Assessing the Efficiency of Chemically Modified Biochars in Removing Nickel From Aqueous Solutions

Background: Modification methods can significantly alter the adsorption properties of biochar by changing its structure. This study aimed to optimize the removal of Ni2+from aqueous solutions using unmodified pristine biochar (PB) and acid-modified biochar (ACB) and alkali-modified biochar (ALB) treatments. Methods: After producing unmodified and modified biochars, their efficacy (PB, ACB, ALB) in optimizing nickel (Ni) removal from aqueous solutions, affected by various factors including initial Ni concentration, solution pH, adsorbent dose and contact time was evaluated using the response surface methodology (RSM: Box-Behnken design). Results: Comparative analysis employing Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed that ACB and ALB biochars exhibited an improved aromatic structure and smoother surfaces compared to PB. However, the modification process resulted in a decline in specific surface area (SSA) for ACB and ALB, consequently reducing their Ni adsorption capacity compared to PB. It was observed that acidic and alkaline treatments caused dissolution and rearrangement of biochar components, leading to a decrease in porosity and SSA. Consequently, the modified biochars demonstrated diminished effectiveness in removing Ni from solutions. Furthermore, the study revealed that pH, contact time, and adsorbent dose directly affected the Ni removal, while the initial Ni concentration exhibited an inverse effect. Conclusions: The current study revealed that the modification of biochar does not invariably enhance its pollutant adsorption properties. Further research is needed to explore the influence of feedstock types and the specific method of biochar modification on its pollutant adsorption efficiency.