Mechanism on Cr(VI) removal from aqueous solution by camphor branch biochar

Removal of Cr(VI) from aqueous solution by biochar obtained from landscaping waste of camphor branch was investigated in order to find new material in producing carbon-based sorbent. Cr(VI) removal efficiency experiments revealed that the optimum pyrolysis temperature of camphor branch was 350 °C (CBB350) and an initial solution pH at 2.0 was favorable for Cr(VI) removal. The characteristics and mechanism of CBB350 on Cr(VI) removal were studied via Brunauer - Emmett - Teller nitrogen adsorption method, the scanning electron microscope equipped with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer and kinetic analysis. The results suggested that Elovich equation was best fitted the complex reaction process with fitting correlation coefficient above 0.94, which prompted that the chemical reaction was the control step, the concentration of Cr(VI) decreased sharply at the beginning of the reaction and the removal rate was accelerated in high temperature. The removal mechanism was supposed that the vast bulk of Cr(VI) was reduced to Cr (III) through electrostatic interaction or form new stable inorganic ions and hexa-coordinate complexes chemically adsorbed on the surface of camphor branch biochar, a fraction of Cr(VI) was reduced to Cr (III) species retained or discharged in the solution and the rest Cr(VI) was directly adsorbed on the adsorbent.