| A series of environmental problems had been brought by the rapid development of economy, especially water pollution. A great number of heavy ions and dyes had been observed in plenty of industrial waste water and posted potential threat to water and soil quality due to their high toxicity and non-degradable. In China, massive agriculture by-products with low cost are produced every year, however the phenomenon of irrational utilization in term of those resources has existed for a long period. So it is essential to study and develop the application in wastewater treatment. Herein, a novel method was conducted to modify wheat straw with epichlorohydrin and diethylenetriamine in order to obtain an efficient adsorbent to remove Acid Chrome Blue K(AK), Light Green(LG) and Cr(VI) from aqueous solution.The composition and structure of both natural wheat straw (NWS) and modified wheat straw (MWS) were characterized FTIR, XRD, XRF and elemental analysis. The results showed that there are different about the composition and structure between NWS and MWS. Adsorption quantity of MWS was significant higher than that of NWS. Adsorption quantity of NWS for AK, LG, Cr(VI) was found to be10,16,1.14mg/g, respectively, while in the same experimental, adsorption quantity of MWS was358,493,26.7mg/g, separately.The optimum condition for AK removal by MWS was as followed:adsorbent dosage0.8g/L, pH0-2.0, contact time360min; for LG system:adsorbent dosage1.0g/L, pH2.0～2.5, contact time360min; for Cr(VI) system:adsorbent dosage1.0g/L, pH2.0-3.0, contact time40min. There is not favor of adsorption when NaCl, CaCl2, MgSO4existed in solution. The best regeneration method for above-mentioned adsorption processes was0.01mol/L NaOH solution. The Radlke-Prausnitz, Redlich-Peterson and Koble-Corrigan isotherm models were used to correlate the equilibrium adsorption data of MWS-AK and all of those models fit the experimental data very well, The Pseudo-second-order equation and LJ equation were used to correlate the experimental data and those two kinetic models fit the experimental data very well. The lower value of Ea (23.0kJ/mol) showed that the adsorption process may be physical process. The Redlich-Peterson model was employed to analyze the equilibrium data of MWS-LG and gave excellent fitting degree to those data. The Pseudo-second-order equation and LJ equation were found to agree with experimental data very well. The higher value of Ea (45.9kJ/mol) showed that the adsorption process may be chemisorption process. Langmuir model was found to fit the MWS-Cr(VI) data quite well, the theoretic maximum adsorption capacity of Cr(VI) reached28.5mg/g. The Pseudo-first-order equation was selected to correlate the obtained experimental data and fit those data very well. The lower value of(18.6kJ/mol) showed that the adsorption process may be physical process. The negative value of Δ G was owed to the fact that the adsorption reaction was a spontaneous process, AH is negative which indicates the MWS-AK adsorption procedure is exothermic reaction, while Δ H is positive means that the MWS-LG and MWS-Cr(Ⅵ) process was a endothermic reaction.The adsorption potential of MWS to remove AK, LG, Cr(VI) from aqueous solution was investigated by using fixed-bed adsorption column. The effect of bed depth(2.0～5.0,1.1～4.0,2.5～10.6cm), flow rate(3.2-10.8,4.3～10.1,0.9～3.5ml/min), initial concentration of adsorbate(181-408,214-518,5.0～50mg/L) etc. on the breakthrough curves were discussed, the regeneration method was0.01mol/L NaOH solution. Three kintic models-Thomas, Yan and The Clark-were applied to experi-mental data to determine the characteristic parameters of the column. Thomas, Yan were found to be suitable for the description of the whole dynamic process. It can be concluded that MWS can be used to effectively remove the three pollutants from solution. |
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