What Is HREE Ionic Adsorption Clay?

HREE Ionic Adsorption Clay, or Regolith Clay, is a type of rare earth element (REE) deposit formed through prolonged weathering of REE-rich volcanic and metamorphic rocks. These deposits are particularly interesting to mining industries due to their potential for extracting valuable rare earth elements from clays1. Let’s explore the key aspects of these deposits:

  1. Formation Process:
    • Intense magmatic activity during the Yanshanian (199.6–65.5 Ma) and Caledonian periods (542–359.2 Ma) provided the material basis for Regolith Clay formation in South China.
    • The regolith profile (0–8 m) in areas like Maofeng Mountain, Guangzhou city, contains high concentrations of REE.
    • The completely weathered layer (B1, B2, and B3 horizons) at depths of 2.5–4.5 m exhibits significant REE enrichment (849–2391 mg kg⁻¹).
    • Soil pH, the presence of kaolinite and halloysite, and metamorphic rock permeability influence the position of REE enrichment.
  2. REE Enrichment Mechanisms:
    • In the REE-enriched horizon (2–8 m), ion-exchangeable fractions host most of the REE (representing 79% of the total REE).
    • Fe–Mn (oxyhydr)oxides play a crucial role in REE enrichment, with the reducible fraction containing up to 21% of the total REE.
    • LREE (light rare earth elements) enrichment occurs in the reducible fraction, likely due to preferential release from LREE-bearing minerals (such as monazite) and subsequent scavenging by Fe–Mn (oxyhydr)oxides.
    • Positive Ce anomalies (Ce/Ce*: 10) are found in the reducible fraction, resulting from the oxidation of trivalent Ce by Fe–Mn (oxyhydr)oxides to cerianite (CeO₂).
  3. Implications:
    • Understanding the enrichment and fractionation of REE in Regolith Clay deposits contributes to our knowledge of ion adsorption-type rare earth deposits (IADs) in South China.

In summary, HREE Ionic Adsorption Clay represents a valuable resource for rare earth elements, and its geochemical patterns and mechanisms continue to be a subject of scientific exploration1