Removal of radium from groundwater using a modified bauxite refinery residue

Radium (Ra) removal by an unconventional sorbent, a modified bauxite refinery residue (MBRR), is investigated for a groundwater extracted in Missouri, USA. The MBRR treatment causes substantial reductions of both gross α and combined ^226/228Ra activities from 0.955 ± 0.005 and 0.66 ± 0.005 Bq L⁻¹ to below detection limits (0.037 Bq L⁻¹ or 1 pCi L⁻¹). Column breakthrough occurs at 0.555 Bq L⁻¹ for gross α and 0.185 Bq L⁻¹ for combined ^226/228Ra (15 and 5 pCi L⁻¹; USEPA's maximum contaminant levels) after 54 and 40 d run time, respectively. At 84 d the MBRR media continues to remove 24.3% of raw water gross α and 39.7% of the combined ^226/228Ra. The treatment effluent has an initial pH of 10.9, outside the USEPA guides (6.5–8.5); this may be readily mitigated by posttreatment acid injection, or by raw water blending. The MBRR simultaneously removes other potentially hazardous trace elements (e.g., Cu, Zn, and Fe) to extremely low concentrations. In addition, toxicity characteristic leaching procedure testing of spent MBRR suggests that metals are bound tightly, such that it is nonhazardous, permitting cost-effective disposal to landfill without special confinement or storage. Consequently, MBRR may be utilized as an alternative adsorbent for treating Ra-contaminated groundwater.