Ammonium removal from high-strength aqueous solutions by Australian zeolite

ABSTRACT

Removal 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.

KEYWORDS:

• Ammonium adsorption
• adsorption isotherm
• nitrogen recovery
• waste treatment
• zeolite

Acknowledgments

Mr Gregory Stephen, CEO of Zeolite Australia Pty Limited is hugely appreciated for his assistance and support for this research. Mention of a specific product or vendor does not constitute a guarantee or warranty of the product by the authors and the institutions they are affiliated or imply its approval to the exclusion of other products that may be suitable.