PNNL-Sequim maintains temperature-controlled natural seawater exposure systems for evaluating how well advanced technologies can extract critical minerals (e.g. lithium, uranium, and rare earth or transition elements) directly from seawater. These exposure systems consist of flow-through columns for small samples and fibers, 60 L recirculating flumes for larger braided adsorbents, and a 1,000 L raceway flume for testing of industrial scale adsorbent materials. These systems can supply either raw or filtered (through a 0.45 µm filter) seawater. Researchers can obtain typical coastal marine conditions, and control temperatures between ambient and 35°C and flow velocities between 0 and 10 cm/s.