Synthesis Of Magnetic Modified Bentonite Adsorbents And Its Application

Montmorillonite is the essential component of bentonite,which has a special structure and unique properties.So much attention has been paid to water purification and wastewater treatment.Montmorillonite content of natural bentonite generally varies from 50%to 80%,or even lower.But the content was usually required at more than 90%in the practical application.Therefore the purification and examination of bentonite are very important.Bentonite can also be studied to play a greater role in environmental protection.In this work,we reported various modified methods for bentonite and discussed its application in organic wastewater treatment.Currently,the montmorillonite content is calculated by the equation of methylene blue value of adsorption.But,the equation isinaccurate when we determine some high-purity samples.Montmorillonite content（M）is obtained using the fitting of Rietveld full spectrum fromXRD.The experimental results are convicted,However,this experiment is very tedious.Thus,we modify the formula for methylene blue value of adsorption（MBT）by GSAS procedure usingthe fitting of Rietveld full spectrum from X-ray diffraction,Six bentonite samples are analyzed and the methylene blue value of adsorption equation is also well modified.The results was are obtained as follow:when the MBT<40g/100g,the formula is unchanged;when MBT>40g/100g,the equation is:M = 0.0462×eMBT/8.4642+83.8176.Furthermore,by comparing the various purification methods and sodium replacement methods,the raw bentonite was purified using the wet purication,and the optimum results are list:ratio of water and bentonite is 15:1;（NaP03）6 is the best dispersant,its concentration is 0.2%;pH =7-8;thesedimentation time is 50 min;the centuifuge speed is 1000 r/min.In addition,some sodium agents and organic modifiers were used to modify bentonite.It’s found that hydrophobic bentonite and long carbon chain organic bentonite favored adsorb organic pollutant.The effect of interlayer charge on the adsorption properties of the bentonite could be examined by the CEC of bentonite,and when CEC at 62 mmol/100 g would effectively adsorb phenol.Although lots of modified bentonites have been applied in organic wastewater,but magnetic Fe304 modified bentonite composites has a little report.Here the magnetic Fe₃O₄/bentonite nanocomposites were prepared by a chemical coprecipitation method and used as adsorbent for methylene blue（MB）removal.The characterization revealed that the pore volume and average pore size of magnetic Fe304/bentonite nanocomposites were larger than Fe304 and bentonite.The optimum conditions of methylene blue removal were obtained as follows:the original pH of methylene blue is 7.37,contact time is 25 min,the reaction temperature is 20 ℃,the methylene blue concentration is 120 mg/L,magnetic Fe304/bentonite nanocomposites dosage is 2.5 g/L.A pseudo-second-order adsorption model fits well with the experimental data.The equilibrium adsorption isotherm follows a Langmuir model（qm = 106.38 mg/g）better than Freundlich or Temkin model.Fe₃O₄-bentonite/H₂O₂ heterogeneous Fenton system to degrade methyl orange wastewater was further established,the reaction can achieve equlibrium at 20 min,and the decolorization rate was 96.72%.Comprehensive consideration the equilibrium time and decoloring rate of the Fe₃O₄-bentonite/H₂O₂ system,which was better than that of Fe₃O₄,H₂O₂,Fe₃O₄/H₂O₂,magnetic bentonite systems.The best reaction conditions determined by single factor experiments were obtained as follows:the initial pH is 3,Fe₃O₄-bentonite dosage is 0.5 g/L,the amount of H₂O₂ is 0.05 mol/L,the initial concentration of methyl orange is 100 mg/L,the reaction temperature is 40 ℃,the best decolorization of methyl orange is obtained.Due to the special structure of methyl orange,the range of pH had no obvious widen.After 5 recycles of Fe₃O₄-bentonite,the decolorization rate remains as high as 89.94%.And compared with Fe₃O₄-bentonite addition amount,the quantity of iron ion dissolution can be negligible,as it was only 3.23×10-3 mg/L after 60 min reaction,which illustrating that Fe₃O₄-bentonite had better catalytic activity and higher lifetime.These results prove that the design and production of modified bentonite with magnetic properties are becoming very attractive and are beginning to find applications in the fields of dyeing wastewater treatment.