, due to the operation suspension of nuclear power plants since the Fukushima nuclear accident occurs. In this study, we attempted to prepare geopolymer cement from waste stone-fine slurry with addition of coal fly ash. Waste stone-fine slurry used in this study was discharged from one of the quarries in Japan. NaOH solution was added into the slurry, and heated at 60 - 180 oC for 0 - 24 h to obtain the high Si solution for preparation of geopolymer cement. After heating, the slurry was cooled to room temperature by quenching with tap water, and various amounts of coal fly ash were added, mixed, and cured at 80 oC for 24 h. The strength and water purification ability of the product was examined. The solution with high Si content to prepare the geopolymer can be obtained at 120 oC for 9 h in 4 - 8 M NaOH solution, and the products obtained from 6 - 8 M NaOH slurry solution with addition of 0.55 - 0.70 weight ratio of coal fly ash have higher strength than other products and Portland cement. The product indicates NH4+ removal ability for wastewater treatment.

Steel converter slag, a by-product of iron- and steel-making plants, was converted into a product containing hydrocalumite-like compound using the alkali fusion method. Most of the crystalline phase in the converter slag was converted into a soluble phase by the fusion method, and could be transformed into a product which included hydrocalumite-type crystals. The ability of the product to remove BO3 −, F−, PO4 3−, AsO2 −, AsO4 3−, SeO3 2− and SeO4 2− from aqueous solution is higher than that of raw slag, especially for BO3 −, AsO2 −, AsO4 3− and SeO3 2−.

A novel carbonaceous immobilizing agent for heavy metal contaminated soil was prepared from bamboo using sulfur immersion and pyrolysis, and the lead immobilization in artificial contaminated soils using sulfur-impregnated carbonaceous material was estimated. The bamboo was powdered, dried, and then immersed in 0.1 - 1 M K2S solution for 0 - 24 h to prepare sulfur-immersed materials. The immersed-materials were heated at 400 oC for 1 h in nitrogen gas to produce the sulfur-impregnated carbonaceous material by pyrolysis. The abilities of the product to immobilize lead from aqueous solution were examined to obtain the products with high lead immobilization ability. With increasing K2S concentration, the immobilization ability of the product for lead gradually increases and then above 0.75 M K2S those are almost constant, while 15 min is sufficient for the immersed time to obtain the product with high lead immobilization ability. The product prepared from material immersed in more than 0.75 M K2S solution for more than 15 min has a maximum immobilization ability for lead ion of 2.78 mg/g. The lead immobilization using the sulfur-impregnated product is sustainable due to the formation of leadhillite [Pb4SO4(CO3)2(OH)2] and shannonite [PbCO3‧PbO]. The product can immobilize lead ion in various artificial lead-contaminated soils. By mixing artificial lead contaminated soil with the sulfur-impregnated product, the eluted solution became neutral, and the eluted concentrations of lead ion dropped below the Japanese elution standard for soil.

The desalination technology of seawater is considered to secure water and food in recent years, and a new simple desalting material to decrease the high concentration of sodium chloride in seawater is desired. In this study, preparation of the desalting agent from two Ca-type clay minerals, natural zeolite and Ca-Fe type layered double hydroxide (LDH), attempted to desalinate seawater for agricultural water[1][2][5]. Natural zeolites used in this study were mordenite-type zeolite from Fukushima prefecture, Japan and clinoptilolite-type zeolite from Kagoshima prefecture, Japan, and raw and Ca-substituted zeolites were used for seawater desalination[1][2][3][4][5]. Regardless of zeolite type, desalination behaviors of Ca-substituted zeolite were almost same as those of raw zeolite. The salinity and pH of seawater were 3.46% and 8.0, respectively, while clinoptilolite decreased the salinity to 3.20%, mordenite decreased to 2.09%, above 5.0 g/L zeolite addition. As increasing the Calcined Ca-Fe LDH addition to seawater, the salinity decreased to 3.3%, and pH of the solution increased to pH 11.5, and then became almost constant above 2.0 g/L addition of Calcined Ca-Fe LDH. As increasing the mixing ratio of Calcined Ca-Fe LDH to raw mordenite, the salinity decreased to 0.8% (79.2% reduction) while pH of the solution was neutral (about 7.6~8.0). Radish sprouts could be harvested using the seawater treated with a mixture of raw mordenite-type natural zeolite and Calcined Ca-Fe LDH, although those could not be harvested using seawater, the seawater treated with natural zeolite or Calcined Ca-Fe LDH.

In this study, it was tried to convert simulated lunar rock sand into geopolymer cement by alkali fusion with sodium hydroxide. Space development is currently being conducted in various countries. For construction on the moon, it is difficult to bring all the construction materials from the earth, and development of construction materials made from lunar resources is required. The authors have succeeded in making geopolymer cement from crushed stone dust using alkali fusion. Therefore, there is a possibility that geopolymer cement used for construction material can be made from lunar rock sand, abundantly present on the lunar surface, using the same method. In this experiment, simulated lunar rock sand was fused with NaOH by changing the mixing ratio of the sand and sodium hydroxide, heating temperature, heating time in vacuum or air atmosphere, and the reaction in vacuum and air was compared and examined. As a result, it was found that the elution contents of Si and Al in the fused sand into acid solution increased with increasing the temperature, NaOH addition and heating time of alkali fusion, and the fused reaction in vacuum atmosphere is different from that in air atmosphere.

