Preparation of non-sintered fly ash filter (NSFF) for ammonia nitrogen adsorption

ABSTRACT

In accordance with China’s goal of ‘treating wastes with wastes, turning wastes into treasure’, a non-sintered fly ash filter (NSFF) with sewage sludge as additive was prepared. It consists of 70.9% fly ash, 7% sewage sludge, 9% cement, 7.1% CaO, 1% NaHCO₃ and 5% sodium silicate solution. After mixing, 34 g/(100 g dry material) water was added, and then was granulated and steam cured under 80°C for 16 h. NSFF’s main performance indexes include specific surface area (SSA) of 17.038 m² g⁻¹, filter media breaking rate (FMBR) of 2.2%, apparent density (AD) of 1140 kg m⁻³, and porosity of 41.67%, meeting the Chinese Standard CJ/T 299-2008. This NSFF has a larger SSA and a lower AD comparing with the other similar non-sintered fly ash ceramsite products. Moreover, leaching toxicity of the NSFF has met the Chinese Standards for Hazardous Wastes (GB5085.3-2007). Therefore, the NSFF is effective and safe to use as a water treatment filter media. The NSFF’s adsorption characteristics for ammonia nitrogen was investigated. Results showed that the optimized parameters for ammonia nitrogen adsorption are as follows, NSFF dosage at 5 g, initial ammonia nitrogen concentration of 225 mg L⁻¹, pH at 7, contact time of 12 h and temperature at 30°C. Under the optimum conditions, the adsorption capacity of NSFF for ammonia nitrogen was 4.25 mg g⁻¹. The adsorption process can be best described by Langmuir isotherm and pseudo-second-order kinetic model. The proposed adsorption mechanism include adsorption and cation exchange.

KEYWORDS:

• Ammonia nitrogen
• sewage sludge
• non-sintered fly ash filter
• adsorption
• waste reuse

Acknowledgements

This work was supported by the National Twelfth Five-Year Plan for Science & Technology Pillar Program under Grant [2012BAJ21B06]. The authors also thank the anonymous reviewers for their invaluable insight and helpful suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by National Twelfth Five-Year Plan for Science & Technology Pillar Program [grant number 2012BAJ21B06].