A review of fly ash-based paste filling deamination methods

On the basis of discussing the status of fly ash-based paste filling technology, this paper further discusses the deterioration of downhole air environment caused by ammonia release in fly ash-based paste filling. By analyzing the mechanism of ammonia generation, it was found that NH₄ HSO₄ and (NH₄)₂SO₄ adsorbed in fly ash are soluble in water and generate NH₄⁺, which will be converted to NH₃ and released under alkaline environment. It is studied that the existing methods for removing ammonia adsorbed in fly ash solids, such as alkali addition, oxidation and heating methods, can remove ammonia to an appropriate range and meet the normal use of fly ash. However, since the alkali addition method and the oxidation method need to add chemicals and the fly ash after deamination treatment needs to be heated and dried, the heating method has higher requirements on the heat source, and the high cost makes these methods can not be widely used in the deamination treatment of fly ash-based paste filling. The fly ash is made into slurry, and the basic theory of physical and chemical deamination in sewage is used for reference, and the technical measures to remove ammonia in slurry by stripping method, break-point chlorination method and magnesium ammonium phosphate method are proposed. Among them, the stripping method is stable and does not require additional chemicals, while the break-point chlorination method and magnesium ammonium phosphate method can theoretically remove ammonia from slurry completely, but the required dosage is large, and it is difficult to control the dosage, which affects the ammonia removal effect and the performance of fly ash. Through a comprehensive comparison of the technical characteristics of the above deamination methods, combined with the economic evaluation that the stripping method for treating fly ash slurry has good prospects for engineering applications. Subsequent studies can optimize the operating conditions for the removal of ammonia from fly ash slurry by the stripping method through experiments or simulations, with a view to obtaining better deamination results. In addition, the performance of the filled paste formulated from the deaminated fly ash slurry needs to be paid continuous attention.