Column leaching test

Generally, there is no simple and easy theoretical procedure which can provide exact or nearly precise quantitative predictions of what and how much will be adsorbed/desorbed by any solid phase over a period of time [9, 136-139]. Understanding sorption/desorption characteristics of any solid phase materials requires two main laboratory experimental techniques (a) batch equilibrium testing, and (b) continuous solid phase column-leaching testing. These involve... 

Whereas batch equilibrium tests are designed to study equilibrium sorption of solid phase particles with various pollutants, singly or in combination with other pollutants, solid phase column-leaching tests study both sorption and diffusion of organic pollutants through the subsurface environment [10,11,127, 141,142]. 

Fig. 2. Schematic diagram of the continuous column-leaching test experiment...

It is important to differentiate between the two different types of sorption/ desorption tests (i. e.,batch and column-leaching), and the sorption characteristics determined from one should not be confused with the other. Sorption isotherms obtained with batch equilibrium tests are applied mainly to solid suspensions. The physical model, assumed with this situation, is one of a completely dispersed solid particle system, where all solid particle surfaces are exposed and available for interactions with the contaminants of concern. In contrast, column-leaching tests are performed with intact solid samples, and the sorption characteristics obtained from them are the results of contaminant interactions with a structured system where not all-solid particle surfaces are exposed or available for interactions with the contaminants. 

Fig. 1. Variations in elemental concentrations in fresh Drax, weathered Drax and weathered Meaford fly ash eluates treated with deionized water in column leaching tests (DF Drax fresh, DW Drax weathered, MW Meaford weathered).

Batch leaching tests are generally taken as an initial step to evaluate toxicity of the ashes because the batch tests represent the best leaching conditions and generate the highest quantity of leachates (Benito et al. 2001). Serial batch leaching tests also often successfully simulate ash pond conditions (Praharaj et al. 2002), whereas the column leaching tests simulate dry ash disposal (Benito et al. 2001). 

Simulation leaching tests are upward-flow (NEN, 7343, 1995) and downward-flow column leaching tests (Huang et al., 2003). Laboratory leachates are collected on a regular basis, chemically monitored and tested with (at least) two aquatic bioassays (see below). 

This paper evaluates the effect of the fixed waste s alkalinity on the release patterns of heavy metals from the solidified waste. Both batch and upflow column leaching tests were used to study this effect. The results of this research indicate that the leaching rate of heavy metals from stabilized/solidified wastes is governed by the amount of alkalinity present in the waste. Appreciable metal leaching will not occur untQ enough of the buffering capacity of the waste has been neutralized so that the pH of the leachant drops to 6.0 or less. Consequently, the U.S. EPA test, which limits the amount of leachant acid used, is not valid for the evaluation of these types of waste. 

Column leaching tests were performed in the upflow mode. The columns were Buchner type funnels that were modified by a glassblower. The modifications included addition of a side rm for effluent flow and tapering the neck of the funnel to a pipete-like tip to accomodate narrow bore tubing. 

T. M. Brown, Column Leach Testing of Heavy Metal Sludges Stabilized/Solidified with Portland Cement An Investigation of Release Meehanisms, M. S. Thesis, Univ. of New Hampshire, Durham, NH (1984). 

Table VI. Results of Column Leach Tests on Tailings Samples, Maybell, Colorado (all concentrations in mg/L unless noted)...

Kim SY, Tanaka N, Matsuto T, Tojo Y. (2005). Leaching behavior of elements and evaluation of pre-treatment methods for municipal sohd waste incinerator residues in column leaching tests. Waste Management Research 23(3) 220-229. 

In column leaching tests with sediment collected from the banks of the Rhone River, the presence of dissolved organic matter and pH was found to be the factors controlling the adsorption and mobility of zinc (Bourg and Darmendrail 1992). 

Column leaching tests are designed to determine the rates of desorption under conditions of low mixing, high surface areas, and continuous surface renewal. The flat plate tests are designed to determine desorption under conditions of low mixing, low surface areas, and diffusion-Umited surface transport. Table 22 summarizes information about each test... 

F. Castro and G. Pereira Characterization of the Nickel Laterite Sample and Guidelines for Column Leach Tests Project AMIRA P986, (Vale Mineral Development Center, Brazil, 2009). 

Garlanger, J. E., and Ingra, T. S., 1983A, Evaluation of Engineering Properties and Wet Stacking Disposal of Widows Creek FGD Gypsum-Flyash Waste, Addendum 1 EP Toxicity and Column Leaching Tests, TVA/OP/EDT-84/23, December. 

Serial batch leaching and column leaching tests... 

During long-term leaching in field situations, phases that initially buffer the pH/ A of the leachate can become exhausted with important consequences for the release rate of contaminants. For example, Baverman et al. (1997) showed that copper release from sulphidic mine waste became much more rapid after exhaustion of a pH-buffering calcite phase. In order to investigate such behaviours, serial batch tests and column leaching tests have been devised. 

Column leach test (NEN 7343, 1995) and draft percolation simulation test... 

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