Zeolite activation and ammonia-nitrogen removal from wastewater by adsorption on activated zeolite

The ammonia-nitrogen adsorption capacity of natural zeolite was evaluated after activation by salt,salt plus acid,salt plus alkali,heat,and heat activation followed by salt modification. The adsorption and desorption isotherms were examined. The activated zeolite was also used to adsorb ammonia-nitrogen from coal-coking wastewater pretreated by SBR-oxidation. The results show that the removal of NH+4-N by activated zeolite was the highest after activation in 0.3 mol·L-1 NaCl solution at 100℃. When the zeolite dosage was 10 g·L-1 and the contact time was 40 min,the NH+4-N removal rate reached 88.08%,40.73% higher than that (47.35%) of non-activated zeolite. The removal rate is dependent on zeolite dosage,wastewater pH and contact time. The adsorption isotherm curve of ammonia-nitrogen on salt-activated zeolite was well described by the Freundlich function. After the zeolite was regenerated by soaking in 1.5 mol·L-1 NaCl solution for 4 h,the efficiency of desorption of ammonia-nitrogen reached 89.30%. When 120 g·L-1 of the best modified zeolite was used to adsorb ammonia-nitrogen from coal coking wastewater pretreated by SBR-oxidation,the NH+4-N concentration dropped from 219.18 mg·L-1 to 4.8 mg·L-1,a removal rate of 97.81%. The adsorption isotherm of zeolite reaction with coking wastewater can be described by both the Freundlich and Langmuir functions.