This study investigates the synthesis and performance of a biochar-based composite, integrating montmorillonite (MMT) and ZnAl layered double hydroxide (LDH), for the removal of Fe and Mn from acid mine drainage. The biochar_MMT_ZnAl LDH composite, synthesized from solid waste materials, was characterized using BET, XRD, FTIR, TGA, and SEM-EDS analyses. The material demonstrated a surface area of 117.54 m²/g and a pore volume of 0.21 cm³/g, significantly surpassing non-composite biochar with a surface area of 14.81 m²/g. The batch sorption experiment showed rapid adsorption kinetics, achieving 99% Mn removal within 7 min at 0.5 g adsorbent dosage, reducing Mn concentration from 100 mg/L to 0.07 mg/L. For Fe, an 87% reduction was achieved after 400 min using 0.5 g of plain biochar, while biochar_MMT_ZnAl LDH showed superior adsorption performance with a final Fe concentration below 0.07 mg/L. Adsorption isotherm analysis indicated that biochar followed the Dubinin–Radushkevich model, while the composites adhered to the Redlich–Peterson model. Kinetic studies revealed a strong fit with the Pseudo-Second-Order model (R² = 1 for biochar_MMT), suggesting chemisorption as the dominant mechanism. Thermodynamic analysis confirmed the spontaneity and endothermic nature of the adsorption process, with ΔG values ranging from − 18,758 to − 92,932 J/mol for Fe and Mn removal. The findings highlight the potential of biochar-based composites in developing cost-effective and environmentally sustainable solutions for acid mine drainage treatment.

The kinetics study has an essential role in the scale-up process because it illustrates the real phenomena of a process. This study aims to develop a mathematical model that can explain the mechanism of the leaching process of laterite ore using a low concentration of the citric acid solution and evaluate that model using the experimental data. As a raw material, this process used powder-shaped limonite laterite ores with a size of 125–150 µm. The leaching process is carried out using 0.1 M citric acid solution, F:S ratio of 1:20, and a leaching time of 2 h. The temperature parameter was varied at 303, 333, and 358 K. The experimental results showed that the higher the operating temperature, the higher the extracted nickel. The results of this experiment were used to evaluate the shrinking core kinetics model and the lumped model. The simulation results for both models show that the lumped model can provide better simulation results. Quantitatively, the percentage of errors from the shrinking core model is around 3.5 times greater than the percentage of errors from using the lumped model. This result shows that in this leaching process, the process mechanism that occurs involves the reactant diffusion step and the chemical reactions step; those steps run simultaneously.

Solid pollution has been an issue in mineral processing for decade. One of these pollutants is zircon sand mining waste (zircon tailing). Due to the concentration of rare earth minerals in zircon tailing and the increasing demand of REE in advanced technologies, studying zircon tailing as a potential source of REE had become an interest for us. Our experiments consisted of mineral characterization and an alkaline fusion process, followed by a leaching process. The characterization process was carried out to obtain actual information from zircon tailing samples. This process showed total rare earth elements (REEs) content of 58.62%, at 9%, 1%, 1.2%, 1.7%, and 1.5% for Y, Gd, Er, Dy, and Yb, respectively. A sieving process was carried out since it was known that most heavy rare earth elements (HREEs) content occurs at a larger size. The alkaline fusion process was applied with an intent to break the phosphate bonds present in the REE-carrying minerals (xenotime and monazite) and convert phosphate bonds to hydroxide bonds in rare earth metals. During the alkaline fusion process, as much as 75%, 66.45%, and 60% of the phosphate, silica, and zirconium, respectively, were reduced. The leaching process was carried out in a flat-bottom three-neck flask. The optimum point of leaching experiments occurs at 0.5 M H2SO4, 60°C, and a solid-to-liquid (S/L) ratio of 10 g/100 mL. In these conditions, as much as 89%, 99%, 94%, 92%, and 90% of Y, Gd, Er, Dy, and Yb, respectively, were recovered as an HREEs2-(SO4)3 product solution.