Ammonium removal from high-strength aqueous solutions by Australian zeolite

Abstract

ABSTRACTRemoval of ammonium nitrogen (NH4+-N) particularly from sources which are highly rich in nitrogen is important for addressing environmental pollution. Zeolites, aluminosilicate minerals, are commonly used as commercial adsorbents and ion-exchange medium in number of commercial applications due to its high adsorption capacity of ammonium (NH4+). However, detailed investigations on NH4+ adsorption and ion exchange capacities of Australian natural zeolites are rare, particularly under higher NH4+ concentrations in the medium. Therefore, this study was conducted to determine NH4+ adsorption characteristics of Australian natural zeolites at high NH4+ concentrations with and without other chemical compounds in an aqueous solution. Results showed that initial NH4+ concentration, temperature, reaction time, and pH of the solution had significant effects on NH4+ adsorption capacity of zeolite. Increased retention time and temperature generally had a positive impact on adsorption. Freundlich model fitted well with adsorption process of Australian natural zeolites; however, Langmuir model had best fitted for the adsorption process of sodium (Na+) treated zeolites. NaCl treatment increased the NH4+ adsorption capacity of Australian zeolites by 25% at 1000 mg-N, NH4+ solution. The maximum adsorption capacity of both natural Australian zeolites and Na+ treated zeolites were estimated as 9.48 and 11.83 mg-N/g, respectively, which is lower than many zeolites from other sources. Compared to the NH4+ only medium, presence of other competitive ions and acetic acid in the medium (resembling composition in digested swine manure slurries) reduced NH4+ removal of natural and Na+ treated zeolites by 44% and 57%, respectively. This suggests detailed investigations are required to determine practically achievable NH4+ -N removal potential of zeolites for applications in complex mediums such as animal manure slurries.