Incinerated ash with a relatively high Ca content, paper sludge ash, was converted to zeolitic materials with high cation-exchange capacities (CECs) by aging at 80 &deg, C in NaOH solution via step-wise acid leaching with HCl to reduce the ash Ca content. The extraction of Ca, Mg, Si, and Al from the ash into the acid solutions during leaching and the products obtained from the leached ash by reaction with an alkali were examined. The contents of Ca and Mg in the ash were more easily extracted from the ash than those of Si and Al in the initial leaching. The leachant pH decreased with increasing numbers of leaching steps, and the amounts of Si, Al, and Ca extracted from the ash increased as a result of the dissolution of gehlenite (Ca2Al2SiO7), one of the main minerals in the ash. Zeolites A and P were synthesized from the leached ashes, and hydroxysodalite was synthesized from the raw ash. With increasing numbers of leaching steps of the ash, the obtained product contained lower released Ca, whereas the product contained higher released Na and has higher CEC, depending on the zeolite phases in the product. The product with the highest CEC was synthesized from third-leached ash, and its CEC was 1.5 mmol/g, which is about four times higher than that of the raw ash (0.4 mmol/g).

A circulating fluidized bed (CFB) reactor composed of a pyrolyzer and combustor was developed to observe tar emission during pyrolysis of low rank coal. Tar emission in the CFB pyrolyzer was examined under a wide range of operating conditions. Emissions of light tar substances (e.g., benzene, toluene, naphthalene, etc.) could be suppressed at 973 K by enhancement of contact between tar and resultant char in the pyrolyzer (i.e., enhancement of the volatile–char interaction (VCI)). It was also confirmed that about 50% of the heavy tar fraction emissions could be suppressed by the enhancement of VCI at 973 K. These trends were also observed at higher temperature (1173 K). A certain amount of heavy tar was emitted even after enhancement of VCI, so the mechanism of tar elimination was qualitatively determined using Spiral-type TOF-MS. The heavy tar was homogeneously deposited on the char and then was cracked to form lighter fractions by enhanced contact between tar and resultant char during pyrolysis.

A new carbonaceous adsorbent for heavy metals removal was prepared from paper sludge using sulfur impregnation. The sulfur-impregnated carbonaceous adsorbent with heavy metals removal ability can be obtained from sulfur-immersed sludge by pyrolysis. The product pyrolyzed at 400 °C has a maximum removal ability for nickel and lead ions, which has high specific surface area with sulfur-based functional to remove heavy metal ions. The product obtained at 400 °C indicates more effective removal for heavy metals ion than commercial charcoal, especially Ni2+ (66.7%) and Pb2+ (71.7%). With increasing pH of the solution, the adsorptions of Ni2+ and Pb2+ were increased and maximum removals of Ni2+ and Pb2+ were 99.6% above pH 7 and 100% above pH 6, respectively, The equilibrium data for nickel ion was found to fit the Langmuir isotherm better than Freundlich isotherm, with the calculated maximum adsorption capacity of 0.63 mmol/g, whereas the adsorption kinetics followed the pseudo-second-order kinetic model. The thermodynamic values, ΔG0, ΔH0 and ΔS0, indicated that adsorption was an endothermic and spontaneous process. The adsorbent can remove nickel ion from high saline water selectively. The desorption of nickel using H2SO4 solution is the most effective, but the cycle stability of the adsorbent is low.

Hydroxysodalite zeolite was synthesized at 90 oC from paper sludge ash, which is industrial wastes in paper manufacturing, using NaOH-LiOH mixed solution. Paper sludge ash was discharged from paper making plant as industrial wastes, and the amount is increasing annually. The new utilization of paper sludge ash is desired. Hydroxysodalite can be used to remove HCl gas at high temperature, and there are papers for hydroxysodalite synthesis from various ashes, for example, coal fly ash. In my previous study, hydroxysodalite can be synthesized from paper sludge ash. However, little information can be available on the synthesis of hydroxysodalite from paper sludge ash. Therefore, we attempted to examine the synthesis of hydroxysodalite from paper sludge ash using NaOH-LiOH mixtures. Hydroxysodalite [Na6Al6Si6O24‧8H2O] was obtained in the mixed solution with Li / (Li + Na) ratios smaller than 0.25, while katoite [Ca3Al2(SiO4)(OH)8] was formed in the mixed solutions with the other molar ratios, due to the dissolution of gehlenite [Ca2Al2SiO7]. The observed concentrations of Si and Al in the solution during the reaction explain the synthesis of reaction products, which depends on alkali species.

During quarrying, a large amount of waste stone dust is discharged as industrial wastes, and most parts of it dumps at landfill sites. The lack of landfill sites in Japan causes an increase of disposal cost, and new effective use is needed. In our previous studies, we attempted to synthesize zeolite from the dust using alkali fusion treatment to increase the solubility of silicon and aluminum in the dust, and we succeeded to synthesize faujasite zeolite from the dust. However, little information can be available on alkali fusion treatment of waste stone dust to synthesize zeolite. In this study, we attempted to treat continuously the dust by alkali fusion using a rotary kiln, and the effect of alkali fusion process on synthesis of faujasite from the fused material was examined. The mixture of the dust and NaOH powder with the weight ratios of 1:1.2, 1:1.4 and 1:1.6 was put into a rotary kiln, and heating at 400 -500 oC for 30 min, and the obtained fused material was converted into zeolite product by heating at 80 oC for 12 h followed by shaking 24h in distilled water at room temperature. It was confirmed that sodium silicate was formed using a rotary kiln, and the dissolution of Si and Al in the fused material increases with increasing NaOH addition. Faujasite can be synthesized on all fused conditions, and the cation exchange capacity of the product decreases with increasing NaOH addition. Regardless of fusion temperature, sodium silicate was formed using a rotary kiln, and the dissolution of Si and Al in the fused materials obtained on all condition are almost same. Faujasite can be synthesized on all fused conditions, and the cation exchange capacity of the product decreases with increasing temperature.