Final Report: Thioether Amended Silica-Polyamine Composite Materials for Mercury (II) Extraction

EPA Contract Number: 68D00260
Title: Thioether Amended Silica-Polyamine Composite Materials for Mercury (II) Extraction
Investigators: Ficher, Robert J.
Small Business: Purity Systems Inc.
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: September 1, 2000 through March 1, 2001
Project Amount: $69,368
RFA: Small Business Innovation Research (SBIR) - Phase I (2000) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , SBIR - Water and Wastewater , Small Business Innovation Research (SBIR)

Description:

This Small Business Innovation Research Phase I project was undertaken to develop a silica-polyamine composite material to be used in an efficient, environmentally benign system to extract oxidized mercury from coal-fire flue gas desulfurization water to levels less than 2 ppb.

Presently over 200 of the largest coal-fired utility boilers in the U.S. utilize flue gas desulfurization (FGD or wet scrubbers) process. While these processes were designed primarily to remove sulfur dioxide from the plant emissions, these wet scrubbers also entrain oxidized mercury in the scrubber water. Literature reports indicate that the mercury levels in the scrubber water can reach levels of 600 ppb. The primary treatment strategy for the water is precipitation in large settling ponds. These ponds can be an attractive hazard to local wildlife with their high levels of mercury contamination and require large tracts of land on which to be built.

Initially nine different silica-polyamine thioether composite materials were synthesized. One of these, PAA-een was chosen to carry out the bulk of testing on due to ease of synthesis and price of the required reagents. These are two areas that greatly influence the final price of the material and therefore it's competitive ability.

This material was tested in both high and low mercury concentration batch tests and flow tests carried out on both a "clean" mercury contaminated solution and on scrubber water that was "spiked" to yield a 100 ppb scrubber water. Tests were also carried out to determine the most effective way to strip the material of the mercury and prepare it for another extraction cycle.

Summary/Accomplishments (Outputs/Outcomes):

When challenged with high mercury concentration solutions all of the silica-polyamine materials exhibited high capacities for Hg++. Batch capacities ranged from 1.03 mmol Hg++/g of extractant to 1.42 mmol Hg++/g of extractant. Flow capacities ranged from 0.45 mmol Hg++/g of extractant to 0.98 mmol Hg++/g of extractant. These numbers indicate that the materials can extract a large amount of mercury (II) from high concentration solutions but do not reveal the effectiveness of the material at removing mercury to low ppb levels. We have demonstrated the materials ability to reduce relatively high (100 ppb) concentrations of mercury to below discharge levels (2 ppb) when slow flows are used (Figure 1).

We have shown that these materials are effective at reducing low (10 ppb) concentrations of mercury to below discharge levels (2 ppb) as well as higher concentrations to below these limits. This indicates that these materials will be useful in applications where low volumes of mercury (II) contaminated solutions need to be treated and a low mercury (II) concentration in the treated water is important. Applications include Mercury contaminated remediation sites as well as coal-fired power generators.

Conclusions:

The outcome of this project is the creation of a material that is highly effective at reducing mercury concentrations from relatively concentrated aqueous solutions. The process has been demonstrated to reduce the mercury concentration from 100 ppb to less than 2 ppb at treatment rates of 10 column volumes / hr. Approximately 55 g of material was used to treat 15,500 g of water containing 100 ppb of mercury to below 2 ppb. While it was shown that the material could be stripped using HNO3 this experiment needs to be reproduced and the material needs to be tested to determine its ability to continue extracting mercury to low levels.
This material may be suitable for high volume treatment applications such as scrubber water treatment with the appropriate stripping protocol; it also seems particularly suited for use in remediation applications such as National energy laboratory clean-ups and other sites with high levels of mercury contamination.

Supplemental Keywords:

soft metal extraction., RFA, Scientific Discipline, Toxics, Waste, Water, Chemical Engineering, Wastewater, Environmental Chemistry, Chemistry, HAPS, Hazardous Waste, Chemistry and Materials Science, Engineering, Hazardous, 33/50, Environmental Engineering, Mercury, hazardous waste treatment, wastewater treatment, silica-polyamine composite, industrial wastewater, silica materials, mercury (II) extraction, mercury & mercury compounds, Mercury Compounds