The adsorption behavior of Au(Ⅲ) onto Aspergillus niger biomass was investigated in aqueous solutions.The effects of pH value

contact time

temperature and initial Au(Ⅲ) concentration on the adsorption were studied.The results indicated that Au(Ⅲ) adsorption onto Aspergillus niger was slightly pH-dependent and the pH value of 2.0—3.0 was favorable.The process was obviously accelerated with the increase of temperature in the range of 20—60℃.Au(Ⅲ) adsorption involved two stages at 20℃

corresponding to the periods before and after Au(Ⅲ) reduction and achieved equilibrium at a contact time of 24 h

while the adsorption proceeded in one stage at 30

40 and 60℃ and achieved equilibrium at 12

6

and 1 h

respectively.The adsorption capacity was hardly affected by temperature at lower initial Au(Ⅲ) concentrations(<233.32 mg·L-1)

while a significant increase was observed with the increase of temperature at higher Au(Ⅲ) concentrations(>367.94 mg·L-1).Au(Ⅲ) adsorption fits the Langmuir model well

and the maximum Au(Ⅲ) uptake capacity is 185.19

202.02

235.85 and 277.78 mg·g-1 at 20

30

40 and 50℃

respectively.The calculated thermodynamic parameters such as Gibbs free energy

enthalpy and entropy changes(ΔG0

ΔH0

ΔS0) reveal that this biosorption is spontaneous and endothermic and entropy increases.The adsorption process conforms to the pseudo-second-order kinetics

with the activation energy of 55.71 kJ·mol-1.Fourier transform infrared spectra illustrate that the functional groups such as amido

carboxyl and hydroxyl may be responsible for the interaction between Au(Ⅲ) and Aspergillus niger biomass.