Objective: Magnetic biochar can be applied for heavy metal adsorption due to its low cost, high efficiency, large surface area, good thermal stability, and environmental friendliness. Due to porous structures and a larger specific surface area, magnetic biochar can serve as a very effective adsorbant during soil washing. The siderite magnetic biochar absorbent predominantly consists of magnetite, a ferrimagnetic substance characterized by notable magnetic properties. Thus, this absorbent suspension will get separated by using a simple magnet. The magnetic biochar composites serving as the adsorbent during soil washing were pyrolysed of siderite and sawdust under N₂ conditions. The characterizations indicated that magnetic biochar has been synthesysied.
Method: By pyrolysing siderite and sawdust together, magnetic biochar absorbent was synthesised. Soil samples with high contamination of considered heavy metals from previous research and area monitoring and sampling were prepared for soil-washing tests. The co-washing process of contaminated soil samples with magnetic biochar composites and weak acid elution was set up. The heavy metal adsorption on magnetic biochar during soil-washing remediation was conducted in a range of pH (2-8) and temperature (15-45 °C). After shaking for 10 hours and giving the rest time, solid-liquid phases were easily separated from the supernatant using a magnet. The analysis of heavy metal concentrations was conducted at the Geological Survey of Iran using inductively coupled plasma (ICP) methodology.
Results: The characterization results demonstrated that magnetic biochar possessed porous structures and exhibited an increased specific surface area. The siderite magnetic biochar absorbent was determined to be primarily comprised of magnetite, a ferrimagnetic material recognized for its substantial magnetic properties. At a pH of 5 and a temperature of 45°C, maximum adsorption of the magnetic biochar was gained, which was 154.45 for Pb, 272.08 for Cr, 378.35 for As and 3.29 for Cd. The rapid adsorption process could likely be attributed to the active sites present on the biochar. Furthermore, it was concluded that the primary mechanism governing the adsorption of heavy metals onto magnetic biochar was chemisorption and surface complexation.
Conclusions: According to the results, the pyrolysis of magnetic biochar was proven to be a cost-effective, highly efficient, and environmentally sustainable approach for soil remediation. The co-washing technique applied to contaminated soil samples significantly decreased the bioavailability of cadmium (Cd), lead (Pb), arsenic (As), and chromium (Cr) without markedly altering the soil's chemical properties. Consequently, this washing method incurs minimal ecological risks. Owing to its straightforward synthesis process, affordability, enhanced adsorption capacity, ease of separation, and overall environmental compatibility, magnetic biochar emerges as an effective adsorbent for soil remediation.