| As a species of platinum group metals(PGMs),Palladium is widely used in industry,automobile,aerospace,medical instruments and catalyst preparation.The distribution of palladium in the world is extremely deficient and inhomogeneous.What's more,the distribution of palladium in our country is less than 0.5% of the world.As precious metal resources are scarce,widely used and in great demond,the technology of recovering industrial waste water,mineral waste residue and production waste,has received extensive attention in recent years..In this study,-C=S modified chitosan fiber(SCF)was prepared using chitosan as the matrix,and epichlorohydrin(ECH)and GA as two-step crosslinking agent,respectively,to add the amino group and Sulfur atom to the chitosan.The resultant modified chitosan fibers were used to recovery Pd(II)from acidic solutions with a high Pd(II)adsorption capacity and good acid resistance.The results are showing as following in details:(1)ECH of first crosslinking,GA,TU,pH of modification and GA of second crosslinking were critical factors to Pd(II)adsorption capacity for the preparation process of the modified chitosan fiber.A five factors of five levels experiment were conducted to opmitize the condition of the preparation process of the modified chitosan fiber and explore the interactive effect by the response surface methodology(RSM).The experimental result(369.38 ± 1.61mg/g)was extremely close to prediction result(368.48mg/g)according to the response surface of method.(2)According to the result of fitting the isothermal adsorption data,the maximum Pd(II)uptake on SCF was as much as 426.93 mg /g in acid Pd(II)solutions,which is 3.43 times as much as the pure chitosan(124.65mg/g).In adsorption kinetics,Pd(II)rapidly adsorbed on SCF rapidly with the Pd(II)adsorption capacity reaching above 80% of the equilibrium adsorption capacity within 500 min,and achieving the adsorption equilibrium within 1400 min.The fitting result of pseudo-first-order model,pseudo-second-order model and intraparticle difussion model showed that higher fitting correlation coefficient was obtained from pseudo-second-order model.Futhermore,the predicted Pd(II)adsorption capacity of pseudo-first-order was closest to the actual test results.(3)Confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy,the amine group and Sulfur atom is proved to paticipate in the adsorption of Pd(II),wether hydroxyl group was just the frist crosslinker to enhance the molecular structure stability and acid resistance,instead of paticipating in the adsorption.(4)The study on the bed depth and inlet velocity of the column indicated that saturated adsorption capacity,Pd(II)removal rate and breakthrough time increased with the bed depth increased and decreased with inlet velocity increased.The BDST model could use the experiment data at the influent concentration of 300mg/L to predict the breakthough time when the influent concentration reduced to 200mg/L and the predicted time was very close to the actual breakthough.The fitting coefficient of Thomas model was always above 0.99 in different bed height and velocity of flow,which indicated that the Thomas model is applicative for fitting the breakthrough curve.(5)In the column system,SCF showed a large Pd(II)adsorption capacity(379.29mg/g)and high Pd(II)removal rate after three adsorption/dissorption cycles,which indicated that SCF had a good regeneration performance.A small volume of acid thiourea could desorp the Pd(II)within a short time to reach a high concentration multiple above 12,which indicated that acid thiourea solution showed a good performance for SCF regeneration to achieve recycling Pd(II)efficiently. |
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