Estimation of 226Ra and 228Ra Content Using Various Types of Sorbents and Their Distribution in the Surface Layer of the Black Sea

Ol'ga N Kozlovskaia; Iuliia G Shibetskaia; Nikolay A Bezhin; Ivan G Tananaev

doi:10.3390/ma16051935

Estimation of ²²⁶Ra and ²²⁸Ra Content Using Various Types of Sorbents and Their Distribution in the Surface Layer of the Black Sea

Materials (Basel). 2023 Feb 26;16(5):1935. doi: 10.3390/ma16051935.

Authors

Ol'ga N Kozlovskaia^{1

2}, Iuliia G Shibetskaia^{1

2}, Nikolay A Bezhin^{1

2}, Ivan G Tananaev^{2

3

4}

Affiliations

¹ Department of Biogeochemistry, Marine Hydrophysical Institute, Russian Academy of Sciences (MHI RAS), Kapitanskaya Str., 2, 299011 Sevastopol, Russia.
² Department of Chemistry and Chemical Engineering, Sevastopol State University, Universitetskaya Str., 33, 299053 Sevastopol, Russia.
³ Radiochemistry Laboratory, Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences (GEOKHI RAS), Kosygin St., 19, 119991 Moscow, Russia.
⁴ Department of Nuclear Technology, Far Eastern Federal University, Sukhanov Str., 8, 690091 Vladivostok, Russia.

Abstract

Radium isotopes have traditionally been used as tracers of surface and underground fresh waters in land-ocean interactions. The concentration of these isotopes is most effective on sorbents containing mixed oxides of manganese. During the 116 RV Professor Vodyanitsky cruise (22 April-17 May 2021), a study about the possibility and efficiency of ²²⁶Ra and ²²⁸Ra recovery from seawater using various types of sorbents was conducted. The influence of seawater flow rate on the sorption of ²²⁶Ra and ²²⁸Ra isotopes was estimated. It was indicated that the Modix, DMM, PAN-MnO₂, and CRM-Sr sorbents show the best sorption efficiency at a flow rate of 4-8 column volumes per minute. Additionally, the distribution of biogenic elements (dissolved inorganic phosphorus (DIP), silicic acid, and the sum of nitrates and nitrites), salinity, and ²²⁶Ra and ²²⁸Ra isotopes was studied in the surface layer of the Black Sea in April-May 2021. Correlation dependencies between the concentration of long-lived radium isotopes and salinity are defined for various areas of the Black Sea. Two processes control the dependence of radium isotope concentration on salinity: conservative mixing of riverine and marine end members and desorption of long-lived radium isotopes when river particulate matter meets saline seawater. Despite the high long-lived radium isotope concentration in freshwater in comparison with that in seawater, their content near the Caucasus shore is lower mainly because riverine waters meet with a great open seawater body with a low content of these radionuclides, and radium desorption processes take place in an offshore area. The ²²⁸Ra/²²⁶Ra ratio derived from our data displays freshwater inflow spreading over not only the coastal region, but also the deep-sea region. The lowered concentration of the main biogenic elements corresponds to high-temperature fields because of their intensive uptake by phytoplankton. Therefore, nutrients coupled with long-lived radium isotopes trace the hydrological and biogeochemical peculiarities of the studied region.

Keywords: 226Ra; 228Ra; PAN-MnO2; nutrients; seawater; sorbents; sorption.

Abstract

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