Author

Hamid Hamid

Date of Award

Spring 2019

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

First Advisor

Joseph R.V. Flora

Abstract

The use of experimental studies with computer modeling is vital in the development of cost-effective methods for treating radium containing wastewaters. The goal of this dissertation is to develop a multi-scale model to study radium removal mechanisms onto silica and barite, and the effect of water quality parameters on radium removal. The major tasks to be accomplished in this study are: to develop a multi-component isotherm model for radium removal on different ionized silica surfaces; to re-parameterize sulphate force fields to account for metal-sulfate interactions; and to simulate radium removal on barite under different water quality conditions. We conducted molecular dynamics (MD) simulations to investigate radium removal on different ionized silica surfaces. The results indicate that high solution pH results in high radium removal due to increased silica surface negative charge, while high ionic strength results in less radium removal due to complexation and competition mechanisms with ions in the solution. The barite isotherm illustrate that ionic strength results in reduced radium removal due to complexation and competition mechanisms with the anions and cations in the solution but some inconsistencies were observed. The predicted isotherms for silica were consistent with experimental isotherm data. In order to accurately predict the removal of radium by adsorption onto the surface of barite, re-parameterization of the literature sulphate force fields were performed to account for metal-sulfate interactions. Different parameters were calculated using MD and umbrella sampling simulations to evaluate metal-sulfate interactions for different Me2+-SO4 systems. In general, the calculated parameters matched the experimental data, demonstrating that the re-parametrized force fields can accurately simulate the properties of barite and celestite, and will therefore could be effective for predicting the removal of radium by adsorption onto barite. The adsorption of different cations onto three barite surfaces (100, 010, and 001) were also simulated in the presence of different salts. The results show that radium removal decreases significantly with increasing ionic strength due to ions competitions and complexation mechanisms. In the case of CaCl2 and MgCl2 solutions, the isotherm predictions based on the multi-component Langmuir isotherm followed the expected trend while the trend for BaCl2, SrCl2, and NaCl solutions were not consistent with experimental isotherms. The findings in this study can elucidate radium removal mechanisms under different conditions to assist in the development of effective treatment technologies.

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