Column leaching experiments

Melancon, S.M., J.E. Pollard, and S.C. Hern (1986). Evaluation of SESOIL, PRZM, and PESTAN in a laboratory column leaching experiment. Environ. Toxicol. Chem., 5 865-878. 

Results of batch leach experiments on tailings samples have shown that As, Se, Mo, Cr, and V, stable as neutral ion pairs, ions, and oxyanions, are enriched in the silt and claysized fraction. This enrichment may contribute to a contaminant source lasting for several decades. From column leach experiments, the concentrations and mobilities of several species and elements follow the order S0 >NH >N02>Al>Mn>U>Fe>Se > PO > Ni > As > Cd at pH 4.0. 

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

In most column-leaching studies, the bulk of triazines remain near the soil surface. For instance, Kruger et al. (1993) found that in a 60-cm column of Iowa soil taken from a held with no previous pesticide history, approximately 1.2% of the 14C-atrazine was recovered in leachate over a 12-week period. By the end of the experiment, 77% of the 14C applied remained in the upper 10 cm of soil, and bound residue was the primary component. Both atrazine and degradation products (DIA > HA > DEA > DEHA > DIHA) were found in the top 10 cm of surface soil. 

FIGURE 12.2 A schematic of the sequential leaching experiment through 5-cm soil columns from the E, Bs, and BC horizons (FF = forest floor). 

L. (2000). Column leaching and sorption experiments to assess the mobility of potentially toxic elements in industrially contaminated land. J. Environ. Monit. 2, 234-239. 

Leaching Experiment. Three polyethylene columns (4.8 cm ID by 50 cm height) ware employed to investigate the mobility of dicamba, 2,4-D, atrazine, diazinon, pentachlorophenol, and lindane. Each column was packed with 1,080g of fresh soil to a depth of 40 cm (sandy loam soil from Soils Incorporated, Puyallup, Washington pH 5.9 to 6.0 89 percent sand 7 percent silt 4 percent clay cation exchange capacity 7.5 meq/lOOg). 

In Chapter 3.4 a method has been presented for long-term prognosis of metal pollutant mobility, which combines column circulation leaching experiments at variable pH/E -conditions with sequential extraction procedures on the solid waste material before and after these experiments (Schoer FSrstner, 1987). Temporal release patterns are different for the individual elements (Figure 6-5) While at pH 5/400 mV release of cadmium seems to be completed within the experimental period mobilization of copper is still going on and the end point cannot be estimated from the data of the "kinetic" experiments. The same effect has been found for the examples of thallium and vanadium. For the other elements, the endpoint of release can be determined as approximately 10 mg cobalt, 0.6 mg cadmium, 600 mg zinc and 0.3 mg chromium, 2 mg barium and 20 mg lead (per 100 g of solid substrate treated with 140 L solu-... 

Fig. 6. Comparison of laboratory column leaching data and results from large scale lysimeter experiments.

These authors observed that the leach solutions of chalcocite become more and more depleted in Cu and that this depletion is accompanied by a decrease of the Cu/S ratios of the solution from 2 to 1, which these authors ascribe to fractionation between diversely coordinated Cu in the different minerals. In contrast to chalcocite, chalcopyrite leaching produces no isotope fractionation. These authors also conclude from a comparison between columns seeded with bacteria and sterile columns that bacterial mediation had little if any influence on Cu isotopic fractionation in this specific experiment, which simply reflects that bacteria do not store signiflcant amounts of metal. 

The failure to observe any leaching could either indicate that the initial dissociation of the supported phosphine-rhodium(I) bond does not occur or that having been displaced from one site within the support the rhodium subsequently binds to another site. This latter possibility would not lead to any significant leaching in experiments where the catalyst was shaken with the reactants, although, if the reactants were passed through a bed or column of catalyst, leaching should then be observable. 

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