Hydrothermal synthesis of zeolitic material from circulating fluidized bed combustion fly ash for the highly efficient removal of lead from aqueous solution

The utilization of coal fly ash derived from circulating fluidized bed combustion(CFBFA)still faces great challenges because of its unique characteristics.In this study,a zeolitic material with Na-P1 zeolite as the main phase was successfully synthesized via a hydrothermal method by using CFBFA as the raw material.The effects of hydrothermal temperature,time,and added CTAB amount on the characterizations of synthesized materials were investigated by XRD,SEM,and XPS.The properties of the optimal zeolitic material and its adsorption performance for Pb^(2+)in aqueous solution were evaluated.The influences of pH,initial concentration,dosage,and temperature on Pb^(2+)adsorption were also examined.Results revealed the following optimal parameters for the synthesis of zeolitic material:NaOH concentration of 2 mol·L^(-1),solid-to-liquid ratio of 1:10 g·ml^(-1),hydrothermal temperature of 110℃,hydrothermal time of 9 h,and CTAB amount of 1 g(per 100 ml solution).The adsorption capacities of the zeolitic material reached 329.67,424.69,and 542.22 mg·g^(-1) when the pH values of aqueous solution were 5,6,and 7,respectively.The Pb^(2+)removal efficiency can reach more than 99%in aqueous solution with the initial concentrations of 100-300 mg·L^(-1) under pH 6 and suitable adsorbent dosage.The adsorption and kinetics of Pb^(2+)on the zeolitic material can be described by Langmuir isotherm and pseudo-second-order kinetic models,respectively.The ion exchange between Pb^(2+)and Na^(+)and chemisorption are the main adsorption mechanism.All these findings imply that the synthesis of low-cost adsorbent for Pb^(2+)removal from weak acid and neutral aqueous solution provides a highly effective method to utilize CFBFA.

Preheating Characteristics of Datong Coal in O2/CO2 and Air Atmospheres

Experimental studies were carried out to find the difference of preheating characteristics of Datong coal in O_2/CO_2 and air atmospheres by a circulating fluidized bed. It is found that pulverized coal could be both steadily preheated to above 800°C in the two different atmospheres, but the temperature distribution was more uniform along the riser in O_2/CO_2 atmosphere. During the preheating, the content of CO in the flue gas can reach 12.32% under the O_2/CO_2 atmosphere, far higher than that in air(5.94%). Simultaneously, the conversion rate of fixed carbon was higher in O_2/CO_2 atmosphere compared with that in air. It can be inferred the higher oxygen concentration and higher partial pressure of CO_2 have greatly accelerated the gasification reaction. The BET analysis indicated a number of large pores were transformed into micropores during the preheating progress, and the major contributors for overall pore volume of chars and specific surface area are the micro-pores and the mesopores with diameter ranging from 2 nm to 10 nm. The inner pore structure was more developed in O_2/CO_2 atmosphere.