Mineralogical and Chemical Characterization of Clay Minerals in Albania for Sustainable Soil Management

Abstract

Heavy metal contamination in soils poses serious ecological and food-chain risks, particularly in ultramafic landscapes where total and bioavailable nickel (Ni) concentrations are naturally high. This study investigated the mineralogical and chemical properties of clays derived from different parent materials to evaluate their capacity to immobilize Ni and reduce heavy metal toxicity to agricultural plants. Soil samples from two ultramafic regions (Rrajcë and Prrenjas) and one non-ultramafic site (Durres) were analyzed for texture, pH, organic matter, cation exchange capacity (CEC), and mineralogy (XRD). Smectite-dominated Prrenjas clay exhibited abundant interlayer and edge sorption sites, enabling rapid chemisorption and immobilization, with ~89% of Ni within 240 min when added to Rrajcë soil. In comparison, Durrës clay—containing only 30% smectite and dominated by illite, chlorite, kaolinite, and minor serpentine—immobilized only ~64%. These kinetic and mineralogical contrasts demonstrate that expansive smectite clay types (e.g., smectite), rather than total clay content, are the principal drivers of Ni adsorption capacity and reaction rates. A pot experiment further showed that amending Ni-rich Rrajcë soil with smectite-rich clay (1.07%–3.2%) significantly reduced Ni accumulation in alfalfa (Medicago sativa) by 20%–45%, accompanied by a 2.6%–16% decline in the plant-available fraction of soil Ni. These results highlight strong links between clay mineralogy, Ni bioavailability, and plant uptake. Overall, the findings provide new insights into Ni mobility in ultramafic soils and demonstrate that smectite-rich clay amendments represent an effective, low-cost, and environmentally friendly (low-impact) strategy for reducing Ni bioavailability and mitigating risks to agricultural systems and food crops.