The speciation of inorganic arsenic compounds produced in pulverized coal combustion was investigated in a bench-scale study conducted under fuel-lean combustion conditions. Results suggest that at temperatures of 850-1100 K, and in the absence of particulate, arsenic initially condenses as As2C>3 rather than the thermodynamically favored AS2O5. Synthetic fly ash in the form of uniform 0.25 pm spherical silica particles produced by sol-gel methods, added to the experimental system to simulate the presence of combustion-derived fly ash, did not affect arsenic speciation, nor did doping of the silica particles with small amounts of calcium. As(V) was only observed at these temperatures when calcium was added to the system as calcium acetate, producing a reactive calcium oxide fume and leading to the formation of calcium arsenate. From these results, it was concluded that the formation of arsenic(V) in combustion systems requires either the oxidation of AS2O3, which appears to be a kinetically limited process, or the presence of reactive calcium compounds. Additional experiments conducted with calcium silicate in an isothermal tube furnace suggested that calcium in silicates is capable of reacting with arsenic under long (order minutes) reaction time conditions. The apparent ability of calcium silicate particles to capture arsenic under idealized conditions suggests that calcium embedded in silicate fly ash may be capable of forming calcium arsenate, but the extent of this reaction on the time scales of a pulverized coal combustor or waste incinerator remains unclear.

No abstract

No abstract

Radioactive mercury waste constitutes a significant challenge, as no approved disposal concept yet exists for such waste in Germany. This work describes a decontamination and measurement procedure for a possible clearance of mercury from nuclear facilities and release into reuse or conventional hazardous waste disposal to reduce the amount of mercury in a nuclear repository. The measurement setup and procedure were developed and evaluated including Monte-Carlo N-Particle® Transport Code (MCNP® and Monte Carlo N-Particle® are registered trademarks owned by Los Alamos National Security, LLC, manager and operator of Los Alamos National Laboratory, (Werner 2018, Werner 2017)), simulations to ensure conservative assumptions during the measurements. Results from decontaminated mercury samples show that a clearance pursuant to the German regulations would be feasible.