Ultrasonic strengthening characteristics of ammonia release during the preparation of fly ash based filling paste

Abstract

Fly ash-based paste-filling mining can not only effectively control land subsidence and increase the coal recovery rate, but it also solves the problem of fly ash accumulation in coal-fired power plants. The release of ammonia from fly ash-based filling paste contaminates the air environment of the coal mine filling face, necessitating immediate remediation. This study proposes a new method of using ultrasound to promote the release of paste ammonia. Through the ultrasonic treatment of fly ash slurry, the ultrasonic time (A), ultrasonic power (B) and solid-liquid ratio (C) are used as investigation factors. The results show that the ammonia release rate increases first and then decreases with the increase of ultrasonic time, ultrasonic power and solid-liquid ratio, and reaches the maximum when the ultrasonic time, ultrasonic power and solid-liquid ratio are 30 min, 80 W and 1∶10, respectively. The response surface experiment is conducted on the basis of single factor test to establish a regression model. The optimal experimental parameters are determined by response surface optimization. The results show that the order of influencing factors is: A > B > C, AB > AC > BC. The optimum experimental parameters for ammonia removal are as follows: ultrasonic time is 32 min, ultrasonic power is 80 W, and solid-liquid ratio is 1∶7.7. Through verification, it is found that there is only a relative error of −1.6% between the measured value and the predicted value. The optimized experimental parameters are used to treat the fly ash to prepare the filling paste to determine the ammonia release amount. It is found that the ammonia release amount of the paste is reduced by 95.94%. The ammonia release rate increases by 84.02%, and the uniaxial compressive strength of the paste at 3 d and 28 d increases by 185.00% and 86.50%, respectively. The slump, bleeding rate and setting time are decreased, and the number of harmful pores in the paste is reduced, so that the porosity is decreased from 33.58% to 28.13%. It provides a new method for the ammonia release treatment of the fly ash-based filling paste.

Keywords

• ammonia release
• ultrasound
• filling paste
• fly ash
• response surface methodology