Method 1315 – Mass Transfer Rates
Mass Transport Rates of Constituents in Monolithic or Compacted Granular Materials Using a Semi-dynamic Tank Leaching Procedure
Summary:
This test provides mass transfer release rates of constituents through low permeability material under diffusion-controlled release conditions. The method consists of tank leaching of monolithic or compacted granular material with periodic renewal of the leaching solution. Monolithic samples may be cylinders or parallelepipeds while granular materials are compacted using modified Proctor compaction into cylindrical molds at optimum moisture content. Samples are transferred to fresh reagent water at nine pre-determined intervals and eluate concentrations are plotted as a function of time. Mass transport parameters (e.g., observed diffusivity) may be estimated through analysis of mean interval flux and cumulative release data.
Detailed Description:
Method 1315 is used to determine mass-transfer based release rate information from either monolithic or compacted granular materials in a sequential tank test. Mass transport is the dominant release mechanism when water flows around a material with low hydraulic conductivity relative to surrounding materials.
Test specimens may be monolithic material (e.g., cement-based waste, concretes, glass, bricks) formed, cut or molded into cylinders or blocks or granular materials (e.g., sediments, soils, ash) compacted using Proctor compaction effort into cylindrical molds. Tank dimensions must be related to the size of the specimen and allow for a specfied liquid-to-surface area ratio (L/A) of 9 mL/cm2.
The specimen is sequentially suspended in a series of nine tanks of leaching solution for pre-determined leaching intervals. The leaching solution is typically deionized water, but other solutions are possible. The specimen undergoes continuous leaching and is transfered from tank to tank at the end of each leaching interval. The eluates from each leaching interval are analyzed for pH, conductivity, oxidation-reduction potential (optional), and concentrations of constituents of potential concern (COPCs).
Eluate concentrations, mean interval mass flux, and cumulative release are plotted as a function of leaching time and used to determine mass transfer properties (e.g., diffusivity).
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Overview Presentation of Method 1315