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Modeling the leaching behavior of fly ash solidified/stabilized wastes.

机译：模拟粉煤灰固化/稳定化废物的浸出行为。

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Pollution of groundwater may be caused by disposal of hazardous wastes on land. One method that has been found adequate for the disposal of wastes is the solidification/stabilization process. The solidified form is obtained by combining a pozzolanic material, such as fly ash, with the waste.; In order to establish the environmental acceptability of the solidified/stabilized waste for land disposal, the U.S. Environmental Protection Agency has developed the toxicity characteristic leaching procedure (TCLP) test. The test simulates the behavior of the waste under non-equilibrium conditions by contacting the waste with an acidic media and by measuring the concentration of material leached from the waste after 18 hours of continuous agitation.; The first purpose of the present research is to develop a mathematical model to explain the leaching behavior of heavy metals contained in fly ash solidified/stabilized wastes. The model would help in understanding the leaching behavior and preventing the leaching of heavy metals under the “worst case” leaching conditions established by the toxicity characteristic leaching procedure. In the model it is assumed that once the waste is contacted with the leaching solution, the heavy metals diffuse and then reprecipitate as hydroxide. To develop the model, a combination of Fick's diffusion theory and theoretical equations for the solubility of chromium, cadmium, and aluminum is used. The TCLP test is run in a semi-batch mode during 100 hours to simulate real environmental conditions. It was found that only cadmium behaves under the assumption given by the model, having the species Cd(OH)+1 as the limiting solubility species.; The other purpose of this research is to develop a statistical model to quantify the amount of heavy metals released from the solidified/stabilized waste to the leaching solution. The model would allow selecting the most appropriate process conditions in the formation of the solidified waste and to minimize the release of the metals. The model is based on a simplex-centroid and a 26-3 fractional factorial experimental designs. A linear polynomial equation was found to quantify the amount of chromium and cadmium release, whereas a third degree polynomial was required for the same purpose for aluminum.
机译：处置土地上的危险废物可能导致地下水污染。已发现适合处理废物的一种方法是固化/稳定化过程。固化形式是通过将火山灰材料（例如粉煤灰）与废物混合而获得的。为了确定固化/稳定化废物用于土地处置的环境可接受性，美国环境保护署开发了毒性特征浸出程序（TCLP）测试。该试验通过使废物与酸性介质接触并测量连续搅拌18小时后从废物中浸出的物质的浓度，来模拟废物在非平衡条件下的行为。本研究的第一个目的是建立一个数学模型来解释粉煤灰固化/稳定化废物中所含重金属的浸出行为。该模型将有助于了解在通过毒性特征浸出程序建立的“最坏情况”浸出条件下的重金属浸出行为，并防止重金属浸出。在该模型中，假设废物与浸出溶液接触后，重金属就会扩散，然后以氢氧化物的形式再沉淀。为了开发模型，结合了Fick扩散理论和铬，镉和铝的溶解度的理论方程式。 TCLP测试以半批量模式运行100小时，以模拟实际环境条件。结果发现，只有镉在模型给出的假设下表现出来，以Cd（OH） +1 为极限溶解度。这项研究的另一个目的是开发一种统计模型，以量化从固化/稳定化的废物释放到浸出溶液中的重金属量。该模型将允许在固化废物的形成中选择最合适的工艺条件，并最大程度地减少金属的释放。该模型基于单纯形质心和2 6-3 分数阶乘实验设计。发现线性多项式方程可量化铬和镉的释放量，而出于铝的相同目的，需要三次多项式。

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