Pretreatment method for the utilization of the coal ash landfilled in ash ponds

Abstract

The coal ash (CA) generated from coal-fired power plants (CPPs) is collected in ash ponds (APs), most of which are actually full, so there are concerns regarding the potential contamination of the environment around them. Thus, in the present study, a method for improving the utilization of coal pond ash (CPA) was proposed. Here the CA landfilled in an AP was regarded as CPA. Furthermore, the CPA characteristics (particle size and weight distributions, chemical composition, unburned carbon (UC) content, particle image, and mineralogical analysis) were investigated. Next, experiments were conducted on the main separation processes: screening with five standard sieves having 0.15-, 0.3-, 0.6-, 1.18-, and 2.36-mm diameter grids; float–sink experiments with four different specific gravities (SGs) of under 1.8 SG, 1.8–2.2 SG, and 2.2–2.5 SG and over 2.5 SG; flotation with a column-type glass reactor under the conditions of pH 2, 7, and 12; grinding with a batch-type ball mill for 5, 10, 20, and 40 min; wet magnetic separation with four magnetic forces (0.1, 0.5, 1, and 2 T). Based on these results, a pretreatment method was proposed and the final materials could be categorized into UC, amorphous compounds (ACs) with Al species (Al2O3∙xH2O) and glassy phases, inorganic materials with Si and Al, and ferrous material groups. Besides, six additional pretreatment methods were suggested through various combinations of each separation process. As a case of South Korea, the applicability of this method to the entire CPA in South Korea was also confirmed.