Mercury Removal from Groundwater

A case study covering the removal of mercury from groundwater using ResinTech's SIR-200.

INTRODUCTION 

A client needed to supply a groundwater system that treats water from a flooded basement at
an industrial site. The system must discharge the treated water to a river. Discharging to a
surface water makes the effluent requirements much more stringent than sending the water
to a municipal sewer. 

The ion exchange portion of the project was for the removal of mercury. The feed water was
pH adjusted to between 6.5-8.5, which is high for using chelating resins such as the mercury selective ResinTech SIR-200. The proposed system was for a lead-lag configuration that would run at a flowrate of 4 gpm/cu.ft. The effluent requirement needed to reduce mercury levels
down to ppb level. 

CHALLENGE 

The client did not have a complete water analysis and did not have access to a water sample. The water analysis which was reviewed only contained the contaminants of concern, specifically the heavy metal concentrations. The water quality was expected to be typical groundwater with moderate total dissolved solids (TDS), and low levels of organic/metals contamination from the basement that is being pumped out. Additionally, the client was under an extreme time constraint; the system needed to be operational in a few months. 

The effluent of the ion exchange system would be diluted by a factor of 5 to 20 before reaching the outfall to the river. The client did not have a hydrogen sulfide (H2S )or sulfide limit but they did have a toxicity limit. (The toxicity test for discharge to natural waters is often the Ceriodaphnia Dubia test, EPA Method 1002.0).

PROPOSED SOLUTION 

The best option given the limited information seemed to be ResinTech SIR-200, a mercury selective hydrogen form macroporous weakly acidic cation resin. This product essentially precipitates the metals onto the resin as metal sulfides, achieving extremely low effluent levels. The system flow rate of 4 gpm/cu.ft. was faster than the recommended 1-2 gpm/cu.ft. on the Product Data Sheet. 

Additionally, the client had a concern using SIR-200 in an application where the water is released to a river due to the following phrase on the data sheet: Due to the possible release of low levels of H2S, SIR-200 is not recommended for use in potable water applications. 

A simple lab experiment was run to simulate mercury removal using the ResinTech SIR-200 resin. The test was performed at the higher that suggested flow rate of 4 gallons per minute per cubic foot. The effluent also checked for mercury as well as concentrations of sulfide and hydrogen sulfide. 

RESULTS 

The results, listed below in Table 1, show that no sulfide or hydrogen sulfide was detected in the effluent, even after an overnight soak. Mercury removal was virtually complete at the neutral pH even at the accelerated flow rate. 

CONCLUSIONS 

The bench study data resulted in a successful proposal and system design by the client. ResinTech SIR-200 was used to effectively remove mercury from a contaminated groundwater without contributing any undesirable leachables to the effluent. 

Table 1: Mercury Removal and Sulfide Throw ResinTech SIR-200