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, 34â g/(100â g dry material) water was added, and then was granulated and steam cured under 80°C for 16â h. NSFF's main performance indexes include specific surface area (SSA) of 17.038â m2â g-1, filter media breaking rate (FMBR) of 2.2%, apparent density (AD) of 1140â kgâ 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 5â g, initial ammonia nitrogen concentration of 225â mgâ L-1, pH at 7, contact time of 12â h and temperature at 30°C. Under the optimum conditions, the adsorption capacity of NSFF for ammonia nitrogen was 4.25â mgâ 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.
Subject(s)
Ammonia , Coal Ash , Adsorption , China , NitrogenABSTRACT
A series of Li4SiO4 was synthesized using LiNO3 and six different silicon precursors. The precipitated-silica-derived Li4SiO4 presented the highest CO2 capacity in a 10 h sorption test, and ZSM-5-derived Li4SiO4 demonstrated the most rapid CO2 sorption. The CO2 sorption kinetics predominantly followed the nucleation mode and could be accurately described by the Avrami-Erofeev model. The Avrami-Erofeev model provided an in-depth analysis of correlation between sorption performance and material properties. Both the nucleation speed and nucleation dimensionality affected the overall sorption kinetics. The kinetics and pore-size distribution suggest that the sorption kinetics was dependent on the quantity of â¼4 nm-pores which favors nucleation dimensionality. For the cyclic tests, the precipitated-silica-derived sample presented the poorest performance with the capacity decreasing from 31.33 wt% at the 1st cycle to only 11.52 wt% at the 30th cycle. However, the sample made from fumed silica displayed an opposite trend with the capacity increasing from 19.90 wt% at the 1st cycle to 34.23 wt% at the 30th cycle. The radically distinct behaviour of samples during cycles was on account of the alternation of sorption kinetics. The decrease in â¼4 nm-pores after cycles was responsible for the decrease of nucleation dimensionality for the precipitated-silica-derived sample. The rearrangement during cycles could enrich the pores of â¼4 nm for the fumed silica-derived sample, which improved the nucleation growth, thus enhancing the kinetics with cycles.