Serial batch leaching procedure for characterization of coal fly ash

Abstract

Although many leaching methods have been used for various purposes by research groups, industries, and regulators, there is still a need for a simple but comprehensive approach to leaching coal utilization by-products and other granular materials in order to estimate potential release of heavy metals when these materials are exposed to natural fluids. A serial batch characterization method has been developed at the National Energy Technology Laboratory that can be completed in 2-3 days to serve as a screening tool. The procedure provides an estimate of cumulative metals release under varying pH conditions, and leaching the sample at increasing liquid/solid ratios can indicate the rate at which this process will occur. This method was applied to eight fly ashes, adapted to the acidic or alkaline nature of the ash. The leachates were analyzed for 30 elements. The test was run in quadruplicate, and the relative standard deviation (RSD) was used as a measure of method reproducibility. RSD values are between 0.02 and 0.70, with the majority of the RSD values less than 0.3. The serial batch leaching procedure was developed as a simple, relatively quick, yet comprehensive method of estimating the risk of heavy metal release from fly ash when it is exposed to natural fluids, such as acid rain or groundwater. Tests on a random selection of coal fly ashes have shown it to be a reasonably precise method for estimating the availability and long-term release of cations from fly ash.

Mobility of trace elements in fly ash and in zeolitised coal fly ash

“…In accordance with Hesbach et al [9], each pH step cannot be considered as an individual event. Leachate composition after a step will depend on both this pH environment and on interactions solid-leaching solution occurred during the previous leaching steps.…”

“…The values are reported in Table 2. Leaching tests were performed using sequential batch tests based on the approach used by Hesbach et al [9]. The individual leaching step volumes and their run times were indicated in Table 1.…”

“…The procedure provides a determination of the metals released under varying pH conditions starting from a solution with pH value comparable to that of the fly ash samples (alkaline pH). The first step was to determine the pH of fly ash and zeolitic fly ash samples [9]. The samples were then leached at progressively more acidic pH values.…”

“…Although coal fly ash is partly used in concrete and cement manufacturing, more than half percent of the production is disposed of in landfills. A method to evaluate the elemental mobility in coal fly ash is to perform leaching tests using different leachant solutions [2][3][4][5][6][7][8][9][10][11]. The crucial factors in element solubility are the leaching time, the solubility kinetics, the liquid/ solid ratio (L/S) and the influence of the leachant pH.…”

Combustion and Leaching Behavior of Trace Elements in Lignite and Combustion by-Products From the Muğla Basin, Sw Turkey

“…There are two major types of leaching tests concerning their set up: Column tests, which better simulate field conditions, and batch tests, which provide evidence for the maximum potential mobility of an element. Batch tests are more widely applied due to their relatively rapid and reliable results but can easily misinterpreted if only absolute values are to be considered (Siavalas et al, 2007;Baba et al, 2008;Hesbach et al, 2009). The lignite mining activities in Turkey appear to have serious repercussions in underground waters.…”