Adsorption Kinetics of Cadmium and Lead by Biochars in Single- and Bisolute Brackish Water Systems

Cd(II) and Pb(II) adsorption from brackish water by activated carbon (AC) and biochars derived from bamboo (BB), palm shell (PSB), and mangrove wood (MB) in single- and bisolute systems was investigated. Physicochemical characterization including SEM, FTIR, pH, pH , elemental analysis, proximate analysis, XRF, iodine number, BET surface area analysis, and TGA was carried out. The adsorption of Cd(II) and Pb(II) was in the following order: AC > BB > MB > PSB and was higher in single-solute than bisolute systems with greater Pb(II) adsorption efficiency than Cd(II). Salinity negatively affected metal sorption, particularly for Cd(II), but higher pH enhanced removal. Upon increasing the salinity from 0 to 25 ppt, the removal efficiency of BB was reduced from 75.9 to 52.2% (Cd) and 91.1 to 80.5% (Pb) in the single-solute system. In addition, the removal efficiency was decreased from 71.6 to 41.3% for Cd(II) and 90.9 to 76.3% for Pb)(II) in the bisolute system. The removal trend of the adsorption system of BB with 0 ppt salinity responded positively upon increasing pH from 5 to 8, and the removal of Cd(II) was increased from 54.4 to 75.8% and that of Pb(II) was increased from 66.3 to 91.0% in the single-solute system. The adsorption kinetic data are well explained by the pseudo-second-order model suggesting that chemisorption is the rate-limiting step. The key results of the present work suggest the applicability of BB as an alternative adsorbent to AC due to its comparable physicochemical properties, such as surface area (191.95 m /g), pore volume (0.1038 cm /g), pH (9.27), iodine number (104.2 mg/g), and the presence of hydroxyl (-OH), amine (-NH), and COO- groups necessary for metal bonding. The adsorption performance of BB is promising, and hence, it can be considered to remove the Cd(II) and Pb(II) ions from brackish water as statistically it is the least impacted by change in salinity at a confidence level of ≤ 0.05 compared to MB and PSB.