RESUMO
Characteristics of simultaneous removal of ammonium and phosphate from wastewater by zeolite synthesized from fly ash was investigated. The amount of ammonium and phosphate removed by zeolitized fly ash changed with time, and approached to a constant value after adsorption time of 24h was reached. The amount of ammonium and phosphate removed also increased with the rise in the amount of zeolite added, but slackened above the solid/liquid ratio of 8 g x L(-1). The removal rate of ammonium by zeolitized fly ash could rise to the maximum value of 60% when pH was between 7 and 9, and declined out of the pH range. For phosphate, minimum removal rate of about 85% was obtained within pH 7-9, and the removal rate increased to about 100% out of the pH range. The adsorption of ammonium on zeolitized fly ash was an exothermic reaction; the removal rate of ammonium could decrease with the rise in temperature. On the contrary, the adsorption of phosphate was an endothermic reaction, and the rise in temperature favored the removal of phosphate by zeolitized fly ash. The adsorptive ability of ammonium on zeolitized fly ash was: Al-Z > Mg-Z > Ca-Z > Na-Z > Fe-Z. The order for phosphate was: Al-Z > Fe-Z > Ca-Z > Mg-Z > Na-Z. It was proposed that the mechanism for the removal of ammonium from wastewater by zeolitized fly ash was cation exchange process, while the mechanism for phosphate was not only the precipitation reaction of phosphate with cation in solution, but also adsorption mechanism.
