Performance and design of the availability test for measurement of potentially leachable amounts from waste materials

The availability test is used for measuring the potential leachability of components from solid, mainly inorganic residues and for distinguishing between leachable substances and those likely to be retained in the matrix. The objective of the presented study was to obtain results for discussion of the principles on which the availability test is based. Test conditions influencing the leaching process were identified. Experiments were based on the Dutch two-step pH static availability test (NEN 7341) and were performed in a two-level fractional factorial design on a municipal waste incineration bottom ash. The particle size, leachate to solid ratios (L/S), and time in the second leaching step (pH = 4) showed the largest impact on the leached amounts. A modification in comparison to existing and proposed protocols were recommended as follows: particle size of 95% less than 125 mu m, L/S ratio of 100 in each step, and leaching time of 18 h in the second step. A simplified model of the leaching by diffusion for each of the particle size distributions tested showed that more than 80% leaching of the available fraction by an efficient diffusion coefficient of pD(e) less or equal to 15 is possible to be obtained in the test.