Gyrolite (Ca8Si12O30 (OH) 4·7H2O) was hydrothermally prepared in a stirred suspension at 180°Cusing mechanochemically treated starting mixtures of lime and amorphous precipitated silica at the theoretical Ca/Si ratios of 0.67 for gyrolite and 0.50 for the Zphase. The starting materials were treated by planetary ball milling for 15 min to 8 h at room temperature. With increased milling time, Ca (OH) 2reacted with silica to make a C-S-H like phase having a broad XRD peak centered at 0.30 nm. The C-S-H like phase contained a partly sheet-like silicate anion structure. Using the mechanochemically prepared mixture, with a Ca/Si=0.50 the hydrothermal reaction sequence is mechanochemically formed C-S-H→Assarsson's Z-phase→gyrolite and with a Ca/Si=0.67 mechanochemically formed C-S-H→gyrolite. However, using the mixtures at Ca/Si=0-67 without milling, the sequence is CaO+silica→hydrothermally formed C-S-H→gyrolite.
The fixation of carbon dioxide and calcification for calcium carbonate from waste concrete were investigated by incubating coccolithophorid algae (Gephyrocapsa oceanica) in seawater with Ca (HCO3) 2 solution which was dissolved excess calcium ion by streaming carbon dioxide through seawater with nutritive salts. This process was more effective to soft chemical reaction utilizing nature energy for resource recycling of waste concrete. Cell concentration of coccolithophorid algae and amount of fixed calcium carbonate as coccolith were determined by meaning optical microscope, scanning electron microscope and elementary analysis. The optimums for growing of Gephyrocapsa oceanica in seawater with nutritive salts were pH of 8.1-8.5, cell concentration of 40-60×104 cell·cm-3 and light/dark cycle of 12 h/12 h. The concentration of carbon dioxide passed through the seawater for dissolving waste concrete was effective at 5-20 vol%. Utilization of seawater with together nutritive salts and excess calcium ion was promoted growth of coccolith on surface of Gephyrocapsa oceanica and number of coccoloth pieces. This result was caused by dissolving excess amount of calcium ion in the seawater.
Silicate containing HAp (SiHAp) with various Si content, composition and with or without trace metallic elements were synthesized by wet method adding mixed solution of phosphoric acid-sodium silicate to Ca (OH) 2 slurry. Precipitate showed XRD pattern similar to low crystallinity HAp, and other crystalline phase like raw materials were not shown. It was found that Si exits as SiO44- ion in crystal structure from composition analysis, FT-IR, and so on. Thus SiHAp with large specific surface area could be synthesized by wet method which can product material inexpensively. The lattice constant of SiHAp was different from that of HAp, both a axis and c axis very expanded comparing with that of HAp. Furthermore, it was found that introducing of SiO44-ion to HAp structure arise CO2adsorption ability.
Several industrial and domestic waste products were used as raw materials for the production of inexpensive SiC. The waste products used as a carbon source were rice hulls, wheat hulls, weekly magazines, newspaper, copy paper, and paper milk cartons. As the Si source, silicon powder produced during the silicon wafer fabrication process was used. The carbon sources were carbonized by firing in a reducing atmosphere, and carbonized rice hulls were found to have the highest concentration of Si. The carbonized wastes were mixed with silicon powder and fired at high temperatures, successfully producing SiC. The products of rice hulls and silicon after firing at very high temperatures were almost identical to natural graphite and silicon systems, respectively.
The aim of this report is to describe a process for the recovery of nickel component in fly ash derived from oil burning. The optimum conditions for leaching nickel component from the fly ash and for recovering the nickel ions without accompanying magnesium ions by means of a solvent extraction method were studied. The results are summarized in the following. Aqueous ammonia solution was used as the most suitable lixiviant for leaching nickel ions from fly ash derived from oil burning which included a large amount of sulfate component. Versatic acid was used in the organic phase of the solvent extraction method, with the advantage that kerosene, including various kinds of aromatic compounds, could be used as a diluent. Nickel ions in the filtrate were successfully extracted by controlling the solution's pH in order to avoid the extraction of magnesium ions. A nickel sulfate solution of ion-free magnesium was obtained by a stripping process in which organic phase loaded nickel ions were washed with diluted sulfuric acid prior to the stripping process, even if magnesium ions would be extracted in the extraction process in spite of the controlled pH.