P. M. B. Pillai

Dissolution characteristics of 226Ra from phosphogypsum

The paper presents the results of the dissolution characteristics of 226Ra from phosphogypsum, a by-product from phosphate fertilizer industries. Leachability of 226Ra in distilled water and rainwater have been examined under different leaching conditions such as contact time, solid:liquid ratio and simulating natural conditions. The concentration of 226Ra activity in the leachates ranged from 0.07 to 0.53 Bq l(-1). Study indicated that leaching of radium may be slow in field conditions near the phosphogypsum stock piles.

Studies on the Leaching of Radium and the emanation of radon from fertilizer process sludge

Abstract Radium-226 present in rock phosphate is carried to CaCO 3 , the main process waste sludge of the fertilizer industry. Disposal of the sludge in the environment enhances the radiation background in the area. Two states of adherence of radium in the sludge have been identified, one loosely bound and the other chemically exchanged. The loosely bound fraction accounts for nearly 40% of the total activity, as demonstrated by leaching studies. Laboratory experiments show that activity leach-out by infiltration of water through the sludge is low. Lateral seepage is found to cause extensive areal contamination due to dispersal of suspended solids in the vicinity of the disposal area. The rate of emanation of radon from the sludge is found to be high, a factor of 10 over the normal background emanation rate. The radiation field in the waste disposal area also shows enhancement, with levels 4–6 times higher than natural background.

An evaluation of radiation exposures in a tropical phosphogypsum disposal environment.

Environmental radiological aspects of phosphatic fertiliser production with particular reference to disposal of phosphogypsum at two sites in India are examined. Concentration of uranium and its decay products in the rock phosphate and products are presented. External gamma exposure and inhalation of radon and progeny are found to be the major routes of exposure to public in phosphogypsum disposal environment. An estimate of the committed effective dose to a representative person gives an average additional dose of 0.6 mSv annually in the study sites.

Occupational radiation exposure due to norm in a rare-earth compounds production facility

In India, rare-earth compounds are produced from the beach sand mineral monazite. Caustic digestion of the mineral followed by selective acid extraction is the method used to separate composite rare-earth fraction. The composite rare-earth chloride contains low levels of natural radionuclides and is the starting material for individual rare-earth compounds which have wide applications. Activity concentrations in composite rare-earth compounds such as chlorides, fluorides, carbonates and oxides of Ce, Nd, Pr, Sm, Gd, etc. are presented in this paper. The external gamma exposure rates and airborne activity due to thorium and thoron progeny in the occupational environment are studied. The activity levels in liquid effluent are presented. The potential individual occupational dose is estimated to be 1.9 mSv per annum.

Radiation exposure at the high background area at Manavalakurichi ― the changing trends

Abstract Large-scale surface mining and refilling of the mined areas with monazite-free tailings have reduced the external radiation fields by an order of magnitude, at some locations at the natural high background areas situated in the coastal regions of peninsular India. Significant reduction by a factor of 3 has been observed in the airborne activity due to lower emanation of thoron (220Rn) at the refilled areas. The thathched huts in the area are giving way to brick and concrete structures, thus radically altering the indoor exposures. The exposure due to gamma radiation from the external surroundings was reduced by a factor of 4 due to the shielding by the construction materials. 220 Rn levels as high as 420 Bq m −3 have been observed in some of the mud houses. Significant levels of 232 Th and 228 Ra were found in the urine samples collected from the adult residing in a village, situated in the high background area.