Steelhead Specialty Minerals produces the naturally occurring zeolite minerals clinoptilolite TSM-140, chabazite TSM-300 and phillipsite TSM-180 from high-purity deposits in the western United States. These zeolites have the ability to capture cesium 134, 137 and strontium 90 isotopes and are ideally suited for the treatment of liquid radioactive waste effluents and in the design of sorbent barriers. The inherent properties of these minerals include a high cation exchange capacity (C.E.C.), appropriate cation exchange kinetics, resistance to attrition and ionizing radiation.
Users of Steelhead Specialty Minerals’ products include the British Nuclear Fuels Ltd. Site Ion Exchange Effluent Plant (SIXEP), West Valley Nuclear and the Oak Ridge National Laboratory Process Waste Treatment Plant. Low- and intermediate- level liquid wastes generated at these plants are cycles through highly-selective ion exchange columns packed with the natural zeolites. The zeolites significantly reduce concentrations of cesium and strontium to levels below mandated discharge limits. In addition to achieving decontamination objectives, the immobilized ions in the spent zeolite can be easily handled and, as in the case of SIXEP (see illustration), be economically encapsulated in cement.
Both natural and synthetic zeolites have been utilized for over a decade in other radioactive waste management programs at Hanford, Washington; Savannah River, South Carolina; the Idaho National Engineering Laboratory; and the General Electric Laboratory in Morris, Illinois. Applications include the removal of cesium from high-level waste water, and fixation of radioactive waste for long term storage. An important consideration in favor of natural zeolites is their low cost relative to the synthetic analogues.
In addition to treating radioactive process waste water, natural zeolites are being utilized in the construction and design of sorbent barriers. These permeable barriers employ sorbent material including natural zeolites and activate carbon to selectively contain low-level contaminants percolating from shallow land burial sites. Thee zeolites are combined with clays and other materials that retard the migration of the leachate long enough to allow exchange or decay of the radioactive ions. Water passes through these systems at rates that will allow uptake of soluble radionuclides but prevent ponding or the so-called “bathtub effect”.
Sorbent barrier systems designed at Battelle’s Pacific Northwest Laboratory eliminate the need for, and the expense of, long-term maintenance of shallow radioactive waste burial trenches. Additional applications of zeolites in sorbent barriers include: 1) a top cover to prevent contaminant uptake by vegetation; 2) an inner layer within a leachate/liner trench designed to produce a cleaner leachate; 3) backfill surrounding above- or below-ground storage vaults, to prevent contaminant release should a breach occur in the primary storage container.
TSM - 140 Clinoptile Zeolite Data Sheet 211
Sellafield/Performance of Sixep
Dontamination Ration 1:2000