Ammonium Removal From Aqueous Solutions By Zeolite Adsorption Together With Chemical Precipitation

As China's industrial development, ammonium wastewater has become one of the industrial wastewater which is difficult to deal with. High concentration of ammonium can make the water black and smelly. It can also produce strong carcinogenic nitrosamine and do harm to human health. Excess ammonium will also lead to eutrophication and destruction of ecological balance of the water body. Therefore, it is urgent to find feasible methods to deal with ammonium wastewater.In this paper, the wastewater was prepared by NH4C1 and deionized water. The initial NH4+-N concentration of the wastewater was 100 mg L-1. Ammonium was removed from the wastewater by zeolite adsorption together with chemical precipitation. Morphologies and structures of zeolites were analyzed by different means. At first, zeolite particle size, contact time, zeolite amount and rotate speed were explored in the experiment of ammonium removal by natural zeolite. Then, modification time, concentration, temperature, amount and type of solution were explored in the experiment of ammonium removal by pretreated zeolite. Adsorption isotherms and breakthrough curve for adsorption of NH4+-N by pretreated zeolite was determined too. At last, zeolite was regenerated and ammonium of regeneration solution was removed by chemical precipitation. Solution pH, phosphorus and nitrogen ratio, magnesium and nitrogen ratio were explored in the experiment of ammonium removal by chemical precipitation.Using 4.0 g natural zeolite (40 mesh) to deal with 100 mL ammonium solution at 20℃and 180 rpm, the ammonium removal efficiency was 30.73%. Modification of natural zeolite by sodium salt could improve ammonium removal efficiency evidently and NaCl was the best salt. The optimal modification conditions were as follows, time:3 h, concentration of NaCl solution:60 g/L, temperature:70℃, amount: 25 mL solution/g zeolite and the ammonium removal efficiency was 85.55%. Both Langmuir and Freundlich isotherms provided good fit to the experimental data of ammonium adsorption on NaCl-treated zeolite, but Freundlich isotherm was better. The maximum adsorption capacity of zeolite for NH4+-N was 22.38 mg/g. In the column experiment, breakthrough capacity of zeolite for NH4+-N was 3.36 mg/g and BV was 41. The NaCl-treated zeolite regeneration efficiency was 88.37%. The optimal chemical precipitation conditions were as follows, pH=9.5, P:N=1:1, Mg:N=1.2:1. Chemical precipitation reduced NH4+-N concentration of the regeneration solution efficiently from 460 to 74.55 mg L-1 and the NH4+-N removal efficiency was 83.79%. Ammonium was recycled in the form of MAP finally.