Remediation of Contaminated Soil with Radium-226 and 228 by Various Methods

Abstract

The most important radionuclides are 226Ra and 228Ra in oil and gas extraction industries due to their radiotoxicity and relatively long half-lives that affect the workers, the public surroundings, and the environment. These extraction activities accumulate naturally occurring radioactive material (NORM) due to the existence of the natural radionuclides in crude oil causing environmental contamination with these radionuclides (226Ra and 228Ra) and their progenies. This research aims to remediate the contaminated soil with these radionuclides by two methods namely mechanical separation and chemical treatment. The first technique is a physical separation of particle size of soil to screen the contaminated soil and evaluate the feasibility of particle size separation. The obtained fractions ranged from less than 37 µm (400 mesh) to higher than 900 µm (20 mesh) diameter of particle size as seven fractions. The results show that 226Ra and 228Ra activity concentrations vary from fraction to fraction. The greatest weight percent in the -900 to +600μm fraction, was 42.3% and the highest levels of activity concentration of 226Ra and 228Ra are concentrated in fine particle size cut (≤37.5μm). The second technique is the batch chemical washing of contaminated soil using the sequential chemical leaching method to extract radium isotopes from the contaminated soil, which is conducted in four successive steps. Five parameters were studied to obtain the best removal efficiency (R%) of 226Ra and 228Ra at optimum conditions for the leaching process; type of solvent, molarity concentration of the solvents, temperature of medium, contact time, and the number of treatment stages. Where, HNO3, HCl, H2SO4, C2H4O2, Na2EDTA, and C₆H₈O₇ were used in the chemical washing. In sequential extraction, the most effective solvents were found to be 1M acetic acid (C2H4O2) with 5:1 ml/g a liquid-to-solid ratio at a temperature of 40˚C, and 2-hour contact time. In the second stage of treatment, it is found that washing the contaminated soil with 0.1M Ethylenediaminetetraacetic disodium (EDTA Na2) after washing with 1M acetic acid (C2H4O2) to be the most effective solvent at the optimum mention conditions, where 94.3% and 93.4% of 226Ra and 228Ra, were removed to the aqueous phase respectively.