ECN publication
The influence of particle size on leaching of elements from coarse granular materials
Published by: Publication date:
ECN 1998
ECN report number: Document type:
ECN-C--98-045 ECN publication
Number of pages: Full text:
62 Download PDF  

In the framework of CEN standardization a compliance test for granularmaterials has been formulated, which is divided in four parts covering different test conditions. The recently added fourth procedure had a particle size range up to 40 mm. Concern was expressed about the repeatability of this latter procedure. This prompted an investigation of the effect of different particle size ranges on the leaching result. The materials studied are MSWI bottom ash, phosphate slag and crushed cement-stabilized MSWI fly ash. The particle size ranges studied ranged from 0 - 0.2 mm up to 40 mm. The results of the study show that the relative standard deviation increases on average for the three materials from the 0-4 mm, 0-10 mm to the 0-40 mm size fraction. The frequently voiced notion that upon size reduction leaching increase has been proven wrong as a general statement. Several elements show the opposite behaviour: higher leachability from coarser material than from fine material. This phenomenon is often associated with a change in pH between coarse and finer size fractions (the coarser being lower in pH). Phosphate slag shows the most significant particle size effect, which can be explained by the dense internal structure of slag, which enhances the particle surface effect. Still the most significant difference does not amount to more than a factor of 6 between the size fractions 0-4 mm and 0-40 mm. For more porous materials such as MSWI bottom ash, the effect is much smaller, however with a much higher relative standard deviation for the 0-40 relative to the 0-4 mm fraction. The 0-40 mm size range in the fourth test is strongly discouraged to enhance robustness and repeatability of the test. Based on practicality and repeatability, the best size range for the compliance leach test is 0-4 mm, where the sensitivity to the particle size distribution is less critical. 4 refs.

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