A Potential Peanut Shell Feedstock Pyrolyzed Biochar and Iron-Modified Peanut Shell Biochars for Heavy Metal Fixation in Acid Mine Drainage

The biomass from peanut shells was pyrolyzed at 600 °C, and the resulting biochar was used as an adsorbent to extract heavy metals from acid mine drainage in the beginning. Initial screening findings showed that the peanut shell biochar had good affinity for Cu(II), Mn(II), Pb(II), and Zn(II), but not As(V). The adsorption process was predicted to achieve saturation in 200 min, and Pb had the maximum absorption at about 127 mg/g(II). Additionally, according to the Langmuir isotherm model, the order of the q_max(mg/g) was Pb(II) > Cu(II) > Zn(II) > Mn(II). The iron present in the acid mine drainage was recovered by precipitation and applied as sludge to change it in order to improve its affinity toward arsenic because the peanut shell biochar was unable to adsorb and remove arsenic. As a result, the alteration significantly increased the As(V) absorption, which uptake at about 8 mg/g. A thermodynamically stable interface may have formed as a result of the single layer of peanut shell biochar being stabilized on the surface of -Fe₂O₃(0001) by C-Fe chemical bonds through the terminal C atoms with an adhesion energy of only -0.315 eV Å^-2, according to theoretical insight from first principles DFT calculations. Pb was anticipated to have the strongest adsorption ((E_ad= -1.94 eV) and Zn to have the poorest adsorption (E_ad= 0.98 eV). Pb > Cu > Fe > As > Mn > Zn is the predicted trend for the adsorption in decreasing strength, which is consistent with the experimental findings and supports their potential for more acid mine drainage cleanup.