Preparation Of Hydrotalcite Precursor By Mechano-chemical Method And The Promoted Adsorption Capacity

With the rapid development of industry,more and more organic wastewater are discharged annually.Due to its complex ingredients and high hazard,organic wastewater is regarded as a concern to environmental protection.Adsorption is a common method for organic wastewater removal.Therefore,it is essential to find an adsorbent that can effectively remove organic wastewater at a high sorption capacity.Layered double hydroxides?LDH?,as a new kind of inorganic materials,have potential value in different industries,such as catalysis,anti-flocculation,medicament,and wastewater treatment,owing to their unique eletro-kinetic property and layered structure.In this paper,a mechanochemical method was used and a new concept of precursor was introduced to promote its adsorption capacity with dye,phenol and paranitrophenol as adsorbate target.The main study contents were listed as follows:?1?Mg?OH?₂ and Al?OH?₃ as starting materials were used to synthesize the amorphous precursor.LDH phase was easily obtained by stirring the precursor samplein water at room temperature.The samples were characterized by a set of analytical methods including X-ray diffraction?XRD?,thermo-gravimetry/differential scanning calorimetry?TG–DSC?,scanning electron microscopy?SEM?and Fourier-transforminfrared?FT–IR?.The results showed that 1h grinding of Mg?OH?₂first and then cogrinding with Al?OH?₃ for another 3 h allowed the synthesis of precursor and agitation in water for 5 h allowed the synthesis of LDH sample.?2?The use of the precursor and LDH as adsorbents to remove methyl orange,a model anionic dye,from aqueous solution was investigated in terms of adsorbent dosage,temperature,dye concentration,and contact time.Dispersing only the precursor in aqueous solution with methyl orange at room temperature enabled the in situ adsorption of the adsorbate during the synthesis of LDH.When the dosages of the precursors and LDH were 0.6 g/L at 25?,the maximum removal efficiencies were 98.2%and 62%for the dye concentration of 100 mg/L.The adsorption of methyl orange on adsorbent reached equilibrium within 3 h.The obtained maximum methyl orange adsorption capacity on the precursor sample was 1110.2 mg/g,which is much higher than that by the LDH sample?467.3 mg/g?.Besides,the adsorption kinetic of methyl orange onto the precursor and the LDH sample was found to match the pseudo-second-order model.?3?The removal of two phenols?phenol and paranitrophenol?from aqueous solution was investigated using the precursor and the LDH,in terms of adsorbent dosage,concentration and contacting time.When the dosage of the precursor was 4 g/L,the maximum removal efficiencies were 98%and 66%for the paranitrophenol and phenol concentration of 50 mg/L.The precursor exhibited high adsorption ability in the same concentration solution with all the ranges of the used adsorbent dosage.The sorption kinetics of phenol and paranitrophenol were well described by the pseudo-second-order model.The adsorption isotherm for phenol and paranitrophenol fitted the Langmuir model.The maximum removal capacities for paranitrophenol were 356.4 mg/g by the precursor sample,which is much higher than that by the LDH sample?82.55 mg/g?.To sum up,the precursors can be synthesized by mechanical ball milling.Dispersing only the precursor in aqueous solution with target adsorbate at room temperature enabled not only in situ adsorption of the adsorbate together with the synthesis of LDH adsorbents but also significantin crease in removal efficiency,much higher than that by the normal adsorption of a synthesized LDH product as adsorbent.Moreover,no intermediate pollutants were produced during the whole process.Engineering application may be expected from the easy preparation of such precursor as adsorbent to purify the tremendous amounts of organic wastewater.