Pyrolytic behavior of a zero-valent iron biochar composite and its Cu(ii) removal mechanism.

The reduction behavior of Fe 3+ during the preparation of a zero-valent iron cocoanut biochar (ZBC8-3) by the carbothermic reduction method was analyzed. Fe 3+ was first converted into Fe 3 O 4 , which was subsequently decomposed into FeO, and finally reduced to Fe 0 . A minor amount of γ-Fe 2 O 3 was produced in the process. The isothermal thermodynamic data for the removal of Cu(ii) over ZBC8-3 followed a Langmuir model. The Langmuir equation revealed a maximum removal capacity of 169.49 mg g -1 at pH = 5 for ZBC8-3. The removal of Cu(ii) over ZBC8-3 fitted well to a pseudo-first-order equation, which suggested that the rate limiting step of the process was diffusion. The Cu(ii) removal mechanism on ZBC8-3 involved the reduction of Cu(ii) by Fe 0 to produce Cu 0 and Cu 2 O, while C[double bond, length as m-dash]C, C-O-, and -O-H formed a complex with Cu(ii).