Preparation Of Stimuli-Responsive Microgels And Its Hexacyanoferrate（HCF） Composite Adsorbent For Treatment Of Cu²⁺ And Cs⁺ Wasted Water Via Flotation

The development of industry plays an important role in promoting the economy,but industrial metal wastewater has a huge potential threat to the ecological environment,so metal wastewater must be strictly treated,otherwise it will endanger the living environment and health of human beings.The discharge of industrial wastewater contains high concentrations of heavy metals.Among them,metal copper,which has low economic cost and is widely used,is already toxic when it exists in a relatively low concentration in an aqueous solution.In addition,the discharge of nuclear industry wastewater has gradually increased with the development of new energy sources.The wastewater contains highly radioactive elements,among which ¹³⁷Cs,the main radioactive pollution element,has a long half-life and exists in the form of positive monovalent Cs⁺in aqueous solutions.Both Cu²⁺and Cs⁺water bodies have high water solubility,non-biodegradability,and can destroy the food chain through biology,thus threatening human health.Therefore,this paper mainly takes the removal of Cu²⁺and Cs⁺as an example to further study the treatment of industrial wastewater.By investigating the advantages and disadvantages of different treatment methods and adsorbents,a strategy for the adsorption of copper and cesium by stimuli-responsive microgel-based composites was proposed.First,on the basis of temperature-responsive p NIPAM microgels,we designed the copolymerization of 1-vinylimidazole（1-VIM）monomers which the Cu²⁺-sensitive,to prepare temperature-sensitive poly N-Isopropylacrylamide-vinylimidazole（poly（NIPAM-co-VIM））（PNV）microgels.The composition and microscopic morphology of the samples were determined by Nuclear magnetic resonance（NMR）,Scanning electron microscopy（SEM）,Dynamic light scattering（DLS）and other characterization methods,which confirmed that the prepared microgels were temperature responsive.Then,the effect of Cu²⁺on the temperature responsiveness and particle structure morphology of PNV microgels was studied by DLS and Static light scattering（SLS）,and was found that the complexation of Cu²⁺with the imidazole groups of VIM segment can soften the PNV microgels and improve the performance of the PNV microgels.Particle homogeneity,which in turn enhances the swelling of PNV microgels,shifts its volume phase transition temperature（VPTT）to high temperatures.The temperature responsiveness of PNV microgels can be regulated by Cu²⁺and exhibited selectivity.Then,Pickering foam was prepared by PNV dispersion and its stability was studied.It is found that the foam have obvious temperature responsiveness:it is super stable below VPTT and rapidly destroy above VPTT,and the temperature responsiveness can be regulated by Cu²⁺concentration.Foam perform super stable at a certain temperature in the presence of Cu²⁺,while other competing ions(such as Mg²⁺,Zn²⁺,Na⁺)are difficult to stabilize the foam,which indicates the possibility of selective separation of Cu²⁺by PNV microgel-based froth flotation method.The interfacial behavior of the microgels at the gas-liquid interface shows that the PNV microgels have good interfacial activity and thus had good foaming properties.The excellent interfacial shear viscoelasticity of the PNV complexed with Cu²⁺can resist foam coalescence,thereby ensuring the super stability of the foam.In order to explore the selective recovery performance of the prepared PNV2 microgels for Cu²⁺,we compared the Cu²⁺adsorption capacity of the PNV microgels in pure Cu²⁺solution and copper-containing solution containing competing ions(Mg²⁺,Zn²⁺,Na⁺)by Inductively coupled plasma optical emission spectrometry（ICP-OES）.It is found that under the interference of competing ions,the adsorption capacity of PNV on Cu²⁺is decrease,but it still have good selective adsorption while the adsorption selectivity Kd of the microgel for Cu²⁺reached268.3 m L/g.Therefore,the prepared PNV2 microgels not only have the performance of selective recovery of Cu²⁺,but also can act as a responsive stabilizer for froth flotation.Finally,we designed a thermosensitive composite material of microgel/potassium copper ferrocyanide（PNV-KCu HCF）for the treatment of cesium-containing wastewater.The Cu²⁺was immobilized in the PNV microgel by the copper-imidazole complex reaction,and then K4[Fe（CN）6]was introduced to grow KCu HCF nanoparticles in situ to obtain the target product PNV-KCu HCF composite microgel.The target product was successfully synthesized by Malvern particle size analyzer（zeta-sizer）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）and other characterization methods,and it was still temperature responsive.The adsorption capacity of PNV-KCu HCF for cesium ions was measured by ICP-OES up to 136 mg/g（PNV-KCu HCF,25°C,[Cs⁺]0=300 ppm）,and under the interference of high concentrations of Na⁺（1 mol/L）,there was still an effective adsorption capacity of 75.4 mg/g.In order to prove the possibility of recovering the Cs⁺adsorbed PNV-KCu HCF composite adsorbent by froth flotation,we recorded the change of froth with time and temperature.The results were as expected,the foam stabilized by PNV-KCu HCF microgel had good foamability and stability at room temperature,and with the increase of temperature,the foam became unstable and gradually burst.