Preparation Of Modified Adsorbent And Its Adsorption Study Toward Metal Ions And Organic Matters From Aqueous Solution

Purified terephthalic acid(PTA),which is an important chemical raw material,has beeb widely used in polyester and many other chemical industry.There is a large amount of wastewater produced in PTA refine unit.The wastewater contains not only organic pollutant(TA,P-TOL,BA)but also organic ones such as Co(II)and Mn(II).Extraction-ultrafiltration-reverse osmosis-adsorption technology is developed by our research team for the preliminary treatment of wastewater.Firstly,PX,which is the material of PTA,is applied to extract most organic matters from the water.Secondly,metal ions in the aqueous solution can be recycled successfully by appealing to ultrafiltration-reverse osmosis-adsorption craft.However,little PX is remained in water after extraction.Since the major material of the reverse osmosis membrane is polyamide,which would be dissolved easily in PX and then shortens the stabilization of the whole craft seriously.Therefore,removing the little quantity of PX from the wastewater before ultrafiltration-reverse osmosis may generate crucial significance for extraction-ultrafiltration-reverse osmosis-adsorption technology for industrial application.Adsorption is one of the most effective methods for removing small quantity of contaminants from effluents.Adsorption technology has been employed triumphantly in medicine,printing and dyeing industry for treating wastewater.In this paper,Na-Bentonite was used to adsorb metal ions and organic matters.Different parameters,such as dosage of adsorbent,adsorption time and pH were investigated during the adsorption process.And the results indicated that the removal adsorption efficiencies of Co(II)and Mn(II)were above 95%when dosage of Na-Bentonite was 3g-L-1.Equilibrium situation was achieved within lOmin.It's beneficial for adsorption process with pH increased.As for PX,the removal rate was only about 80%when the adsorbent concentration was 12g-L-1,equilibrium time was 120min,and pH had trivial effect on the adsorption process.Metal ions were much more easily adsorbed onto Na-Bentonite than PX,for the selectivity coefficients of Co(II)versus PX and Mn(II)versus PX were 0.03 and 0.09 respectively.In addition,the adsorption thermodynamics research discovered that,equilibrium data of metal ions onto Na-Bentonite agreed with the Langmuir equation well,while the PX agreed with the Freundlich formula.The adsorption process of either metal ions or PX is spontaneous,and it's an endothermic and entropy increasing process as well.Based on the investigations of the adsorption characteristics and adsorption rule of Na-Bentonite adsorbing metal ions and PX,a series of modified means for Na-Bentonite were carried out effectively,so as to single out an adsorbent whose adsorption property was intense for PX and feeble for metals.To be sure that,the desired novel adsorbent(C/A-Bentonite)was invented using cationic surfactant,namely hexadecyl trimethyl ammonium bromideand 2-mercaptoethylamine hydrochloride to modify the natural Na-Bentonite.The PX removal efficiency surpassed 85%,whereas the metal ions was less than 10%when the C/A-Bentonite concentration was 6g L-1.Results also showed the adsorption capacity of PX increased from 0.2mg.g-g to 6mg·g-1,while Co(?)and Mn(?)dropped to 3mg·g-1 from 17mg·g-1 and 17mg·g-1?respectively.Further exploration was carried out using C/A-Bentonite to deal with the Co(?),Mn(?)and PX.The conclusions manifested that PX was superior to be adsorbed onto C/A-Bentonite at various operation conditions.At the real wastewater(pH=3),the selectivity coefficient of PX versus Mn(II)increased to 70.02,PX versus Mn(?)was 171.69.Therefore,PX can be removed selectively from the organic and inorganic matters coexisting system when pH of the solution was appropriate.Moreover,the main removal mechanism of metal ions and PX onto adsorbent was discussed,and the relationship between the structure of the adsorbent and adsorbents was explored using modern analytical techniques,including IR,XRD,BET and SEM.The results manifested that the main mechanism of metal ions and PX adsorbed onto adsorbent were different.The force of Na-Bentonite adsorbing metal ion was attributed to ion exchange,namely,the cations from aqueous solution are replaced by the ions exited in the interlamination of bentonite.For PX,the force is due to the surface physical aggregation.While,the main mechanism of PX adsorbed onto C/A-Bentonite can be explained by two reasons:one is physical absorption,and the other one is that PX was dissolved into surface-active agent.