Arsenic is a major contaminant in the nonferrous extractive metallurgy. In the past 20 years, many studies have shown that it can be precipitated as relatively stable crystalline scorodite (FeAsO 4 • 2H 2 O) by precipitation under ambient or elevated pressures. In the present study, an extensive program of scorodite precipitation tests under ambient pressure has shown that the rate of scorodite formation increases dramatically by a small increase in temperature from 85 °C to 100 °C. The beneficial effects of temperature are attributed to the higher thermodynamic stability of scorodite at elevated temperatures, but also to higher rates of secondary nuclei formation and crystal growth. In any case, irrespective of the precipitation temperature, the leachability of all scorodite precipitates observed in toxicity characterization leaching procedure (TCLP) tests is below 5 mg/L As. Another parameter examined in this study was seeding. It was observed that the higher the initial concentration of seed, the faster the precipitation. Precipitation of well-crystallized scorodite can be effected equally well on heterogeneous seed such as hematite (Fe 2 O 3 ) or gypsum (CaSO 4 • 2H 2 O) added externally or formed in situ.
OverviewIn the past four years, a new process has been developed at McGill University for the immobilization of arsenic from metallurgical effluents and flue dusts by the controlled precipitation of scorodite under atmosphericpressure conditions. So far, the process has been successfully tested in the laboratory with chloride and sulfate solutions containing arsenic and with As 2 O 3 smelter flue dusts. It has been also tested with equal success at a copper smelter with industrial arsenic-containing sulfate effluents.
This work shows, for the first time, the critical influence of pressure during the hot sintering stage on the ionic conductivity of the lithium super ionic conductor Li1.5Al0.5Ge1.5(PO4)3. A hot press method is developed to obtain high ionic conductivities at the significantly decreased densification temperature of only 650 °C by applying pressure (56 MPa). Considering the possible initiation of undesirable decomposition reactions when cathode materials are annealed at high temperature (typically ≥700 °C), the use of high pressure at 650 °C can significantly limit the formation of degradation by‐products. This study determines the criteria required to optimize the pressure and temperature parameters for enhancing the total ionic conductivity. Finally, this study reports an all solid‐state battery based on a LiFePO4 olivine cathode prepared at 650 °C showing very good Li‐intercalation/deintercalation performance. Good ionic interfacial contact is achieved without using polymer and liquid electrolyte.
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