Research On The Features And Mechanism Of Cation Pollutants Removal By Zeolites Synthesized From Coal Fly Ash

Early research results showed that compared with coal fly ash, zeolite synthesized from fly ash (ZFA) had very high cation exchange capacity (CEC). So, theoretically speaking, zeolite is one excellent material to remove cation pollutants from contaminated water. This research was initiated to investigate the application prospects of ZFA on sewage disposal by determining the properties of zeolite synthesized from fly ash on cation pollutants sorption as choosing the heavy metal cation Cr(â…¢) and eutrophic cation as the representative investigation objects.The Cr(â…¢) sorption capacities of fly ash and zeolite synthesized from fly ash were compared , and the properties and affecting factors of ZFAs on Cr(â…¢) sorption was investigated. The correlation of the amount of immobilized Cr(â…¢) with the chemical composition was also analyzed and the mechanism was discussed from the aspect of chemical reaction in solution. Finally the purification ability of ZFAs was investigated by using a real Cr(â…¢)containing water. The results showed that compared with coal fly ash, ZFAs had higher removal efficiency of Cr(â…¢) due to its higher CEC and acid neutralizing capacity (ANC). it is believed that the mechanism of Cr(â…¢) retention by ZFA involved ion exchange on zeolite surface, adsorption on oxides, especially Fe2O3d, and surface precipitation of chromium hydroxide. The retention of Cr(â…¢) via each of the mechanisms depends on pH, increasing with increased pH. The sorption maxima of Cr(â…¢) ranged from 22.29 to 99.91 mg/g for the 14 ZFAs. Ca ingredients (especially CaO and CaCO3) are vital for Cr(â…¢) uptake since it can elevate the pH value by determining the acid neutralizing capacity (ANC) of ZFAs. In the presence of NH₄⁺,Na⁺,K+,Ni²⁺ and Ca²⁺, ZFAs still exhibited high performances for the uptake of Cr3+ with low concentrations (<100 mg/L), showing very high selectivity for Cr(â…¢). Despite the complex composition of a real tannery wastewater, the removal rate of Cr(â…¢) by ZFAs with different calcium contents reached over 99% when the dosage of ZFAs is more than 5g/L . As to the high calcium ZFA, the removal rate was 96.97% when the dosage was 1.25 g/L. t is concluded that ZFAs may be promising materials for the treatment of Cr(â…¢)-containing wastewater.Based on early reseach on the properties and mechanism of ZFAs on ammonium removal, the influence of coexistence of a variety of cation interference (K⁺,Na⁺,Ca²⁺,Mg²⁺)on the ammonium removal efficiency by different exchangeable cation saturated ZFAs(Na⁺-ZFA,Ca²⁺-ZFA and Al³⁺-ZFA)was investigated. The experimental results showed that the influce of the four interferential cations was in the order: K⁺>Na⁺>Ca²⁺≈Mg²⁺. As the concentration of other cations increasing, the removal rate of ammonium by ZFAs get declined. Among the four interferential cations , K⁺ influenced the removal efficiency markedly , as which concentration rising from 2mmol/L to 16mmol/L the removal rate of ammonium by three ZAFs was 17.94%,62.61%,67.87% and 8%,0.06%,4.27% respectively. Besides, the removal experiments under the condition of natural water showed the result that the cations in natural water had little influence over the removal of the ammonium with the removal rate by Ca²⁺-ZFA and Al³⁺-ZFA over 80%. Therefore, the conclusion came that ZFAs has a good application prospect in the trearment of wastewater with low concentration of ammonium.