Year of Award

2015

Document Type

Thesis

Degree Type

Master of Interdisciplinary Studies (MIS)

Degree Name

Interdisciplinary Studies

Other Degree Name/Area of Focus

Chemistry, Environmental Studies

Department or School/College

Interdisciplinary Studies Program

Committee Chair

Edward Rosenberg Ph.D.

Commitee Members

Vicki Watson, Aaron Thomas

Keywords

Uranium, Silica Polyamine Composite, Adsorption

Subject Categories

Chemistry | Environmental Chemistry | Environmental Health and Protection | Environmental Sciences

Abstract

Uranium is an element of interest because it is an abundant source of concentrated energy. In 1948 the US offered money for uranium ore mined in the US, which created a mining boom in the southwest that included the Navajo Reservation. During the late 1960s the demand for uranium decreased and many mining operations shutdown and left behind a legacy of contamination. As a result many Navajo communities have numerous water sources that exceed established maximum contamination levels for uranium and other toxic metals. These contaminations are a direct result of abandoned Cold War uranium mines and mill waste sites as well as the geology of the area. The improper disposal of these wastes has resulted in adverse health and ecological impacts.

Groundwater contaminations caused by heavy metal ions remain an environmental concern, despite many years of research on remediation. Traditional solvent extraction methods are expensive, time consuming and pose additional problems with the generation of waste products. The aim of this study is to use solid phase extraction methods to remediate contaminated water sources. An example is Silica Polyamine Composites (SPC), which have been used to filter, isolate and remove unwanted metals by acting as a chelating agent.

Given the high valent nature of uranium and the effectiveness of adsorption of metals from wastewaters and mine leachates by SPCs, we hypothesized that a phosphonated SPC will be effective at removing uranyl ions from contaminated water. An aminophosphonic acid functionalized SPC, BPAP, has been applied to uranium adsorption studies. This study has determined BPAP’s ability to be selective for uranium adsorption even in the presence of high concentrations of ions that form complexes with the uranyl cation, such as nitrate and sulfate, using batch capacity studies. Using ICP-OES analysis, we determined BPAPs capacity for uranium in aqueous solutions as 0.42 mmol/g. In addition, we have determined the working capacity of BPAP to be 146 mg/g under flow conditions. Although this result is far from ideal studies are currently underway to minimize the differences and acquire more accurate data. It is ideal to have both the batch capacity and working capacity to be close in value because it demonstrates the potential for a remedial application. One positive aspect of these studies are the recovery of the uranium from the BPAP column with a sodium carbonate gave a solution that was 50 times more concentrated than the feed. Again this shows the ability of SPCs, in general, to not only remediate but to also recover the metal(s) for the intent of reusability. Previous reports have shown that these materials can survive more than 3000 cycles of metal ion extraction, elution and regeneration with less than 10% loss of capacity.

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