Adsorption Of Nitrate And Phosphate By MTAB-modified Activated Carbon

With the increasing development of social economy,a large number of wastewater and sewage containing nitrate and phosphate were discharged into rivers and lakes,which resulted in serious eutrophication of water bodies.Therefore,it is significant to remove nitrate and phosphate from the water.Activated carbon,a good adsorbent,has been widely applied in the area of wastewater treatment while it did badly in adsorbing nitrate and phosphate.In this study,therefore,activated carbon was modified by Myristyltrimethylammonium bromide?MTAB?in order to enhance its adsorption capacity of nitrate and phospahte.First of all,the effect of different concentrations of MTAB was studied in this paper,which showed that the adsorption capacity of modified activated carbon for nitrate and phosphate was much higher than unmodified activated carbon,with the 6mmol/L best.In order to study the adsorption properties and mechanisms of MAC-6further,we also investigated the isotherm adsorption,adsorption kinetics tests of MAC-6.The effect of pH on adsorption capacity of nitrate and phosphate and its adsorption mechanisms were explored in this paper.Furthermore,the interferences between coexisting nitrate and phosphate,as well as the regeneration characteristics of MAC-6 were also discussed.The detailed results could be followed:To analyze adsorption of nitrate and phosphate by MAC-6,adsorption isotherm were used and fitted well with Langmuir adsorption model.According to the Langmuir adsorption model,in the situation pH=7,The maximum equilibrium adsorption capacity of MAC-6 for nitrate and phosphate was 29.85mg/g and 5.39mg/g respectively.In addition,the pseudo-second-order kinetic model was more suitable for describing the adsorption kinetics of MAC-6 for adsorbing nitrate and phosphate.That is to say that chemical adsorption is one of the adsorption mechanisms of MAC-6 for adsorbing nitrate and phosphate.The pH of the solution had a great effect on the adsorption of nitrate and phosphate by MAC-6 because the surface charge of MAC-6 and spieces of ions varied with the change of the pH of the solution.Generally speaking,the adsorption capacity decreased with the decreased pH.By analyzing the linear relationship between the amount of bromate released and phosphate absorbed or nitrate absorbed,it was found that ion exchange play a key role in adsorption of both nitrae and phosphate,with61%for NO₃^-,53%for H₂PO₄^-,88%for HPO₄^2-and 92%for PO₄^3-.Coexisting phosphate and nitrate in the solutions could indeed interfere with each other.With the increasing of concentration of interfering ions,mutual inhibition was more obvious.But the coexisting phosphate had played a weaker role than coexisting nitrate because nitrate could be more volunerbale to be absorbed than phosphate.It was found that MAC-6 still had good adsorption for both nitrate and phospahte after four cyclic adsorption-desorption experiments with NaCl solution,which indicated that MAC-6 had good adsorption stability.