Superior Removal of Toxic Cr(VI) from Wastewaters by Natural Pine Bark

Hexavalent chromium (Cr(VI)) is one of the most toxic heavy metals found in industrial wastewater, so many researchers are working to develop efficient and environmentally friendly removal methods. It has been reported that natural biomass and its derivatives can be used to treat wastewaters containing Cr(VI). However, biomass with sufficient Cr(VI) removal performance to replace the existing chemical method, which is cheap and simple, has not been reported yet. This study reports that inexpensive, abundant, and commercially available pine bark has the highest Cr(VI) removal capacity (i.e., 376.3 mg/g) compared to biomass reported elsewhere. This value is six times higher than the theoretical value of an inorganic reducing agent (iron(II) sulfate heptahydrate). The main mechanism of Cr(VI) removal by pine bark was clearly identified through kinetic experiments, Fourier-transform infrared spectrometer, and X-ray photoelectron spectroscopy analyses, which were used to study the compositions, functional groups, and bonding states of pine bark. It was found that pine bark consists of various acidic functional groups that can act as electron donors to promote the removal of Cr(VI) through redox reactions. In conclusion, pine bark may be a promising candidate for the removal of Cr(VI) from wastewater, owing to its excellent removal capacity.