Synthesis Of Different Morphologies Of Fe₃O₄ Composite With Kaolin And The Adsorption Property Of Cu²⁺

With the incessant development of industrial technology,the problem of heavy metal pollution has increasingly become one of the most serious problems in environmental protection issues in recent years.The industrial effluent discharged from China is about 20 billion tons every year and the direct economic loss caused by it exceeds 20 billion RMB.These industrial wastewater contain a large amount of heavy metal ions,among which the copper-containing waste water mainly comes from copper mining,copper electroplating,dyeing and electronics.In the device manufacturing industry,these copper-containing wastewater are seriously endangering environmental quality and human health through soil and groundwater.According to the National Sewage Comprehensive Discharge Standard,the maximum allowable concentration of Cu²⁺is 0.5 mg/L,so it is cost-effective.Adsorption materials are playing an important role in the treatment of heavy metal wastewater.Kaolin is one of inorganic mineral clay,which has been widely used in heavy metal adsorption due to its abundant reserves,low cost,and good heat resistance.However,kaolin is easily to be suspended and dispersed in water to form secondary pollution due to fine particles.It can be composited with triiron tetraoxide to produce magnetic composites.It not only can obtain good adsorption performance but also can be recovered through magnetic separation.The adsorption of heavy metals was realized by post-recovery and it can solve the problem that is difficult to recover kaolin after adsorption.In this paper,the natural mineral kaolin was used as raw material and Fe₃O₄ were coated on the surface of kaolin through oxidation-precipitation technique.Firstly,the effects of different oxidants used to prepare Fe₃O₄/kaolin and their morphology were tested.The adsorption capability of Cu²⁺on Fe₃O₄/kaolin was compared.The results showed that Fe₃O₄/kaolin composites had the best removal ratio of Cu²⁺when KNO₃was used as oxidant.The equilibrium adsorption capacity of Cu²⁺was 5.40 mg/g,which was about as 5.7 times as that of kaolin.Therefore,KNO₃ was chosen to be used as oxidant to prepare Fe₃O₄/kaolin magnetic composites in the follow-up experiments.The effects of different concentrations of NaOH on the morphologies and properties of Fe₃O₄/kaolin composites were investigated.The morphology,structure and adsorption mechanism of Fe₃O₄/kaolin were measured by SEM,XRD,BET and FTIR techniques.The equilibrium adsorption capacity of Cu²⁺was 14.97 mg/g if being fixed with the concentration of NaOH as 10 mol/L.Meanwhile,the composite can be quickly recovered by an external magnetic field.Under the optimal reaction conditions for the determination of Fe₃O₄ production,exfoliated flake kaolin was prepared by ball-milling.The best ball milling time was 4 h which was determined by a laser particle size analyzer.Then Fe₃O₄/kaolin was prepared with different amount of kaolin.The best equilibrium adsorption capacity of Cu²⁺was17.98 mg/g after introducing 3 g of kaolin into Fe₃O₄.Based on the above results,the magnetic properties of the best specimens were characterized by VSM.The results showed that the saturation magnetization value of Fe₃O₄/kaolin was 16.19 emu/g,and the coercivity was almost zero.This can help achieving rapid recovery under magnetic field.The adsorption mechanism was performed by using the Langmuir and Freundlich sorption isotherm models.The adsorption performance of Fe₃O₄/kaolin magnetic composites to Cu²⁺was conformed to the two models,which had the ultimate theoretical adsorption capacity of Fe₃O₄/kaolin to Cu²⁺was 38.26 mg/g.It illustrated that the adsorption behavior of Fe₃O₄/kaolin composite included both monolayer and multiple molecular layers.