Factors controlling the reversible and resistant adsorption and desorption of munitions constituents on soils.

摘要

The overall goal of this doctoral dissertation was to better understand the partitioning of a mixture of Munitions Constituents (MC) to soil by analyzing the effect of kinetics and reversible/resistant behavior of the MC. The product of the research were empirical models that can be used to determine future concentrations of MCs (1,3,5-Trinitroperhydro-1,3,5-triazine (RDX), Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6-Trinitrotoluene (TNT), Nitroglycerin (NG), Nitroguanidine (NQ), 2,4-Dinitrotoluene (DNT)) on the adsorption-desorption to soils of varying physical/chemical characteristics. The data was collected from batch experiments conducted near 1:1 (w/v) soil to solution ratios, which is more realistic because it reflects field conditions better than the dilute soil suspensions used in most studies. The adsorption was followed by multiple desorptions simulating rainy events to quantify the resistance of particular MC to desorption. Models were built by using the measured dissolved and particulate concentrations during the adsorption-desorption of MC, and the total organic carbon and other sorption phases present in the soils. Key soil properties were selected in order to use the minimal number of input parameters providing reasonable accuracy of predictions, but reflecting a wide range of soil characteristics to provide better application of the model in the field. Twenty-five soils from different places in America and Europe were used to isolate the effects of independent physical and chemical characteristics that affect sorption. One of the models analyzed in this research was the reversible/resistant model proposed by Di Toro and Horzempa [1]. The innovation was to apply it to the partitioning of mixtures of MC in different soil types taking into account the effect of kinetics and the electrolyte matrix in the adsorption and desorption steps. Results indicate that the model is sufficiently simple and flexible that can be used in the adsorption/desorption of the mixture of MC studied, because the fitting of the data was excellent even given the variation of time of equilibration and desorption and of the soil matrices. In addition to the reversible/resistant model, a multilinear sorption model was developed to predict partitioning of MC to soils by incorporating different sorption sites in addition to organic matter to improve the predictions. Clay minerals sites, CEC and extractable iron were included in the partitioning model. The clay sites were used in the multilinear model in two forms: the size particle fraction and charge sites content. To determine the charge sites, a method based on cesium sorption proposed by Anderson and Sposito [2] was refined and applied. This is the first time that this probe has been used for a wide range of soils with varying characteristics to develop a model incorporating specific sorption sites for the sorption of mixtures of MC. This method gave better fitting of the multilinear model than using size fractionation data of the clay, but the improvement was not enough to recommend its use due its cumbersome procedure.