Decommissioning a phosphoric acid production plant: a radiological protection case study.

During a preliminary survey at the area of an abandoned fertilizer plant, increased levels of radioactivity were measured at places, buildings, constructions and materials. The extent of the contamination was determined and the affected areas were characterized as controlled areas. After the quantitative and qualitative determination of the contaminated materials, the decontamination was planned and performed step by step: the contaminated materials were categorized according to their physical characteristics (scrap metals, plastic pipes, scales and residues, building materials, etc) and according to their level of radioactivity. Depending on the material type, different decontamination and disposal options were proposed; the most appropriate technique was chosen taking into account apart from technical issues, the legal framework, radiation protection issues, the opinion of the local authorities involved as well as the owner's wish. After taking away the biggest amount of the contaminated materials, an iterative process consisting of surveys and decontamination actions was performed in order to remove the residual traces of contamination from the area. During the final survey, no residual surface contamination was detected; some sparsely distributed low level contaminated materials deeply immersed into the soil were found and removed.

Processing of metallurgical residues by flotation - bench-scale studies on two industrial products.

Resource recovery from two metallurgical residues by flotation was investigated applying an electrostatic model to select initial conditions. The first, a sulphation roast/water leach residue, was processed to float lead sulphate, comparing dodecylamine and xanthate collectors. From the second, a neutralization residue, gypsum, was recovered by reverse flotation of ferric hydroxide, comparing oleate and sulphonate collectors. In both cases, further upgrading by acid leaching was considered.

High-strength dental gypsum prepared by cold isostatic pressing.

Powder of a dental plaster (Moldabaster, Bayer) was compacted by cold isostatic pressing (CIP) at 300 MPa for 10 min and immersed in water for 1 h. The compressive strength of the CIP-processed material was compared with that of conventionally processed material. The green block of plaster before water immersion was carvable with a green density and green strength of 50% and 5 MPa, respectively. The compressive strength of the CIP-processed gypsum after 24 h was three times higher than that of conventionally processed, 103 compared with 29 MPa, and the microhardness (Vickers hardness number, VHN) of CIP-processed materials was 40 compared with 12 VHN. An increase of density was also recorded. It seems that the CIP process produced a dense and pore-free gypsum with a composite-like structure. The high-strength gypsum processed by CIP may extend the applications of this material in the medical field as implant materials.

Obtención de yeso piedra a escala de laboratorios / Attainment of hard plaster at laboratory level

Se reporta un tecnología de obtención de yeso piedra a escala de laboratorio para fines estomatológicos, partiendo de sulfato de calcio dihidratado representativo de 2 yacimientos cubanos y variando las condiones de calcinación. Se comprobó que más del 90 % en peso de las patículas deben tener un tamaño menor de 75 *m y que el producto final obtenido, con las muestras de ambos yacimientos, cumplía con la norma de calidad de la Asociación Dental Americana

Obtención de yeso piedra a escala de laboratorios / Attainent of hard plaster at laboratory level

Se reporta un tecnología de obtención de yeso piedra a escala de laboratorio para fines estomatológicos, partiendo de sulfato de calcio dihidratado representativo de 2 yacimientos cubanos y variando las condiones de calcinación. Se comprobó que más del 90

en peso de las patículas deben tener un tamaño menor de 75 *m y que el producto final obtenido, con las muestras de ambos yacimientos, cumplía con la norma de calidad de la Asociación Dental Americana