Improvement Of Pollutants Removal Capacity Of Synthesized Zeolite By Salt Treatment

Zeolite has been widely used in environmental engineering field to solve the pollutants problems and it's a mineral resource with great potential in the future. Much work has been done on synthesized zeolite in our lab. The results have shown that zeolite synthesized from fly ash (ZFA) has a large cation exchange capacity (CEC) and phosphate immobilization capacity (PIC). Theoretically, it's an excellent material with the capacity of removing ammonium and phosphate simultaneously. However, ZFA without modification was not efficient for purification of ammonium and phosphate at low concentrations occurring in real effluent. In addition, it has a low capacity of removing oraganic pollutants in water.In the present research, ZFA is pre-treated with inorganic metal salt and cationic surface-active agent in order to enhance the removal efficiency of ammonium, phosphate and organic pollutants at low concentrations. We also studied the effects of several common ions and seawater electrolytes on phosphate removal efficiency to evaluate the potential of application in real effluent.The treatment of inorganic metal salt on ZFA showed that ZFA treated with appropriate cation (Al³⁺,Ca²⁺)significantly improved the removal efficiency of ammonium and phosphate at low concentrations, having a great potential to be used in sewage disposal and prevention eutrophication.Secondly, The effects of several common ions (SO₄^2-,HCO₃^-,NO₃^-,SiO₃^2-,Ca²⁺,Mg²⁺) on phosphate removal from aqueous solution by ZFA were studied. The results show that, compared with pure water, presence of NO₃^- (NaNO₃) and SO₄^2-(Na₂SO₄) increased the phosphate removal by ZFA while HCO₃^- (NaHCO3) remarkably inhibited phosphate retention. In the case of SiO₃^2- (Na₂SiO₃), nevertheless, it facilitated the phosphate removal for Ca-ZFA but notably abated the adsorption of phosphate by Al- and Fe-ZFA due to the dramatic rise of equilibrium pH. Presence of Ca²⁺ caused a significant increase of phosphate removal by ZFA while existence of Mg²⁺ has positive effect for Al- and Fe-ZFA and has negative effect for Ca-ZFA. Based on the typical concentrations of the ions in water/wastewater, it is deemed that Ca²⁺ and HCO₃^-/CO₃^2- would have the greatest influence on phosphate uptake by ZFA, with the former having positive while the latter having negative effects.Thirdly, the influence of seawater electrolytes on sorption of phosphate by zeolite synthesized from fly ash (ZFA) was investigated. The results showed that Al- and Fe-ZFA showed nearly complete removal for phosphate, regardless of the major seawater electrolytes, the pH, and the salinity. For Na-, Mg-, and Ca-ZFA, a dependence of phosphate removal on the kind and the concentration of marine electrolytes as well as the pH of the system was observed. The mechanism for phosphate removal by Ca-ZFA, Mg-ZFA, and Na-ZFA was mostly precipitation. Therefore, in most cases, presence of oceanic electrolytes containing divalent cation (Ca²⁺/Mg²⁺) enhanced the phosphate removal performance. On the whole, the presence of seawater electrolytes had roughly no or even positive effects on the removal of phosphate by ZFA.At last, we come to the conclusion that ZFA pre-treated with organic agent showed a great enhance in the removal capacity of phosphate and phenol. The basic and acidic pH condition is favorable for phosphate removal. The isothermal adsorption curves fit the Langmuir type, showing a typical chemical adsorption. Also, the phenol removal rate was greatly improved after treatment. The favorable pH is basic range.The main mechanism of phenol removal is organic distribution and electrostatic adsorption. At the same time, the treated ZFA still keeps the high ammonium removal capacity so that it shows the potential of being widely used in real effluent.