Laboratory Enrichment of Radioactive Assemblages and Estimation of Thorium and Uranium Radioactivity in Fractions Separated from Placer Sands in Southeast Bangladesh

Abstract

The present study reports the likely first attempt of separating radioactive minerals for estimation of activity concentration in the beach placer sands of Bangladesh. Several sand samples from heavy mineral deposits located at the south-eastern coastal belt of Bangladesh were processed to physically upgrade their radioactivity concentrations using plant and laboratory equipment. Following some modified flow procedure, individual fractions were separated and investigated using gamma-ray spectrometry and powder-XRD analysis. The radioactivity measurements indicated contributions of the thorium and uranium radioactive series and of 40 K. The maximum values of 232 Th and 238 U, estimated from the radioactivity of 208 Tl and 234 Th in secular equilibrium, were found to be 152,000 and 63,300 Bq/kg, respectively. The fraction of the moderately conductive part in electric separation contained thorium predominantly, while that of the non-conductive part was found to be uranium rich. The present arrangement of the pilot plant cascade and the fine tuning of setting parameters were found to be effective and economic separation process of the radioactive minerals from placer sands in Bangladesh. Probable radiological impacts and extraction potentiality of such radioactive materials are also discussed.

Presence of uranium and thorium in zircon assemblages separated from beach sands of Cox’s Bazar, Bangladesh

“…Zircons of Bangladesh show some typical prismatic shape containing different types of inclusions, and transparent in cross polarized light, whereas some others are mostly subrounded and not as transparent as typical zircon grains. Inclusions in zircon grains may contain uranium whereas later types of grains sometimes include the mineral monazite (Sasaki et al, 2015) of which Th is a constituting element. Monazite grains are very fine and sometimes resembles with a variety of zircon.…”

“…Thorium concentration in the un-identified minerals of the zircon assemblages.Radioactivity in beach placers of Bangladesh are already reported quite high when properly separated from other non-radioactive fractions(Sasaki et al, 2015;Zaman et al, 2012). The main source of the radioactivity is coming from mostly monazite and zircon as suggested by those researches.…”

“…didn't let the commercial exploitation of those economic minerals. Hence, maximum economic value can be achieved if the radioactive materials can be extracted from these beach minerals (Sasaki et al, 2015). Therefore, the objective of the present study was to separate zircon from beach sand by the processes of specific gravity, magnetic and electric separations, to verify their presence by microscopic and X-ray Diffraction (XRD) technique, and to measure the concentrations of both uranium and thorium in zircon using Neutron Activation Analysis (NAA).…”

“…Zircon is also radioactive to some extent because it contains radioactive elements in its composition (Bazzari et al, 1986;Evans et al, 2005;Natarajan et al, 2012). However, there is very limited information about the quantification of radioactive elements (particularly U and Th) in zircon from Cox's Bazar except very recent findings from Sasaki et al (2015) and Zaman et al (2012).The presence of such radioactive elements in zircon or other minerals could hamper the mining attempt of heavy minerals in coastal areas. If anomalous radioactivity arises from zircon, it will create occupation hazards for mine workers.…”

Accumulation of heavy minerals in the eastern coast of the Gulf of Riga, south-western Estonia

“…At the Lemmeoja sites these laminations contain extremely high quantities of heavy minerals; so they could even be called placer deposits. Wave energy and gravitational processes (heavier minerals settle) in the open beaches are a driving force for accumulation (Komar & Wang, 1984;Sasaki et al, 2014).…”