Hajime Sugita

Leaching behavior of CRT funnel glass.

The leaching behavior of cathode ray tube (CRT) funnel glass containing 23 mass percent of Pb in 0.001 N HCl, distilled water, and 0.001 N NaOH at 90°C was investigated using a static method. The weight loss and leached amount of each component was measured and surface changes observed by SEM. The leaching mechanism is discussed. In acid solution, the leached amount of Pb showed t(1/2) dependence, that is, diffusion-controlled dependence, which is common in lead silicate glasses. In water and basic solutions, the leached amount showed saturation after higher initial dissolution than in acid and the deposition of many particles on the surface was observed. The amount leached was less for Pb than other components. The deposited particles formed a protective layer, which suppressed the dissolution of the glass. This dense layer must be formed as a result of a high initial dissolution rate.

Silica removal performance of seed from geothermal fluids

A seeding method, using colloidal amorphous silica seed made from geothermal fluid, has been tested as a silica scale prevention method. The effect on silica precipitation of the seed was examined experimentally. The results revealed correlations between the surface area and particle diameter of the seed and the mass of silica precipitated, and indicated that the seed exhibited highly reactive surface properties. The seed was confirmed to be of potential use as a silica removal reagent. Application of the seeding method to geothermal plants will guarantee the self-sufficiency of the latter as regards silica scale removal.

Scale Precipitation during Circulation of the Hijiori HDR Site, YAMAGATA, JAPAN

Several kinds of scale precipitated in the pipeline and production well during a two‐year circulation test in the Hijiori HDR system in Yamagata Prefecture, Japan. Amorphous silica and calcium carbonate scale tended to precipitate in the flow line, with the ratio of silica and calcium carbonate depending on fluid temperature and chemical composition. In the case of well HDR‐2, located closer to the injection well, the flowing wellhead temperature was about 120°C and the major scale was calcium carbonate, with a precipitation rate of 13mm/month. However, in the case of well HDR‐3, located further from the injection well, the wellhead temperature is about 160°C and there was a slight precipitation of amorphous silica scale. Anhydrite scale precipitated at the highest temperature zones in the deep part of the production wells because anhydrite has a reverse solubility curve and the fluid has a rich anhydrite composition dissolved from the rock of the deep reservoir.

Characteristics of arsenic in humic substances extracted from natural organic sediments

The stability and dispersion of naturally occurring As have been receiving increasing attention, because As is toxic and its contamination is a widespread problem in many countries. This study investigated As fractionation and speciation in organic sediments collected from different depositional settings to elucidate the existence of stable As in humic substances. Eleven organic sediment samples were collected from marine and terrestrial alluvial regions in Hokkaido prefecture, Japan, and the chemical fraction of As and species of humic substances were identified by sequential extraction. In addition, stable As bound in organic matter was evaluated by FT-IR spectroscopy. The As fraction mainly comprised inorganic substances, especially sulfur, iron, and manganese, and terrestrial sediments (lacustrine and inland deposits) were rich in sulfides and Fe and Al (hydr)oxides. When the residual fraction was excluded, the organic fraction of As was higher in seawater sediments than in terrestrial sediments. Among humic substances, cellulose, humic acid, and hydrophilic fulvic acid were clearly associated with As accumulation, and As speciation showed that the As was of organic origin. Cellulose, an organic compound of plant origin, was abundant in As=S and As (III)=O bonds, and As accumulation was higher in sulfur-rich peat sediments, corresponding with the physiological activities of As in plants. Hydrophilic fulvic acid and humic acid in these sediments, originating from small animals and microorganisms in addition to plants, denote higher As contents and abound in As (III, V)=C and C–H, CH3 bonds even in sulfur-rich sediments. The methylated As bonds reflect the ecological transition of organisms.