Adsorption Of Acid Dyeing Wastewater With Zn Based Layered Double Hydroxides And Their Calcined Products

Textile, printing and dyeing industries develop rapidly, which make the quantity of dyeing wastewater increasing and the problem of environmental pollution more and more serious. And it is necessary to adsorb the acid printing and dyeing wastewater for treating the wastewater and protecting the environment, this wastewater is one of the most difficult of wastewater pollutants to remove. Low Adsorption capacity, high cost, and secondary pollution are the major shortcoming for the traditonal sorbent. Therefore, in the paper, layered double hydroxides(LDHs) are used as an sorbent with large surface area, adjustable layer board, exchangeable interlayer, "memory effect" of structure, etc. The adsorption capacity of LDHs is improved by changing the ratio and kind of layer board cation and calcining. Then, we select the best sorbent to adsorb Acid Yellow 17(AY17), Acid Red 14(A14) and Crystal Violet(CV), and research the best adsorption conditions. Combined with the result of experiment and the calculation of Materials Studio, the adsorption mechanism is predicted.(1) Different binary Zn based hydrotalcite(Zn3Al-LDHs, Zn3Cr-LDHs) and their calcined products were as an sorbent to adsorb Acid Yellow 17(AY17). The results indicated that calcined Zn3 Al Layered double hydroxides(Zn3Al-CLDHs) had high adsorption capacity, under the optimum adsorption condition(25 ℃, p H = 7), more than 98% of AY17 on C0 = 50~200 mg·L-1 was absorbed by 50 mg of Zn3Al-CLDHs. The sorbents were chracterized by ICP, XRD, FT-IR and UV-Vis DRS. The kinetics and thermodynamics of the adsorption process were further explored, finding that the sorption process were fitted with the Langmuir, Freundlich isotherm model and second-order kinetics model. In addition, based on the analysis of chracterization and experimental data, we assume that film diffusion and intraparticle diffusion play important roles in the possible mechanisms.(2) Different binary Zn based hydrotalcite(Zn3Al-LDHs, Zn2Cr-LDHs, Zn3Cr-LDHs, Zn4Cr-LDHs) and their calcined products were as an sorbent to adsorb Acid Red 14(AR14), the influences of trivalent cations and Zn Cr mole ratio were also studied. The results indicated that the optimum sorbent was Zn3Cr-LDHs, the maximum adsorption capacity for AR14 was 484.63 mg·g-1. Meanwhile, lower p H value and higher temperature were favorable to the removal of AR14. The sorbents were chracterized by ICP, XRD, FT-IR and BET. The kinetics and thermodynamics of the adsorption process were further explored, finding that the sorption process were fitted with the Freundlich isotherm model and second-order kinetics model. In addition, based on the analysis of Materials Studio simulation, the adsorption menchanism was that AR14 were adsorbed on the surface of Zn3Cr-LDHs, the-SO3- group was the reaction point.(3) Ternary Zn based hydrotalcite(Zn Mg Fe-LDHs) and its calcined products were as an sorbent to adsorb Crystal Violet(CV), the kinetics and thermodynamics of the adsorption process were also discussed. The results indicated that calcined Zn Mg Fe Layered double hydroxides(ZMFO) had good adsorption capacity. The effect of temperature, pH and sorbent amount on the adsorption of CV was further studied. With increasing initial p H and temperature, the adsorption amount increased, the reaction time decreased, and the adsorption removal efficiency was still 78.46% after recycling 3 times; the optimum sorbent amount was 50 mg. The sorbents were chracterized by XRD, FT-IR and UV-Vis DRS. The adsorption process can be well fitted with the Langmuir and second-order kinetic equation, it is spontaneous and endothermic.