Study On The Synthesis Of Activated Carbon Fiber Modified By Microwave In Acid Condition And Its Application For Pb(?) Adsorption

In this paper, activated carbon fiber was modified by microwave irradiation in acid condition, and the modification conditions, influencing factors on adsorption, adsorption kinetics, thermodynamics and adsorption mechanism were studied further, the main research contents are as follows:(1) The effects on Pb(?) adsorption properties affected by the modification condition of activated carbon fiber were investigated, and the optimal modification conditions were determined. The research results showed that, the Pb(?) adsorption effects on the activated carbon fiber which was prepared under the modification condition that volume ratio of HNO3/H2SO4 was 1:3, microwave power was 400 W, microwave time was 5min, microwave temperature was 75?, was the best, which was marked as M-ACF. Comparing with the ACF, the Pb(?) adsorption capacity and removal rate on the M-ACF improved significantly under the same condition. Meanwhile using SEM, XRD, FTIR, EDAX, isoelectric point, Boehm method to characterize ACF and M-ACF, in which the isoelectric point, Boehm, FTIR, EDAX and M-ACF characterization results showed that the activated carbon fiber modified by microwave in acid condition, the surface of which negatively charged carboxyl groups, ester and alcohol hydroxyl and other acidic oxygen functional groups increased significantly, was conducive to the adsorption of Pb(?); through analysing the results of specific surface area, the effects of strong oxidation in mixed acid and microwave irradiation led to the collapse of the activated carbon fiber pore wall, which causing M-ACF's specific surface area was significantly less than ACF's; SEM results indicated that after modification, the length and the surface of the activated carbon fiber became shorter and rougher, respectively; XRD results showed that the crystallinity of two fibers was poor, after modification, the graphite block structure was not changed.(2) The effects of solution pH values, adsorption time, adsorbent dosage, initial Pb(?) concentration, coexisting ions on Pb(?) adsorption properties were investigated. The solution pH values influenced the Pb(?) adsorption effects of two fibers; when the Pb(?) solution pH was 6, Pb(?) adsorption effects of two fibers were the best. Considering the cost and effect of adsorption, the best adsorbent dosage was 0.2g/L. Pb(?) adsorption on ACF and M-ACF could reach equilibrium after 80 min, 180 min, respectively. The influence sequence of Pb(?) removal rate for four co-existing ions in order were: Ca2+ > Mg2+ > K+ > Na+, and with the increasing co-existing ion concentration, Pb(?) removal rate on fibers was reducing continually.(3)Two kinds of fibers adopted 0.1mol/L dilute nitric acid solution which can obtain better regeneration effect, the Pb(?)desorption rate after regeneration were up to 97.5%, 92.1%, respectively; Pb(?) removal rate could reach 90.9%, 34.7%,respectively. M-ACF's Pb(?) removal rate after five times regeneration remained above 80%, while ACF's Pb(?) removal rate after regeneration was higher after more regeneration.(4) In the paper, the removal of Pb(?) kinetics, thermodynamic characteristics and adsorption mechanism on ACF and M-ACF were studied. Pb(?) adsorption on ACF, M-ACF followed the pseudo-second-order kinetic model and Langmuir isotherm model, respectively. The calculated Gibbs energy change ?G< 0, enthalpy change ?H> 0; and with the the reaction temperature rising, the absolute value of ?G became larger, indicating that the reaction was a spontaneous endothermic reaction; entropy change ?S>0 indicated that the process of reaction was entropy increase reaction. The mechanism conclusion was: the physical adsorption was primary for the adsorption on ACF while the chemical adsorption was primary for the adsorption on M-ACF.The results of this paper showed that the capacity of modified activated carbon fiber for Pb(?) adsorption had been significantly improved. Not only the activated carbon fiber modified by microwave in acid mixtures has good adsorption properties of Pb(?), but also it provides a new way for treating the lead-containing wastewater which has broad application prospects.