Study On Preparation And Adsorption Properties Of Metakonlin-based Geopolymer Mcrospheres

Metakaolin is an amorphous powder material and it is easy to dissolve silicon aluminum monomer under alkaline conditions.After depolymerization and condensation reaction,a new environment-friendly material,geopolymer,with a specific three-dimensional network gel structure is formed.Geopolymers do well in adsorb and immobilize heavy metal ions,and have good separation effect for heavy metal polluted wastewater because of its special three-dimensional network condensation structure.What's more,geopolymers can be converted into zeolite under certain conditions.Zeolite also has many applications such as adsorption,which further expands the application scope of geopolymers.In this study,two kinds of spherical adsorbents were prepared from metakaolin by suspension dispersion solidification using water glass and NaOH solution as alkali activators.Optical microscopy,scanning electron microscopy?SEM?,X-ray diffraction analyzer?XRD?,transmission electron microscopy?TEM?,surface area and porosity analyzer?BET?and other characterization methods were used to characterize the two styles microspheres.?1?Water glass stimulated metakaolin to prepare geopolymer microspheres????MGMs?:MGMs were prepared by suspension dispersion and solidification method with water glass and metakaolin as main raw materials.The particle size distribution of MGMs could be controlled by adjusting the speed of stir and the temperature of silicone oil.Scanning electron microscopy?SEM?and adsorption experiments were used to determine the optimum technological parameters for pelletizing:speed of stir r=500 rpm,temperature of silicon oil T_c=60?C,water glass modulus=1.3 M,H₂O/Na₂O=19,Na₂O/Al₂O₃=0.8.The MGMs which prepared under these conditions have great adsorption performence on Cu²⁺,Pb²⁺,Ni²⁺,and the best adsorption effect is Pb²⁺which equal to 235.7 mg/g.?2?The MGMs adsorbents obtained under the optimum conditions were packed into fixed beds to adsorb Pb²⁺.The experimental results showed that the breakthrough time and saturation time were affected by different flow rates,different particle sizes of MGMs,different bed heights and different initial concentration of Pb²⁺.Low flow rate,small particle size of MGMs,high column height and low initial concentration of Pb²⁺are beneficial to prolong breakthrough time and saturation time.When flow rate is 2 mL/min,particle size of MGMs is in the range of 150-200?m,column height is 1.0 cm and initial concentration of Pb²⁺is 20 mg/L,the breakthrough time is 852 min,and the saturation time is 3360 min,which indicating that MGMs possess good durability.?3?NaOH solution stimulated metakaolin to prepare geopolymer microspheres???:Geopolymer microspheres???were prepared from NaOH solution and metakaolin by suspension dispersion solidification method.Geopolymer microspheres???with better sphericity by adjusting alkalinity of slurry and they can be transformed into zeolite via changing curing temperature and curing time.Scanning electron microscopy?SEM?and X-ray diffraction?XRD?were used to characterize the microspheres??? and determined the process parameters of transforming geopolymer microspheres???into NaA-zeolite microspheres?NaA-ZMs?:speed of stir r=500 rpm,curing temperature T_c=80?C,curing time t_c=48 h,slurry alkalinity=23%.NaA-ZMs prepared under these conditions have great adsorption effects on Cu²⁺,Pb²⁺,Ni²⁺.Batch adsorption experiments showed that the adsorbent had the best adsorption effect on Pb²⁺with adsorption capacity of 546.6 mg/g.The adsorption rate was the fastest in the first two hours,and reached equilibrium after 10 h of adsorption.Under appropriate conditions,the maximum adsorption capacity of NaA-ZMs for Pb²⁺reached 584 mg/g,and the removal rate reached 99.99%.The adsorption process well fitted with pseudo-second-order kinetics model,Langmuir model and D-R model,which respectively demonstrates that it is a favorable adsorption for both chemical adsorption and ion exchange.?4?The NaA-ZMs were packed into a fixed bed to adsorb Pb²⁺.The experimental results show that different particle sizes of NaA-ZMs have different diffusion resistance.Small particle size of NaA-ZMs,low flow rate,high bed height and low initial concentration of Pb²⁺are beneficial to prolong the breakthrough time and saturation time.When the flow rate is 2 mL/min,the particle size of the NaA-ZMs is in the range of 125-300?m,the column height is 5.0 cm and the initial concentration is 11.9 mg/L,the breakthrough time of NaA-ZMs adsorbing Pb²⁺is 5160 min,which indicating that NaA-ZMs has good durability.Moreover,the effluent concentration of NaA-ZMs meets the emission standard and the removal rate is as high as 99.9%.Under appropriate experiment conditions,the maximum adsorption capacity of NaA-ZMs for Pb²⁺is 880.8 mg/g,which is 3.6 times as much as MGMs?246.4 mg/g?.