Immobilization of Eu and Ho from synthetic acid mine drainage by precipitation with Fe and Al (hydr)oxides

Alumina inhibits pyrite oxidative dissolution by regulating solid film passivation layer and S, Fe, and Al speciation transformation

The oxidation of pyrite results in the formation of a solid film passivation layer on its surface. This layer effectively hinders the direct interaction between H2O, O2, and the pyrite surface, thereby impeding the oxidation dissolution of pyrite. There are few studies on whether alumina (Al2O3), a common aluminum-containing oxide, affects the formation of a solid film passivation layer on the surface of pyrite and inhibits the oxidation dissolution of pyrite. This research investigates the impact of Al2O3 incorporation on the speciation transformation of S, Fe, and Al on the surface of pyrite during oxygen pyrite process. The oxidation of pyrite followed the "polysulfide-thiosulfate" complex oxidation pathway. When <1.5 g/L Al2O3 was introduced, it increase pyrite oxidation, whereas ≥1.5 g/L Al2O3 prevented pyrite oxidation. The process of Al2O3 dissolution results in the consumption of H+ and the subsequent release of Al3+. This, in turn, facilitates the hydrolysis of Fe3+ and Al3+ to generate a secondary mineral layer on the pyrite surface. As a result of the accumulation of S promotes the formation of polysulfide chemical (FeSn) or iron deficiency sulfide (Fe1-xS), resulting in the formation of a solid film passivation layer composed of sulfur film and secondary mineral layer. The results demonstrated that Al2O3 can promote the formation of a solid film passivation layer on the surface of pyrite, which has significant implications for controlling the oxidation dissolution process of pyrite and offers a new perspective for the source control of acid mine drainage.

Distribution and source determination of rare earth elements in sediment collected from the continental shelf off Hainan Island, China

Contents of rare earth elements (REEs), major elements, and the total organic carbon (TOC) were determined for 152 surface sediment samples collected from the continental shelf off Hainan Island (CSHI). From high to low, the average contents of REEs were as follows: Ce > La > Nd > Pr > Sm > Gd > Dy > Er > Yb > Eu > Ho > Tb > Tm > Tm. The LREEs in the south are more abundant than in the north, which is shown by the higher LREE/HREE values in south than in the north. This resulted higher values for the LREE/HREE ratio in the south than in the north. The mean enrichment factor (EF) could be arranged from highest to lowest as follows: Tm > Sm > Pr > Er > La > Lu > Ce > Tb > Eu > Nd > Yb > Gd > Ho > Dy. The EF indicates that pollution as a result of human activity was more serious in the southeast of the study area than in the north. The factors affecting the REE concentrations in this area include naturally occurring minerals and industrial pollution. Based on the spatial variation of upper continental crust (UCC)-normalized REE concentrations, the CSHI was classified into three geochemical provinces. The sediment of province I was controlled by the Red and Pearl rivers. The composition of the province II is mainly controlled by the Red River and the Pearl River, although some sediments have originated from the South China Sea Island. Province III sediments mainly originated from sources on Hainan Island.

The role of iron in the rare earth elements and uranium scavenging by Fe-Al-precipitates in acid mine drainage

The scavenging of soluble metals by iron (Fe) and aluminium (Al) oxyhydroxides is a natural process that occurs in acid mine drainage (AMD). This phenomenon is relevant to the immobilization, transport, and recovery of important natural resources such as rare earth elements (REE) and uranium (U). Furthermore, understanding the players and the reactions that govern the scavenging of REE and U by Fe and Al oxyhydroxides in aqueous systems is fundamental for natural and engineering sciences and for environmental management. In this scenario, the current work investigated the role of iron in the co-precipitation of REE and U when treating effluents by pH neutralization in an AMD system located in Brazil. The research employed water sampling, co-precipitation batch experiments, sequential extraction, X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy. The results revealed that the presence and the amount of Fe in the initial solution can influence the REE removal efficiency positively. The effect of the addition of Fe over the REE removal efficiency was irrelevant when the pH of the AMD was raised to values equal to 7-8. The scavenging of U was not influenced by the addition of Fe to the AMD. The sequential extraction results showed that precipitates containing higher amounts of Fe tend to be less labile. The ⁵⁷Fe Mössbauer spectra revealed that the REE can occupy iron sites in the structure of the amorphous precipitates. The findings of the current study can be extrapolated to other AMD systems and contribute to the development of novel REE recovery and hydrometallurgical techniques.

Baseline of distribution and origin of Rare Earth Elements in marine sediment of the coastal area of the Eastern Gulf of Tigullio (Ligurian Sea, North-West Italy)

A study on the Rare Earth Element (REE) distribution in the bottom sediments of the Gulf of Tigullio (north-west Italy) was conducted. The results constitute a baseline for this zone of the Ligurian Sea and enabled the obtaining of valuable information on the origin and transport of sediments in the gulf. The distribution of REEs is controlled by phosphates, mainly monazite, and is generally homogeneous in the study area, reflecting the homogeneous distribution of the minerals. Some differences in REE and Sc distribution allow us to identify two sub-basins (Entella and Gromolo torrent sub-basins) characterised by slightly different geological frameworks. The "hat-shaped" observed patterns seem to indicate an overprinting of the original REE patterns due to exchanges between phosphates and seawater. REEs seem to be related with the rocks outcropping in the area, although an indirect effect of anthropic activity could be seen near a fish farm.

Mine drainage: Treatment technologies and rare earth elements

The recent research and development on mine drainage published in 2018 was summarized in this annual review. In particular, this review was focused on two main aspects of mine drainage: (a) advances in treatment technologies and (b) rare earth elements in mine drainage and its recovery. The first section covers passive treatment technologies and active treatment options, including physiochemical treatment and biological treatment. The second section includes the characterization of rare earth elements in mine drainage and recovery technologies. Due to the importance of rare earth elements and the growing interest in their recovery from mine drainage, rare earth elements are reported as a separate section for the first time in this review. PRACTITIONER POINTS: Advances in treatment technologies for mine drainage are reviewed. Rare earth elements in mine drainage and its recovery are summarized. Reviewed technologies include passive, active, advanced and novel processes.