The Savannah River Laboratory has developed a procedure for controlled low-temperature chemical denitration of acidic solutions. The procedure can be used in semi-continuous denitration facilities and can also be directly applied to nitric acid solutions in a storage tank (in situ denitration) if there is some provision for moderate heating (up to 80/sup 0/C) and cooling. The procedure works well for both highly acidic (approx. 11M) and moderately acidic (approx. 3M) solutions. Trioxane, the cyclic trimer of formaldehyde, is used to initiate the reaction, while the bulk of the denitration is effected by the formic acid. Once initiated, the off-gas rate is controlled by the formic acid addition rate and can easily be maintained within the capacity limits of the off-gas system. The procedure was successfully applied to a plant-scale in situ denitration at the Savannah River Plant.