| Biosorption experiments were performed using Mycobacterium phlei as adsorbent for Cd2+ and Cr6+. The biosorption characteristics, effects of several factors on biosorption and desorption were investigated in this experiment. And mechanisms of the adsorption on live pellets were revealed on the basis of dynamics and thermodynamics.Combined with single factor experiment and orthogonal design, the subject carefully studied the influence of pH, temperature, biomass, ion concentration, adsorption time towards the adsorption of Cd2+ and Cr6+ by Mycobacterium phlei. Optimum condition for adsorption was also examined in the study. The results showed that the adsorption rate of Cd2+ reached 92.48% in condition of pH value was 5.00, concentration of Cd2+ was 30mg·L-1, adsorbent mass was 10g·L-1, adsorption time was 40min, temperature was 35℃. The adsorption rate of Cr6+ reached 94.67% in condition of pH value was 2.00, concentration of Cr6+ was 40mg·L-1, adsorbent mass was 8g·L-1, adsorption time was 90min, temperature was 40℃. The adsorption capacity was found to increase as the adsorbent mass increase, but decrease as the ion concentration increase. The adsorption process is quick and adsorption equilibrium is attainable within 30 minutes.The Mycobacterium phlei was domesticated on the basis of its tolerances to Cd2+ and Cr6+, respectively. Then studied the influence of temperature, pH, adsorption time, biomass, ion concentration towards the adsorption of Cd2+ and Cr6+ by domesticated Mycobacterium phlei combined with single factor experiment and orthogonal design. The orthogonal design results showed that when pH value was 5.00, concentration of Cd2+ was 60mg·L-1, adsorbent mass was 28g·L-1, adsorption time was 90min, temperature was 35℃, the adsorption rate reached the maximum of 94.27% and when pH value was 2.00, concentration of Cr6+ was 70mg·L-1, adsorbent mass was 32g·L-1, adsorption time was 90min, temperature was 35℃, the adsorption rate reached the maximum of 95.79%. As to the domesticated Mycobacterium phlei, its adsorption rate of Cd2+ and Cr6+ increased by 20.46% and 16.85% respectively compared with that of the Non-domesticated Mycobacterium phlei under the same conditions.The Mycobacterium phlei pretreated with different methods have different effects on biosorption that pretreated with acid and alkali can enhance the adsorption rate of Cd2+ and Cr6+ respectively. The desorption experiment using five kinds of agents suggested that NaOH and HCl were suitable for the desorption of Cr6+ and Cd2+, respectively.It was shown by zeta potential of Mycobacterium phlei and existing state of heavy metal ions that the isoelectric point of Mycobacterium phlei was 3.10, which indicated that electrostatic adsorption plays an important role on the biosorption of Cd2+ and Cr6+.The adsorption of both Mycobacterium phlei and domesticated strains on Cd2+ and Cr6+ accorded with Langmuir and Freundlich adsorption isotherm. The line obtained by Langmuir adsorption isotherm had better relativity, which indicated that the adsorption by these strains was a complex process including not only physical adsorption but also chemical adsorption. The dynamic adsorption processes follow a pseudo second-order kinetic rate equation very well. |
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