Sorption of heavy metal ions onto crayfish shell biochar: Effect of pyrolysis temperature, pH and ionic strength

Abstract

Abstract In this study, crayfish shell was pyrolyzed at 300 (CS300), 450 (CS450) and 600 °C (CS600) to identify the optimum temperature for improving the binding capacity of the produced biochar. The removal efficiency of biochars was assessed following mono-element sorption of Pb(II) under batch sorption and fixed-bed column experiments. The effect of pH and ionic strength on Pb(II) sorption was further investigated on the most efficient biochar type to understand environmental factors affecting sorption onto crayfish biochar. Besides, this most efficient biochar was further investigated in multi-element sorption (Pb(II), Cu(II) and As(III)) trial to assess the effect of competitive sorption on Pb(II) bioavailability. Pyrolysis temperature had different effects on elemental composition, surface area and active functional groups of the produced biochar. CS600 showed the highest sorption capacity (190.7 mg/g) of Pb(II). Sorption mechanisms were identified following FTIR, SEM, XRD and ICP analyses suggested the participation of physisorption. Sorption of Pb(II) onto crayfish biochar was strongly pH- and ionic strength-dependent as the sorption capacity showed significant reductions at low pH and high ionic strength values. The competitive sorption of Pb(II) with other metal ions (Cu(II) and As(III)) showed its superiority to bind with active sorption sites of biochar as compared with other heavy metals.