Soil Rare Earth Elements in Afram Plain Ecosystems via Neutron Activation Analysis

Ebenezer Aquisman, Asare and Dickson, Abdul Wahab and Anita, Asamoah and Elsie Effah, Kaufmann and Rafeah, Wahi and Zainab, Ngaini and Dickson, Adomako and Joseph Richmond, Fianko (2025) Soil Rare Earth Elements in Afram Plain Ecosystems via Neutron Activation Analysis. Water, Air, & Soil Pollution, 237 (321). pp. 1-33. ISSN 1573-2932

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Abstract

This study characterizes rare earth element (REE) distributions in Afram Plain soil profiles using neutron activation analysis (NAA) combined with Bayesian Hierarchical Models (BHMs). Forty-eight samples from eight locations across seven soil types were analysed at the Ghana Research Reactor-1 using k₀-standardization. Mean total REE concentration was 728.6 mg/kg, substantially higher than regional comparisons, with an unusual HREE-enriched signature (ΣLREE/ΣHREE ≈0.6). Waterbody sediments showed highest accumulation (763.8 mg/kg), while Haplic Lixisols had highest La concentrations (64.10 mg/kg). The BHM identified depth and pH as the most clearly influential predictors of total REE concentrations, with REEs increasing with depth and accumulating preferentially under higher pH conditions. Soil-type effects, while allowing for group-level variability, showed 95% highest density intervals spanning zero for all soil types, indicating that distinguishing these effects requires larger sample sizes. Enrichment factors for HREEs (Tm, Yb, Lu) reached extremely high values (102 –103 ), warranting careful interpretation given potential normalization artifacts from variable iron content. Fractionation indices revealed persistent negative Ce anomalies and neutral to positive Eu anomalies across profiles. This study demonstrates the utility of combining NAA with BHM for transparent uncertainty quantification in environmental REE assessments, while acknowledging that mineralogical characterization is needed to explain the unusual HREE enrichment patterns.

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