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The adsorption mechanism of N-butoxypropyl-S-[2-(hydroxyimino) propyl] dithiocarbamate ester to copper minerals flotation

Jingjing Xiao, Guangyi Liu(, Hong Zhong

(School of Chemistry and Chemical Engineering, Central South Univeristy, Changsha, Hunan, China, 410083)

3.6. Adsorption kinetics and thermodynamics

3.6.1 Adsorption kinetics

The kinetics of BOPHPDT adsorption on to chalcopyrite surfaces were evaluated by using the pseudo-first-order (Lagergren 1898) and pseudo-second-order (Babu and Gupta 2008) models, and the pseudo-first order model is expressed as Equation (S1),

[pic] (S1)

Where, Qe is the adsorption capacity of chalcopyrite to BOPHPDT at equilibrium time, and k1 (h-1) is the rate constant of first-order adsorption.

The pseudo-second-order model (Babu and Gupta 2008) is given as Equation (S2),

[pic] (S2)

Where, k2 (m2·mol-1·h-1) is the rate constant of pseudo-second-order adsorption. The adsorption rate constants k1 and k2 for BOPHPDT sorption were calculated from the slope of the linear plot of ln(Qe-Qt) vs. time t and the intercept of the linear plot of t/Qt vs. t, respectively.

The adsorption data listed in Fig. 6 were fitted by using the pseudo first and second order kinetic models. The fitted curves and obtained kinetic parameters were shown in Fig. S1 and Table S1. The results in Table S1 showed that the correlation coefficient R2 values of the pseudo second order model (>0.99) were higher than those of the pseudo first order model (0.81-0.91). Moreover, the theoretical Qe values fitted by the pseudo second order kinetic model were closer to the experimental values. Therefore, the pseudo-second-order kinetic model was a preferable model for describing BOPHPDT adsorption on to chalcopyrite.

|[pic] |[pic] |

|Fig. S1. Pseudo- first-order (a) and pseudo-second-order (b) kinetic models of BOPHPDT adsorption onto chalcopyrite surfaces |

Table S1. Kinetic parameters of BOPHPDT adsorption on chalcopyrite surfaces

|T(K) |Pseudo first order |Pesudo second order |Qe-exp (mol·m-2) |

| |K1 (h-1) |R2 |Qe (mol·m-2) |K2 (m2·mol-1·h-1) |R2 |Qe (mol·m-2) | |

|298 |0.532 |0.813 |6.946×10-5 |11358.95 |0.997 |4.708×10-5 |4.161×10-5 |

|303 |0.334 |0.953 |3.445×10-5 |17587.90 |0.998 |4.857×10-5 |4.469×10-5 |

|308 |0.426 |0.914 |2.586×10-5 |30020.64 |0.999 |4.902×10-5 |4.658×10-5 |

The activation energy Ea (kJ·mol-1) of BOPHPDT adsorption on to chalcopyrite is calculated by using the Arrhenius Equation (S3) (Salah 2015).

[pic] (S3)

Where A is the Arrhenius pre-exponential factor, R is the universal gas constant and T is the temperature in Kelvin.

The values of lnk2 versus T-1 were plotted and shown in Fig. S2, displaying a good linear relationship with correlation coefficient R2=0.982. The slope and intercept were determined to be -8914.56 and 39.23, respectively. The activation energy Ea was calculated to be 74.12 kJ·mol-1, suggesting that BOPHPDT adsorption on chalcopyrite surfaces was a chemisorption process (Langmuir 1916).

[pic]

Fig. S2. Relationship between lnK2 and T-1

3.6.2 Adsorption thermodynamics

The equilibrium data of BOPHPDT adsorption on chalcopyrite as listed in Fig. 7 were fitted by the Langmuir and Freundlich isotherm models. The Langmuir equation is given as Equation (S4) (Langmuir 1918).

[pic] (S4)

Where Qm is the maximum monolayer adsorption capacity of chalcopyrite for BOPHPDT (mol·m-2), and KL is the binding constant (L·mol-1).

The linear form of Freundlich isotherm model (Freundlich 1906) can be written as Equation (S5):

[pic] (S5)

Where, KF represents the adsorption capacity when equilibrium concentration equals unity, and means the average affinity of a solute toward a solid surface. n is an indicator of surface heterogeneity and adsorption favorability (Frimmel and Huber 1996). The values of KF and n are obtained from the intercept and slope of linear fitting line of the lnQe vs. lnCe plot.

