Background and aims <p>Contamination of agricultural soils with&#xa0;trace elements negatively affects plant growth, nutrient balance, and soil biological functioning. This study aimed to investigate the effects of different doses of zeolite–leonardite/lignite composites synthesized from fly ash on heavy metal bioavailability and uptake by plants in contaminated soil.</p> Methods <p>A two-year pot experiment with maize (<i>Zea mays</i> L.) was conducted. Changes in soil chemical properties, metal fractionation, and metal bioaccumulation, bioconcentration, and translocation were evaluated.</p> Results <p>Application of the composites significantly increased soil pH and cation exchange capacity while reducing the bioavailable fractions of Cd, Pb, and Zn. Sequential extraction (BCR) and risk assessment indices (Risk Assessment Code – RAC; Potential Ecological Risk Index – PERI) confirmed a marked reduction in ecological risk. Maize plants exhibited lower bioconcentration (BCF) and transfer (TF) factors, indicating limited translocation of metals from roots to shoots. The amendments also supported improved plant biomass without signs of metal stress. The use of mineral–organic mixtures affected the bioavailability and mobility of trace elements, with phytostabilization mechanisms dominating over phytoextraction.</p> Conclusions <p>The fly ash–derived mineral–organic composites effectively immobilized&#xa0;trace elements and enhanced soil buffering capacity, suggesting their potential as sustainable amendments for restoring productivity and ecological function in contaminated agricultural soils.</p>