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We have attempted to synthesize layered double hydroxides (LDHs) adsorbents that can selectively remove harmful substances such as boron (B) and mercury (Hg) contained in wastewater. The calcined CaAl-LDH demonstrated high B removal performance of 96% in the B solution coexisting with sulfate ions. The calcined CaAl-LDH forms ettringite and incorporates B into the crystals, achieving a level of purification below the effluent standards. Furthermore, [S_3]^2- intercalated MgAl-LDH can selectively remove Hg from Hg-contaminated water containing Mn and Fe ions.

In order to purify waste water containing fluoride, the calcium additive method has usually been used to recover fluoride ions in the form of refractory calcium fluoride. In this case, the removable fluoride concentration is limited to be 10-15 mg/l due to the solubility of calcium fluoride. In this study, we report 3CaO・Al_2O_3・3CaSO_4・32H_2O (ettringite) as a highly absorbent substance for the fluoride. The fluoride concentration of the water treated with the ettringite was achieved to be less than 8 mg/l without sludge.

In order to purify waste water containing fluoride, the calcium additive method has usually been used to recover fluoride ions in the form of refractory calcium fluoride. In this case, the removable fluoride concentration is limited to be 10-15 mg/l due to the solubility of calcium fluoride. In this study, we report 3CaO・Al_2O_3・3CaSO_4-32H_2O (ettringite) as a highly absorbent substance for the fluoride. The fluoride concentration of the water treated with the ettringite was achieved to be less than 8 mg/l without sludge.

Heavy metals in sediments after treatment of mine wastewater from Ogoya Mine, Ishikawa Prefecture, Japan, was mineralogically investigated. Acidic wastewater (pH 3.5) which flows out from pithead, contains high concentration of heavy metals. In this mine, neutralizing coagulation treatment is going on using slaked lime (calcium hydroxides: Ca (OH) 2). Core samples were collected at disposal pond to which treated wastewater flows. Mineral assemblages and chemical compositions of core samples were analyzed. X-ray powder diffraction (XRD) analyses indicate that upper parts of cores are rich in calcite, whereas deeper parts of cores are rich in gypsum and ettringite. Smectite with heavy metals are found in 87-90cm of core samples. Scanning Electron Microscopy (SEM)-Energy Dispersive X-ray analyses (EDX) and Electron Probe Micro Analyzer (EPMA) show that heavy metals, such as, Fe, Mn, Cu and Zn are concentrated in calcite, gypsum, ettringite, and clay minerals. The results indicate that heavy metals in wastewater are mineralogically fixed in solid phases of calcite, gypsum, ettringite and smectite.

金沢大学理工研究域地球社会基盤学系, 尾小屋鉱山の坑口(第六立坑)からは,現在も高濃度の重金属を含む酸性の廃水(pH3.5)が流出し続けており,消石灰の投入による中和凝集沈殿処理が行われている.処理後の廃水が流入する沈殿池から採取したコアサンプル(44層)の鉱物組成をX線粉末回折(XRD)によって,また含有元素の割合をエネルギー分散型蛍光X線分析(ED-XRF),NCSコーダーによって分析した.コアサンプルの上部には茶褐色の層が多く,下層になるにつれて色は薄れていく.茶褐色は含有するFeの量により,それらは低結晶性の水酸化鉄鉱物の存在を示唆し,Cu,ZnおよびPbが吸着していると考えられる.また,Sの含有量は深層になるに従って多くなる.カルサイトはコアの上層部に多く,下層部にはエトリンガイトが形成されているが,Cdの含有量はカルサイトやエトリンガイトと同じようなプロファイルを示す.その他,堆積物中には,ジプサム,石英,ブルーサイトが認められた.Caは上層部ではカルサイトとして,また,下層部ではエトリンガイトとして堆積している.本研究により,消石灰の投入によって中和処理された鉱山廃水中の重金属イオンは,水酸化鉄,カルサイト,エトリンガイトに伴って堆積,蓄積されていることが明らかになった., Depositional formula of heavy metals after disposal of the mine drainage from the Ogoya Mine in Ishikawa Prefecture, Japan, was mineralogically investigated. Strong acidic wastewater (pH3.5) from pithead of the mine contains high concentration of heavy metals. In this mine, neutralizing coagulation treatment is going on by slaked lime (calcium hydroxides: Ca (OH)_2). Core samples were collected at disposal pond to which the treated wastewater flows. The core samples were divided into 44 layers based on the color variation. The mineralogical and chemical compositions of each layer were analyzed by an X-ray powder diffractometer (XRD), an energy dispersive X-ray fluorescence analyzer (ED-XRF) and a NCS elemental analyzer. The upper parts are rich in brown colored layers, whereas discolored are the deeper parts. The color variation is relevant to Fe concentration. Brown colored core sections are composed of abundant hydrous ferric oxides with heavy metals, such as Cu, Zn, and Cd. On the other hand, S concentration gradually increases with depth. XRD data indicated that calcite decreases with increasing depth, and ettringite is produced at the deeper parts. Cd concentration shows similar vertical profile to those of calcite and ettringite. The results revealed that hydrous ferric oxides, calcite and ettringite are formed on deposition, whereby incorporating the heavy metals.

金沢大学理工研究域環境デザイン学系, Kawamura, Mitsunori | 20019730

金沢大学理工研究域地球社会基盤学系, Mortar bars are exposed to H2S gas (25-300ppm) for 10 months at 12-30C°. Sulfate-generated deteriorations in the mortar bars include expansion, cracking and disintegration. The heavily corroded mortar bar produced gypsum, calcite and secondary ettringite with a trace amount of barite. The secondary ettringite shows the same chemistry as the primary ettringite, but the morphology is quite different from the primary one. Ettringite crystals with sharp point, 10-20μm long, are primary formed during the hydration of mortar bar, whereas small lath-shaped crystals, about 3μm long as observed by SEM are high concentration of hydroxyl ions. Gypsum, calcite and the secondary ettringite are formed step by step under acidic condition. The iron oxides layer is presented significantly between corroded and un-corroded zones which is the same process of deterioration on portland cement concrete.

Recently, chemical soil stabilizations are actively adopted for the improvement of the soft ground on which the road and the foundation for offshore structures will be constructed. The industrial by-products such as gypsum, coal ashes, blastfurnace slag and basic oxygen furnace slag can be used effectively for the soil stabilization. In this paper, the characteristics of soil stabilizations with various industrial by-products are discussed from the viewpoints of the types of reaction products which are responsible for the development of strength in the stabilized soils.