Adsorption Investigation Of APTMS-DTPA/PVDF Chelating Membrane Towards Nickel Ions

Using the combined technique of the solution blending and phase inversiontechniques, a modified polyvinylidene fluoride-based chelating membrane, namely, the3-aminopropyltrimethoxysilane-diethylenetriaminepentaacetic acid/polyvinylidenefluoride （APTMS-DTPA/PVDF） chelating membrane was prepared for the removal ofNi（Ⅱ） in different forms from the wastewater. The components of the cast solution used toprepare the membrane, were optimized by the orthogonality experiment.The chelating membrane was characterized by SEM, TG-DTA, XRD, FTIR and（13）^CNMR techniques, and the ion exchange capacity, zero charge point, mean pore diameterand porosity, moisture content and pure water flux of the membrane were also measured.The effects of different controlling parameters, such as solution initial pH, temperatureand contact time, metal ions initial concentration, on the adsorption performance of thechelating membreane were investigated. The effects of the coexistent cations involvingNH₄⁺, Ca（Ⅱ） and Fe（Ⅲ）, and the organic acids including lactic acid, succinic acid, citricacid on the Ni（Ⅱ） uptake of the membrane were studied. Quantitative adsorptionexperiments were performed for elucidating the adsorption characteristics regarding thepresence of coexistent cations and the organic acids. The influences of Fe（Ⅱ）, Co（Ⅱ）,Cu（Ⅱ） and Zn（Ⅱ） on Ni（Ⅱ） uptake of the membrane in the ternary nickel plating effluentswere also taken into account. Furthermore, membrane filtration experiment was alsoconducted. The adsorption/desorption properties of the modified PVDF chelatingmembrane were also studied.The results illustrate that the modified PVDF membrane has a microporous structureand exhibits an excellent thermal stability. The polyaminecarboxylate groups for chealtionhave been blended to PVDF membrane successfully. The zero charge point and the ionexchange capacity of the chelating membrane are6.7and3.2mmol/g, respectively, whichindicates that the chelating membrane has a strong capacity of adsorption. The batchadsorption results show that the sorption kinetics fit well to Lagergren second-orderequation and the isotherms can be well described by Langmuir model. D-R plots indicatethe adsorption process is the ion exchange reaction. The thermodynamic parameters ΔG⁰<0、ΔH⁰<0、ΔS⁰>0, demonstrate the spontaneous and exothermic nature of theadsorption. The coexistent cations interfere with the Ni（Ⅱ） adsorption in the order ofCa（Ⅱ）>NH₄⁺>Fe（Ⅲ）. The complexing capability of the organic acid is in the order oflactic acid <succinic acid <citric acid. The coexistence of Ca（Ⅱ） and NH₄⁺exhibits aslightly antagonistic effect on Ni（Ⅱ） uptake, and the coexistence of succinic acid and citricacid shows an enhanced interference on the adsorption. However, the interference of citricacid is not notable when it coexists with Ca（Ⅱ）. The adsorption study indicates that thecoexistent cations and organic acids only exert the influences on reaction rate and theadsorption capacity, they do not change the essence of the adsorption. In the ternary nickelplating wastewater, the influence of the coexistent cations on the Ni（Ⅱ） adsorption is in theorder of Zn（Ⅱ）<Co（Ⅱ）<Fe（Ⅱ）<Cu（Ⅱ）, indicating the remarkable influences of them onNi（Ⅱ） uptake. The adsorption/desorption experiment indicates that the chelatingmembrane possesses an excellent property of reuse.