Carbon nanofibers: A new adsorbent for Au (III)

Introduction: The presence of metal in industrial effluent is one of the most crucial preoccupations nowadays due to the adverse environmental effect. Some of this metal could be considered valuables. So the effluent... [ view full abstract ]

Introduction:

The presence of metal in industrial effluent is one of the most crucial preoccupations nowadays due to the adverse environmental effect. Some of this metal could be considered valuables. So the effluent treatment before final discharge to recover and/or eliminate the metals is necessary [1].

Adsorption is a high efficiency, cost–effectiveness and easily handing method to recover metals from effluent liquids [2]. Currently are emerging new adsorbent nanomaterials. Among nanomaterials carbon nanofibers (CNF) show a great potential to be efficient adsorbents for the adsorption of all kinds of metal ions [3], especially heavy metals ions, such as gold, one of the most precious metals in the world.

The aim was to establish the adequate conditions for achieving gold adsorption by carbon nanofibers.

Methods:

Batch adsorption and desorption experiments were carried out in a glass reactor provided or mechanical shaking. The gold was determined by AAS.

%Au_ad=[(C_o-C_e)/C_e]x100

C_e(mg Au L^-1) in solution.

Adsorption parameters investigated were stirring speed, temperature, HCl, CNF and Au(III) concentration.

Result and discussion:

Experimental result shows that it is possible to use CNF to recover Au(III) in effluent liquid at HCl medium. Figure 1 shows the effect of contact time on the gold adsorption, at 5 min over the 94% of total sorption has been occurred, and reach a maximum between 30-60 min, indicating that the sorption is a rapid process. The involved reaction could be:

a) Direct reduction

AuCl₄^- + 3 e^-      →         Au⁰ + 4 Cl^-                E⁰=1.00V                              (1)

b) Reduction via AuCl₂^-

AuCl₄^- + 2 e^-     →          AuCl₂^- + 2Cl^-             E⁰= 0.92V                             (2)

AuCl₂^- + e^-         →         Au⁰ + 2 Cl^-                E⁰= 1.00V                             (3)

CNF is the electron donor

C + 2H₂O         →          4 H⁺ + CO₂ + 4e^-        E⁰=0.21 V                             (4)

Figure 2 shows the gold particles.

Reference:

1.- D. de Agreda, I. García-Díaz, F.A. López, F.J Alguacil. (2011). Revista Metalurgia, 47(2), 146-168

2.- Y.C. Sharma, V. Srivastava, V.K. Singh, S.N. Kaul, C.H. Weng. (2009). Environmental Technology, 30 (6), 583-609

3.- X. Li, S. Chen, X. Fan, X. Quan, F. Tan, Y. Zhang, J. Gao. (2015). Journal of Colloid and Interface Science, 447,120-127