R.A. Acey, G.R. Jordaan, P.H. Nguyen, H. Nguyen
Keywords: metal remediation, metal recovery
Summary:We have developed a novel technology for the removal/recovery of heavy metal from aqueous and organic solvents. The patented technology is based on a low molecular weight protein known as metallothionein (MT). The protein has the unique ability to selectively bind a number of toxic/precious metals including, but not limited to, lead, mercury, arsenic, copper, gold, platinum, and uranium. The protein does not bind biologically essential metals such as sodium, calcium, or magnesium. We have cloned the MT gene, expressed the protein in bacteria, and developed a simple, cost effective purification procedure. We have been able to link the purified protein to an agarose based resin. The resin-MT complex functions as a “metal sponge”. As a solution contaminated with metal, e.g., cadmium, passes through the resin, the MT binds the metal. Water exiting the “sponge” is now metal free. If one were interested in recovering precious metal such as gold from a solution, the resin would be rinsed with weak acid to release the metal from the MT. The resin is reusable. The technology is also compatible with removing metal from seawater. MT was added to an aliquot of seawater containing 100 ppt (parts per trillion) of 109Cd. The MT metal complex was collected on a water permeable filter and counted for radioactivity. Greater than 90% of the metal was removed from the sea water using this technology. The technology is also capable of extracting metal from organic solvents. For example, we have been able to extract Pd nanoparticles from chloroform. As such, we have adapted our metal sponge technology to the recovery of uranium from spent nuclear fuel. We first extract the uranium from nitric acid using tributyl phosphate in Varsol as a chelator. The organic solvent is than extracted with a solution of MT where the metal is chelated by the protein. Subsequently, the metal can be recovered from the MT for disposal.