Waste-art-paper biochar as an effective sorbent for recovery of aqueous Pb(II) into value-added PbO nanoparticles

In order to improve the recycling of waste paper and metallic ions in waste water, waste art paper with high contents of fillers/adhesives was carbonized at 300, 450, and 600 °C and the resulting engineered biochars were used to recycle the aqueous Pb(II). The waste-art-paper biochars obtained at higher temperature showed extraordinary removal of aqueous Pb(II) with the Langmuir maximum sorption capacity of 1555 mg g⁻¹, significantly higher than that of other carbon sorbents in literatures. Comparison of Pb(II) sorption onto biochar's deashing component and ash suggested the important role of minerals in Pb(II) sorption. The pH changes and the releases of Ca²⁺ after Pb(II) sorption further suggested the reactions between calcite minerals of the biochars with the lead ion during Pb(II) sorption. Characterizations of pristine and post-sorption biochars with scanning electron microscope equipped with an energy dispersive spectrometer, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron analyses confirmed the precipitation of Pb(II) with CO₃²⁻ to form PbCO₃ and Pb₂(OH)₂CO₃ crystals on the biochar surfaces. As a result, acid extraction (1.0 mol L⁻¹ HNO₃) effectively recycled all the sorbed lead. Furthermore, incineration of Pb(II)-laden biochar under 350 °C not only successfully recovered the lead but also turned it into high purity (>96%) PbO nanoparticles. Findings from this work indicated that recycle waste art paper for biochar production can be a promising environmentally friendly and cost-effective technology because of the extraordinary sorption ability of waste-art-paper biochar and the effective recovery of sorbed Pb(II) into value-added nanoparticles from exhausted biochar.