Permeable, subsurface sorbent barrier for 90Sr: Laboratory studies of natural and synthetic materials

Laboratory studies were conducted to identify the optimum sorbent material to use in the construction of a full-scale, in-situ sorbent barrier for intercepting a 90Sr plume within a surficial water-bearing sand and gravel layer. Evaluation of a set of materials for use as a passive sorbent wall was first approached through a series of batch sorption tests, using 85Sr tracer, on a set of natural zeolites and metal oxides to determine their effectiveness for sorbing 90Sr. Selected materials, based on their sorption capability in the screening experiments, were further tested in flow-through columns to assess hydraulic performance and sorptive characteristics under dynamic flow conditions. Test data were incorporated into a one-dimensional finite difference model and estimates were made of in-situ performance over extended time frames with respect to 90Sr breakthrough and loading on the barrier material. Several natural zeolites were found to remove 85Sr effectively from groundwater that contains 120 μg/ml of Ca, an element that can compete with Sr during sorption. A barrier wall of thickness 1.2 m was estimated to have a maximum life of about 10 years before replacement or regeneration of the sorbent bed is required.