The equilibrium data of BOPHPDT adsorption on chalcopyrite were fitted by Langmuir and Freundlich isothermal equations and the fitted curves were shown in Fig. S3. The obtained isothermal parameters were given in Table S2. Fig. S3 and Table S2 demonstrated that the correlation coefficient R2 values for Langmuir or Freundlich model were over 0.98, implying the adsorption might be a monolayer adsorption on heterogeneous surfaces, which was similar to the findings of Gupta et al. (2010). While, the R2 values fitted by Langmuir models were slightly larger than those by Freundlich models. Thus, the Langmuir adsorption constants were chose to fit the adsorption thermodynamic parameters. Table S2 also showed Qmax values were relatively large, implication to the strong affinity of chalcopyrite to BOPHPDT, and the KL values were all greater than zero, suggestion on a favorable adsorption of BOPHPDT on chalcopyrite surfaces.

|[pic] |[pic] |

|Fig. S3. Langmuir (a) and Freundlich (b) models of BOPHPDT adsorption onto chalcopyrite |

Table S2. Isotherm parameters for BOPHPDT adsorption on to chalcopyrite

|T/K |Langmuir |Freundlich |

| |KL (L·mol-1) |Qmax (mol·m-2) |R2 |KF (mol·m-2) |n |R2 |

|298 |1.791×104 |1.034×10-4 |0.992 |0.072 |1.288 |0.987 |

|303 |2.410×104 |1.248×10-4 |0.999 |0.043 |1.239 |0.991 |

|308 |2.881×104 |1.280×10-4 |0.994 |0.035 |1.273 |0.984 |

According to the Van’t Hoff equation, the relationship between the adsorption coefficient KL from the Langmuir adsorption isotherm and temperature is expressed as Equation (S6) (Gupta et al. 2008).

[pic] (S6)

Here ΔΗ is enthalpy change (J·mol-1), ΔS is entropy change (J·mol-1·K-1), R is the universal gas constant (8.314 J·mol-1·K-1), and T is the absolute temperature (K).

The Gibbs free energy change ΔG is calculated from Equation (S7).

[pic] (S7)

The values of lnKL versus T-1 were plotted and displayed in Fig. S4, exhibiting a good linear relationship (the correlation coefficient R2=0.930) with the slope and intercept values determined to be -4370.67 and 24.48, respectively. The adsorption enthalpy change ΔH and entropy change ΔS were calculated and reported in Table 3 along with the Gibbs free energy change ΔG calculated from Equation (S7).

[pic]

Fig. S4. Relationship between lnKL and T-1

3.8. Zeta-potential measurements

[pic]

Fig. S5. High-resolution Cu 2p3/2 XPS spectra of chalcopyrite

References

Babu, B. V., Gupta, S., 2008. Adsorption of Cr (VI) using activated neem leaves: kinetic studies. Adsorption 14, 85-92.

Freundlich, H., 1906. Adsorption in solution. Phys. Chem. Soc. 40, 1361-1368.

Frimmel, F. H., Huber, L., 1996. Influence of humic substances on the aquatic adsorption of heavy metals on defined mineral phases. Environ. Int. 22, 507-517.

Gupta, V. K., Mittal, A., Gajbe, V., Mittal, J., 2008. Adsorption of basic fuchsin using waste materials-bottom ash and deoiled soya-as adsorbents. J. Colloid Interface Sci. 319, 30-39.

Gupta, V. K., Rastogi, A., Nayak, A., 2010. Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry wastematerial. J. Colloid Interface Sci. 342, 135-141.

Lagergren, S., 1898. Zurtheorie der sogenannten adsorption gelosterStoffe. K. Sven. Vetenskapsakad. Handl. 24, 1-39.

Langmuir, I., 1918. The adsorption of gases on plane surfaces of glass, mica and platinum. J. Am. Chem. Soc. 40, 1361-1368.

Langmuir, I., 1916. The constitution and fundamental properties of solids and liquids. Part I. solids. J. Am. Chem.Soc. 38, 2221-2295.

Salah, A. M. I., 2015. Adsorption, kinetic and thermodynamic studies for manganese extraction from aqueous medium using mesoporous silica. J. Colloid Interface Sci. 440, 84-90.

( Corresponding author. Tel.: +86 731 88830654; fax: +86 731 88879616.

E-mail address: lgy_2013@csu. (Guangyi Liu)

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