Metals Remediation Compound (MRC®)

Product

Metals Remediation Compound (MRC®) removes metals such as dissolved Cr(VI) from groundwater via in situ immobilization (precipitation and/or sorption to soil particles). MRC consists of an organosulfur compound esterified to a carbon backbone. This organosulfur ester is embedded in a polylactate matrix, making MRC a thick, viscous liquid. Upon injection into an aquifer, the organosulfur compound (the active metals immobilization agent) is released in a controlled manner when the ester bonds in MRC are cleaved via hydrolysis and microbial enzymatic action. Similar processes also cause MRC to release lactic acid which provides a carbon source for naturally-occurring bacteria and creates the optimal conditions for metals immobilization by the organosulfur compound.

Purpose

To cost-effectively immobilize metals such as hex-chrome Cr(VI) from groundwater.

Functionality

MRC stimulates chromium immobilization using a two-part mechanism:

  1. The organosulfur compound in MRC is a direct chemical reductant for soluble Cr(VI) and produces insoluble trivalent chromium (Cr(III)).
  2. MRC can stimulate Cr(VI) reduction indirectly by providing lactic acid, which is rapidly metabolized by subsurface microbes and creates reduced species, like ferrous iron and sulfide which are known to chemically reduce Cr(VI) to the insoluble Cr(III) state.

The Added Benefit of Reductive Dechlorination

MRC can also be used to treat sites with mixed hexavalent chromium and chlorinated hydrocarbon contamination because it provides the substrates needed to facilitate dissolved hexavalent chromium immobilization and reductive dechlorination. The dual-purpose feature allows MRC to effectively treat sites with co-mingled plumes because it eliminates the need for separate technologies to treat metals and chlorinated compounds. The organic substrate and lactate present in MRC accelerates the in situ biodegradation rates of chlorinated hydrocarbons (CHs) via anaerobic reductive dechlorination processes. Reductive dechlorination is one of the primary attenuation mechanisms by which chlorinated solvent groundwater plumes can be stabilized and/or remediated.

Geochemical Factors to Consider

Within the subsurface environment, dissolved metals are affected by a number of geochemical factors including pH, electrical potential (Eh), complexation, sorption and ion exchange. The ability to manipulate and control these factors can directly influence the physical state, mobility, and presence of metals in groundwater through processes such as precipitation, oxidation/reduction, sorption, and complexation.