Lichen specie Canoparmelia texana as bioindicator of environmental impact from the phosphate fertilizer industry of São Paulo,Brazil

The Brazilian phosphate industry is the sixth worldwide producer of phosphate rock concentrate generating phosphoric acid, fertilizers, intermediates for fertilizers and other products. Two of the most important of these industries are both located in the city of Cubatão—São Paulo, Brazil, and they are responsible for the production of P₂O₅, generating a residue known as phosphogypsum. The raw material, phosphate rock and products are commonly transported to the industrial complex by a railroad line and present in their composition natural radionuclides from the U and Th series and rare earth elements. Lichens have been used for monitoring atmospheric pollution and radiological contamination for a long time and have proven to be an important tool. This paper aims to highlight the use of the lichen specie Canoparmelia texana (family Parmeliacea) as a bioindicator of atmospheric pollution by the natural radionuclides from the U and Th series and RREs due to the operation of these industries and the storage of their residue in the open air. Samples of these lichen specie were collected in the vicinity of the industries and the railroad. The radionuclides ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were measured by alpha and beta counting, after radiochemical separation, and ²³⁸U, ²³²Th as well as REEs were determined by instrumental neutron activation analysis. The results showed that the lichens present the same fingerprint as the phosphate rock and phosphogypsum, furthermore the cluster analysis of the results showed that the lichen samples collected near to the railroad line presented the highest values for all the elements studied.     

Treatment of phosphogypsum waste using suitable organic extractants

Phosphogypsum (PG) is a residue of the phosphate fertilizer industry that has relatively high concentrations of harmful radioactive materials. The reduction in concentration of the radionuclides from PG was investigated. The removal process is based on leaching of radionuclides using suitable organic extractants. The studied radionuclides were ²²⁶Ra, ²¹⁰Pb, ²³⁸U and ⁴⁰K. The factors affect the leaching process such as type of leaching materials, contact time, concentration of the desired solvent, liquid to solid ratio, and temperature were studied. Based on the experimental results, about 71.1, 76.4, 62.4, and 75.7% of ²²⁶Ra, ²¹⁰Pb, ²³⁸U and ⁴⁰K respectively were successfully removed from the PG. The reduction in the concentration of radionuclides was accompanied by reduction in the concentration of rare earth elements (∑REE) equals to 69.8%. Using the desired organic extractant under optimum conditions for treatment of the PG waste leads to obtain a decontaminated product that can be safely used in many industrial applications.     

Identification and determination of natural radioactive impurities in rare earth chlorides

²²⁷Ac,²²⁸Th,²²⁶Ra,²¹⁰Po and²¹⁰Pb can be present at rare earth chlorides. A radiochemical procedure is presented for the identification and determination of natural radioactive impurities in rare earth chlorides. The determination limits for these radionuclides were 1.5·10^–4 to 3·10^–1 Bq/g. The relative standard deviations for determining 10^–2 Bq/g radionuclides were usually less than ±7%.     

Leaching of uranium,radium and thorium from vertisol soil by ground water

Shallow land burial is routinely used for the disposal of low-level radioactive waste. Natural processes causing leaching of radionuclides can lead to contamination of surrounding ground water and soil by the radionuclides. The comparative leachability of radionuclides U_(nat), ²²⁶Ra, ²²⁸Ra and Th_(nat) from the soil of a radioactive waste disposal site, by ground water was evaluated. The probability of leaching was obtained in the following order Ra (≈77%) > U (≈40%) > Th (≈20%). Observed ratios (OR) were calculated to correlate leachability of radionuclides to that of major cations Ca²⁺ and Mg²⁺. The leaching of the radionuclides was seen to be dependent on Ca²⁺ and SO₄²⁻ leached from the soil. This study provides sitespecific leachability of radionuclides, that can be used as indicator of the tendency for migration or retention in soil. It can play an important role during an unforeseen accident like breach of containment at the waste disposal site leading to contamination of soil and ground water and causing hazard to public via drinking water route.