Preparation and modification of Prosopis juliflora biochar and Pb (II) removal from aqueous solutions

Lead (Pb (II)) is one of the hazardous heavy metals that cause significant harm to humans and it is primarily contaminated by water. Many physical and chemical adsorbents are used for removal of lead from wastewater but are not economical and ecofriendly. Biochar is a promising carbon material to adsorb Pb(II) by its large surface area and functional moiety diversity. In this research, the biochar was prepared from Prosopis juliflora and modified using phosphoric acid (H3PO4) and nitric acid (HNO3) for the removal of Pb (II) from wastewater, with the dual goals of resource management and environmental remediation. To evaluate the efficiency and obtain insights into the major mechanisms implicated in the removal of Pb (II), the pristine and modified biochar was investigated using XRD, FTIR, Raman spectroscopy, FE-SEM, TGA, and elemental analysis. A batch experiment was conducted by using Pb contaminated spiked with water. The influence of multiple control factors such as adsorbent dosage (0.5-4 g L-1), contact time (1-6 h), initial Pb concentration (10-50 mg L-1), and solution pH (2-8) on the removal of Pb (II) was studied. The pristine, phosphoric, and nitric acid-modified biochars had the highest adsorption capacities of 10.98, 17.32, and 18.72 mg g(-1), respectively. In comparison to the Langmuir model, the Freundlich adsorption isotherm perfectly fits the experimental results. However, the pseudo-second- order kinetic model was well described rather than pseudo-first-order and intraparticle diffusion model kinetic data. The adsorption effects of biochar on Pb(II) were in the order of HNO3 >H3PO4 > pristine biochar. Based on the experimental results, it was concluded that the acid modification of biochar was found to be effective for improving the adsorption capacity of Pb (II). Further, it overcomes the issue of biomass disposals by biochar production and helps to maintain the sustainable green environment.