Synthesis and characterization of a clay-coal waste-based adsorbent for contaminant removal from acid mine drainage

This study aims to develop an adsorbent material from solid coal waste and expanded clay to remove contaminants from acid mine drainage (AMD). A solid residue from coal extraction in the southern region of Santa Catarina, Brazil, and a clay from the same region were selected for the adsorbent synthesis. The synthesis process followed a full 3² factorial experimental design, varying composition (pure coal waste, mixture and, pure clay), particle size (fine (88 μm ≤ D ≤ 250 μm), medium (250 μm ≤ D < 840 μm), and coarse (840 ωm ≤ D < 2.380 μm), and mass, resulting in 36 tests. The results demonstrated that the developed adsorbents exhibited significant adsorption capacity for iron ions, with nearly 100 % removal of this contaminant using small quantities of adsorbent. For nickel ions, the best results showed approximately a 40 % reduction in the concentration of this heavy metal. Zinc ion concentrations were reduced by about 77 %. In all cases, the adsorbents developed in this study outperformed commercial activated carbon in adsorption capacity. Furthermore, the particle size of the adsorbents had a notable impact on adsorption performance, with smaller particle sizes leading to increased adsorption capacity, which can be attributed to the larger surface area.