Coal mine drainage (CMD) and associated metal-rich precipitates have recently been proposed as unconventional sources of rare earth elements (REEs). However, the potential occurrence of radium (Ra), a known carcinogen, with the REE-bearing phases has not been investigated. We hypothesized that Ra may occur in solids that are precipitated from CMD as a “radiobarite” solid solution ((Ba,Sr,Ra)SO) and/or adsorbed with hydrous metal oxides. REEs have been documented to sorb or co-precipitate with iron (Fe), manganese (Mn), and aluminum (Al) oxyhydroxide in CMD solids. Likewise, Ra has been documented to sorb to hydrous Fe and Mn oxides especially where sulfate (SO) and/or barium (Ba) concentrations are insufficient to precipitate radiobarite. Thus, we conducted the first-ever survey of Ra concentrations in corresponding CMD water and solid samples in the United States. Samples were analyzed from 4 untreated and 9 treated CMD sites in both the bituminous and anthracite coal regions of Pennsylvania across a range of pH and SO concentrations. The dissolved Ra in CMD was relatively low (<0.5 Bq/L), consistent with radiobarite solubility; however, CMD solids were largely composed of amorphous Fe, Al, and Mn oxyhydroxide and silicate minerals. Ra was associated with Mn-enriched CMD solids, upwards of 875 Bq/kg. Total REE + yttrium (Y) content in the CMD solids was enriched upwards of 3600 mg/kg and was significantly correlated with Al content. These preliminary results suggest that REE extraction may target Al-rich solids to avoid Ra in Mn-rich solids.

中文翻译：

---

煤矿排水和伴生沉淀物中镭和稀土元素浓度的评估


最近，煤矿排水（CMD）和相关的富含金属沉淀物被提议作为稀土元素（REE）的非常规来源。然而，尚未研究含稀土相的已知致癌物镭 (Ra) 的潜在存在情况。我们假设 Ra 可能以“放射性重晶石”固溶体 ((Ba,Sr,Ra)SO) 的形式从 CMD 中沉淀出来和/或被水合金属氧化物吸附。据记载，稀土元素可以与 CMD 固体中的铁 (Fe)、锰 (Mn) 和羟基氧化铝 (Al) 吸附或共沉淀。同样，Ra 已被证明会吸附到水合 Fe 和 Mn 氧化物上，特别是在硫酸盐 (SO) 和/或钡 (Ba) 浓度不足以沉淀放射性重晶石的情况下。因此，我们对美国相应的 CMD 水和固体样品中的 Ra 浓度进行了首次调查。对宾夕法尼亚州烟煤和无烟煤地区 4 个未经处理和 9 个经过处理的 CMD 地点的样品进行了分析，涵盖了一系列 pH 和 SO 浓度。 CMD 中溶解的 Ra 相对较低（<0.5 Bq/L），与放射性重晶石的溶解度一致；然而，CMD 固体主要由无定形 Fe、Al 和 Mn 羟基氧化物以及硅酸盐矿物组成。 Ra 与富锰 CMD 固体相关，最高可达 875 Bq/kg。 CMD 固体中的总 REE + 钇 (Y) 含量富集至 3600 mg/kg，并且与 Al 含量显着相关。这些初步结果表明，稀土元素提取可能针对富铝固体，以避免富锰固体中的 Ra。