| With the rapid development of modern industry, a large amount of wastewater containing heavy metals was produced, this caused serious pollution to the environment and human health. How to eliminate the harm of heavy metals and reuse these precious metals effectively were outstanding problems faced to the current environmental protection work. Biosorption can be a promising alternative method to treat industrial effluents, mainly because of its low cost, high metal binding capacity, high efficiency in dilute effluents and environmental friendly.In this paper, some biosorbents were prepared using antibiotic fermentation dregs from pharmaceutical enterprises by chemical modification and adsorption properties of Pb(Ⅱ) and Cd(Ⅱ) on these biosorbents were studied. By using batch adsorption techniques, the influence of pH, adsorbent dosage, concentration, time and temperature on adsorption effect were investigated. In addition, the adsorption thermodynamics and the adsorption kinetics were studied systematically.The results showed that:(1) With pH increasing, the adsorption of raw antibiotic fermentation dregs to Pb(II) and Cd(II) increased gradually. It found that the optimum pH was 3 for Pb(II) and 5 for Cd(II), respectively. In addition, with the dosages increasing, the removal of Pb(II) and Cd(II) also increased gradually. When the dosages reached to 20 g/L, the removal of Pb(II) remained 97.36%, and adsorption rate of Cd(II) was 65.90% then stayed stable, Furthermore, with the initial concentration of metal ion increasing, adsorption quantity increased gradually, on the contrary, the adsorption rate showed a downward trend. The maximum adsorption rates of Pb(II) and Cd(II) were 97.22% and 65.24%, respectively, and maximum adsorption capacity was 14.39 mg/g and 7.82 mg/g, when solution concentration was 25 mg/L.(2)As temperature increasing, the adsorption rate of Pb(II) gradually increased, while Cd(II) reduced. The experimental adsorption data for antibiotic fermentation dregs adsorption to Pb(II) was fitted to Freundlich isotherm model while adsorption to Cd(II) was fitted to Langmuir model.(3)The adsorption rate of raw antibiotic fermentation dregs to Pb(II) reached to 91.45% in 60 min, and the adsorption of Cd(II) was fast during the first 50 minutes, the adsorption rate was 65.70%. The adsorption of two metal ions had reached equilibrium within 210 minute and adsorption kinetics were fitted to pseudo-second order equation.(4)The optimum pH of Citric acid modified dregs adsorption process to Pb(II) and Cd(II) was same to raw antibiotic fermentation dregs adsorption process, were 3 and 5, respectively. When the dosages of acid trested antibiotic fermentation dregs reached to 20 g/L, the removal of Pb(II) remained 98.25%, and adsorption rate of Cd(II) was 93.01% then stay stable. The maximum adsorption rates of Pb(II) and Cd(II) were 99.63% and 92.9%, respectively, and maximum adsorption capacity was 20.84 mg/g and 12.96 mg/g, when solution concentration was 25 mg/L.(5) With the temperature rising, the adsorption rate of Pb(II) by Citric acid modified dregs increased, while that of to Cd(II) decreased. Pb(II) adsorption by Citric acid modified dregs was fitted to f, while l fitted Cd(II) adsorption.(6) In the adsorption process of Pb(II) and Cd(II) by Citric acid modified dregs, the adsorption rate to Pb(II) were 95.35% at 30 min, and the adsorption of Cd(II) was fast during the first 60 minutes, the adsorption rate was 91.04%. The adsorption of two metal ions have reached equilibrium within 180 min and adsorption kinetics were fitted to pseudo-second order equation.(7) In the adsorption process of Pb(II) and Cd(II) by Citric acid modified and raw antibiotic fermentation dregs, the free energy change( G) were negative, which indicated the adsorption process was spontaneous. The enthalpy change( H) and entropy change( S) of Pb(II) were positive, which demonstrated that the adsorption process were of endothermic process and chaotic degree of solid/liquid junction were increased. While The enthalpy change( H) and entropy change( S) of Cd(II) were all negative, which showed that the adsorption process were of exothermic process and chaotic degree of solid/liquid junction were reduced. |
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