Radium-226 is considered one of the

Radium-226 is considered one of the most important uranium decay series radionuclides due to
its long half-life (1600 years) and radiological effects. It is one of the most toxic long-lived alphaemitters
present in the environment (Kozempel et al., 2015; Landsberger et al., 2013). 226Ra may
also be present in the environment in enhanced concentration due to activities of uranium mining,
phosphate ore processing, coal ash, water treatment, metal mining and processing, geothermal
energy production, and petroleum industry (Al-Masri et al., 2014; Al-Masri et al., 2002; Beddow
et al., 2006; Déjeant et al., 2014; IAEA, 2013; Othman and Al-Masri, 2007; Parmaksýz et al.,
2015).
The need for 226Ra in readily available soluble form is currently increased due to the high interest
in the research of radium chemistry and its uses in different applications such as the preparation
of calibration sources or as a target material in nuclear reaction studies (Kozempel et al., 2015).
In addition, more attention was focused on the environmental and health impacts of the
uncontrolled discharge of naturally occurring radionuclide materials (NORM) wastes, mainly
radium isotopes containing wastes (Al-Masri and Aba, 2005; Al-Masri and Haddad, 2012; Al-
Masri et al., 2014; Al Attar et al., 2014; El Afifi and Awwad, 2005; Hrichi et al., 2013; IAEA,
2004, 2013; Landsberger et al., 2013; Parmaksýz et al., 2015). Trials towards the treatment of
NORM wastes from many industries are still limited (Abdellah and Al-Masri, 2014; Attallah et
al., 2015; IAEA, 2013). The main form of radium in different solid waste is [226Ra]BaSO4
precipitate, which is insoluble in water, aqueous solutions of mineral acids, alkalis and organic
solvents (Attallah et al., 2015), while it can be dissolved in concentrated sulfuric and perchloric
acids (Lide, 2005).
In wet radiochemical analysis, 226Ra is co-precipitated quantitatively with Ba from acidic media
(H2SO4) as [226Ra]BaSO4 (Medley et al., 2015). Dissolution of [226Ra]BaSO4 is usually achieved
by the use of chelating agents such as EDTA (Ethylene-di-amine-tetra-acetic acid) or DTPA (Diethylene-
tri-amine-penta-acetic acid) (Jia and Jia, 2012; Kirby and Salutsky, 1964; Kuznetsov et
al., 2013). The use of these chelating agents may interfere with subsequent purification steps
prior to radioactivity measurement, which makes the method more expensive and time
consuming (Jia and Jia, 2012; Kuznetsov et al., 2013; Nour et al., 2004; Suarez-Navarro et al.,
3
2015). In addition, RaSO4/[226Ra]BaSO4 can be converted to soluble compounds by
carbonatization, fusion with alkali metal carbonates and reduction to sulfide in oxygen-free
atmosphere (Kozempel et al., 2015; Kuznetsov et al., 2013). Generally, most of the reported
methods for [226Ra]BaSO4 dissolution are expensive and time consuming because of the many
chemical steps involved and sometime unsafe, i.e. the high temperature used in the
carbonatization in a melt.
Due to high solubility of BaS, the reduction of sulfates into sulfide was investigated in several
studies (Bilal and Tributsch, 1998; Xu et al., 2013). Table 1 provides information on the variation
of solubility of some Ba and Ra compounds in water, at 20 °C. Tyson and Palmer (2009) studied
the reduction method for the detection of sulfur by flow-injection hydride generation. They used
a mixture of hydriodic acid, acetic acid and sodium hypophosphite under microwave irradiation;
around 80-90 % conversion of sulfate and sulfite into sulfide has been achieved.
Recently, another method was proposed by Kozempel et al. (2015) for the dissolution of
[226Ra]BaSO4 with Na2CO3 where microwave assisted processing with overpressure in a sealed
reactor was used.
This paper describes the development of a new procedure for total dissolution of
RaSO4/[226Ra]BaSO4 using NaNO2 as a reducing agent in acidic solution, at room temperature.
Various experimental conditions such as acid type, acid and reducing agent concentrations and
temperature were optimized. In addition, a procedure for Ra-Ba separation was also investigated.