PRECIPITATION OF COLLOID SILICA FROM HYDROTHERMAL SEPARATE BY COAGULANTS ADDITION ( KAMCHATKA , RUSSIA )
We have carried out the experiments on coagulation and precipitation of silica from the separate of Verkhne-Mutnovsky geothermal electric power plant (Mutnovskoe hydrothermal field). Silica precipitation from the water solution was conducted in two ways: by adding slaked lime CaO and by electrocoagulation treatment on aluminium electrodes. Silica precipitation with addition of slaked lime was carried out under laboratory conditions at the temperature of 20 and 96 °C. Сolloid and monomeric silica concentrations, solution pH, flakes sizes and physical-chemical properties of material precipitated with different quantities of added lime were determined. We also carried out series of experiments on solution treatment of mixed type: addition lime with freshly precipitated flakes, and addition lime with sea water. In the experiments on electric coagulation, current intensity and distance between electrodes were changed. Dependence of silica concentration on treatment duration was studied. Quantities of electric energy and anode aluminium consumed for reducing of silica concentration to a certain level were obtained. The results of our experiments can be used for developing of technological scheme of silica precipitation and utilization optimal for Verkhne-Mutnovsky geothermal electric power plant.
STUDY OF THE AMORPHOUS SILICA SCALES FORMATION AT THE MUTNOVSKOE HYDROTHERMAL FIELD (RUSSIA)
Formation of the amorphous silica solid scales in wells, separators, pipes and heat exchangers is the essential problem that makes difficult wide usage of geothermal resources. Various types of amorphous silica were selected at the Mutnovskoe field and their silicate, X-ray diffraction and thermochemical analyses were done. The possibility of disposal brine treatment by alkali and acid before reinjection was studied under conditions of VerkhneMutnovskaya geothermal electric power station by the numerical modeling study of the chemical equilibrium in the multicomponent solution. Data of the test on determining the rate of the silica scales growth in heat exchanger and results of the electrochemical treatment of hydrothermal solution are given. Results of this study can be used in technology of geothermal silica precipitation which is considered as a by-product.
Phase characterisation of simulated high burn-up UO2 fuel
Abstract To determine the lattice constant variation with burn-up and the oxidation behaviour at high temperatures, simulated UO2-spent fuels with burn-ups up to 200 GWd tM−1 were prepared by cold pressing and sintering and characterised by X-ray diffraction analysis and thermogravimetry. The fcc-lattice parameter of the sintered samples determined at room temperature, showed a continuous decrease with the simulated burn-up. During oxidation the conversion of the simulated fuels to the (U,FP)4O9 and (U,FP)3O8-type phases was strongly delayed when the simulated burn-up exceeded 80 GWd tM−1. Also, at high burn-ups (>100 GWd tM−1), large fractions of the (U,FP)4O9-type phase remained untransformed to (U,FP)3O8 after prolonged exposure to air at 950–1000°C. This suggests a marked widening of the (U,FP)4O9-phase field when the amount of substituted uranium atoms exceeds values of about 8%.