The effect of humic acids on MgO in the WIPP

Sara A. Mathews, Nathalie A. Wall, and Anna C. Snider

Sandia National Laboratories - Carlsbad Programs Group, 4100 National Parks Highway, Carlsbad, NM 88220, USA

The Waste Isolation Pilot Plant (WIPP) was excavated in a Permian bedded-salt formation and is a Department of Energy (DOE) repository for transuranic (TRU) waste from defense programs. WIPP received its first shipment of TRU waste in 1999. Premier magnesium oxide (MgO) is used as an engineered barrier in the repository. MgO reduces actinide solubility by consuming carbon dioxide produced from possible microbial action, buffering pH between 8-10, and reducing the amount of available water. Humic acids (HA) are issued from the degradation of animals and vegetation and are of colloidal size (0.001-0.1m m). HA may occur in the WIPP from soils contained in the waste or the degradation of organic matter present in the waste. The latest experimental results show that HA are stable for several months in WIPP brines; however, when MgO is present, the humic material precipitates completely. This presentation features x-ray diffraction analysis, as well as images employing scanning electron microscopy of MgO in the presence of and in the absence of HA.

This research is funded by WIPP programs administrated by the Department of Energy.

Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.