Deloro Mine Arsenic Remediation Technologies

Deloro Mine

Arsenic Remediation Technologies

The purpose of this research is to determine if new methods now exist that may further help to reduce post-treatment effluent to a level that would not be considered hazardous to humans. This literature review will focus on exploring new technologies that may help to reduce effluent levels that are currently being introduced into the Moira River. This literature review will explore new technologies that may be applicable to the reduction of arsenic at the Deloro Mine site.

Arsenic remediation technologies are divided into nine process categories. Often remediation combines two or more of these technologies to achieve the final result. The nine treatment processes are: oxidation, coagulation/co-precipitation, sedimentation, filtration, adsorption, ion exchange, membrane/reverse osmosis, biological and other site-specific applications that do not fall into any of the other categories (MIT, 2001). The types and combinations of techniques used depend on site-specific conditions and the arseno-compounds present.

Commonly Used Remediation Techiniques

Oxidation. The most common forms of arsenic are arsenate and arsenite. Treatment processes are most effective in the removal of arsenate. However, arsenite is problematic because it is typically non-charged below a pH of 9.2. Oxidation is used as a step in many treatment plans to convert arsenite to arsenate, which can then be removed by other processes (MIT, 2001).

Coagulation/Co-Precipitation. Coagulation refers to mechanisms that result in particle enlargement (floc formation). In this process, particles are grown to a size where they will settle out (MIT, 2001). This precipitate is easily removed by physical means. There are four types of co-precipitation: inclusion, adsorption, occlusion, and solid-solution formation (MIT, 2001). This type of remediation is typically used if particles are small. At the Deloro site, particles are already large and bound as arsenopyrite. Filtration may be the preferred method, depending on the results of the analysis.

Physical Removal Processes. The purpose of coagulation is to render soluble arsenic into a form that can be separated by physical removal methods by physical means such as sedimentation, filtration, and adsorption (MIT, 2001). The success of these methods depends on the ability to coagulate arsenic into a form that is a large particulate.

Chemical Processes. Several chemical processes have been recently developed in areas where a large-scale decontamination must be accomplished. Ion exchange is a reversible exchange of ions between the solid and liquid phase of the materials. However, there is no permanent change in the structure of the solid. This process is currently being employed on a village scale in Bangladesh (Clifford, 1999).

Biological Treatment. This process removes arsenic by means of microorganisms. In this process, bacteria accomplish removal by oxidation, reduction, mineralization, detoxification, or methylation. It is typically used for smaller remediation projects, not those of the size and scale of the Deloro Mine.

Other remediation techniques are available for remote rural areas, such as dug well, deep tube wells, ponds, and solar distillation of arsenic (Johnston & Heijnen, 2001). These are only suitable for extremely small contamination areas, or where the levels are considerably low. They would not be suitable for a site the size of the Deloro Mine, therefore will not be discussed at length. Many of the more common technologies for removing arsenic are almost 80 years old. However, there are some new technologies being developed that may help to alleviate the problems and limitations associated with standard removal techniques.

Review of New and Innovative Technologies

As one can see, there are a number of treatment options available for the removal of arsenic in groundwater. There is no single best solution that will result in maximum results at all sites. These technologies are often combined to meet the needs of each individual situation. Treatment at the Deloro Mine uses chemical coagulation followed by sedimentation to process the effluent that will eventually be dumped back into the Moira River.

The newest innovation in arsenic treatment was announced February 8, 2008 by AdEdge Technologies. This company has released a specialty adsorbent filtration system specifically designed to remove arsenic from water (Thern Inc., 2008). This technology has been awarded a grant for testing at three U.S. sites. After testing is complete, this technology will be ready to market. This is the first filtration system specifically designed for arsenic, rather than general contaminants or metals.

Nanoparticles are another new technology that is being examined as a potential candidate for arsenic removal in water and wastewater (American Chemical Society, 2006). Activated Alumina is the latest type of polymer bead is infused with iron oxide in an attempt to develop a one-step coagulation process for arsenic removal in drinking water (American Chemical Society, 2006). This technology is still under development and will be available in the future, as a potential answer to the arsenic problem at the Deloro Mine.

The primary technologies being used in arsenic removal rely on coagulation and particulate removal, by either sedimentation or filtration. Recent lowering the U.S. EPA standards for Arsenic in drinking water has sparked a surge in technology development (Siegel et al., 2006). Many of these new technologies are simply improvements on older processes. At a recent conference on arsenic technology, AdEdge technologies scored as the most efficient in removal of arsenic from drinking water (Siegel et al., 2006). Many of these new technologies are still in the pilot stage.

The bottom line is the provision of safe drinking water to the people. Older technology focused on total source reduction. This is a monstrous task at the Deloro site. New technology that focuses of point of entry into the home may prove the most promising solution in the future. Cost and other factors may effect this decision and the new units would have to prove effective. This prospect will have to be analyzed further before a decision can be made. These new technologies may hold the solution to arsenic removal at the Deloro Mine Site.

There are several new technologies that hold promise for increasing the amount of arsenic removed prior to reentry into the Moira River. However, these new technologies are as of yet untested, let alone field tested. Although new technologies such as nanoparticles and new filtration techniques hold promise, they are still in the research and development stage. It will be many years before they are ready to meet the needs at the Deloro Mine Site. New technology is not likely to be a reliable source to meet the current needs of the community surrounding the Moira River.

Methodology

Sampling technique plays a significant role in the results obtained and in the reliability of the sample results. The Deloro Mine Site has a continual internal monitoring process. The purpose of this sampling procedure is to verify, or demonstrate whether the results of self-reported sampling are reliable for the purposes of public safety. These results will be compared to posted results at various stages of the water treatment process.

One of the key considerations in taking water samples for the analysis of arsenic is the preservation of highly reactive constituents within the sample. Many factors can influence the preservation of arsenic and arseno-compounds in water samples. For instance, light, pH, temperature, available oxygen, organisms and other factors can alter arsenic levels in the sample from the time of collection to the time of analysis. Samples were collected using groundwater sampling procedures contained in "Ground Water Sampling Guidance-GD12"; Appendix B. This procedure is considered standards acceptable procedure for the preservation arsenic in groundwater.