Ammonium citrate-modified biochar: An adsorbent for La(III) ions from aqueous solution

Abstract

Biochars were fabricated from marine biomass Sargassum fusiforme through slow pyrolysis under vacuum at 300, 500, or 700°C and modified using ammonium citrate (AC) as a high-efficiency absorbent for trivalent lanthanum, La(III). Fourier transform infrared spectroscopy (FT-IR) analysis indicated that the amino and carboxyl groups were bound to the biochar surface. The adsorption abilities of the pristine and AC-modified biochars derived from S. fusiforme for La(III) were investigated in terms of the effects of initial pH, contact time, initial metal ion concentration, and interfering ions. The results demonstrated that the carboxyl-amino-modified biochar exhibited excellent adsorption performance for La(III). The adsorption capacity of the AC-modified biochar was 2.1-fold of the capacity of pristine biochar prepared at the same temperature. The Langmuir isotherm model fitted the experimental data quite well, with Langmuir monolayer adsorption capacities for the biochars pyrolyzed at 300, 500, 700°C, and AC-modified biochar pyrolyzed at 300°C (AC-BC300) were 170.36, 185.53, 275.48, and 362.32mgg−1, respectively. Data obtained from kinetics studies indicated that the adsorption of La(III) onto the biochars obeyed a pseudo second-order kinetic model. In addition, the AC-BC300 after adsorption could be effectively regenerated by HCl solution. As La is a typical member of the lanthanide series, our results suggest that the biochars derived from S. fusiforme could also function as potential low-cost adsorbents for the removal of rare earth pollutants from aqueous waste streams.