Removal of Chloride from Acidic Solutions Using NO₂

Abstract

Chloride (Cl -) salt processing in strong acids is used to recycle plutonium (Pu) from pyrochemical residues. The Savannah River National Laboratory (SRNL) is studying the potential application of nitrogen dioxide (NO 2 ) gas to effectively convert dissolved pyrochemical salt solutions to chloride-free solutions and improve recovery operations. An NO 2 sparge has been shown to effectively remove Cl -from solutions containing 6-8 M acid (H + ) and up to 5 M Cl -. Chloride removal occurs as a result of the competition of at least two reactions, one which is acid-dependent. Below 4 M H + , NO 2 reacts with Cl -to produce nitrosyl chloride (ClNO).Between 6 M and 8 M H + , the reaction of hydrochloric acid (HCl) with nitric acid (HNO 3 ), facilitated by the presence of NO 2 , strongly affects the rate of Cl -removal. The effect of heating the acidic Cl -salt solution without pre-heating the NO 2 gas has minimal effect on Cl -removal rates when the contact times between NO 2 and the salt solution are on the order of seconds.

Reducing chloride corrosion of stainless steel in the nuclear fuel manufacturing industry : an electrochemical-environmental perspective

“…Recent research performed at the Savannah River National Laboratory in South Carolina revealed that chloride can be effectively oxidized to chlorine gas in nitric acid using nitrogen dioxide [33]. The experiments were performed at various hydrochloric/nitric acid concentrations to determine whether chloride was removed from acid solutions due to the nature of the strong acid or due to the use of nitrogen dioxide gas sparging.…”

“…Nitrosyl chloride gas was the dominant gas produced when the acid strength of the solution was below 4 M. However, nitrosyl chloride gas could only be produced when a constant flow of nitrogen dioxide was sparged through the solution. For acid concentrations ranging from 5-10 M the dominant gas produced was chlorine gas [33]. Again, this reaction required a constant flow of nitrogen dioxide through the solution.…”

“…The oxidation of chloride ions in the acid solution occurs as a result of the formation of nitric oxide, which is a strong oxidant (see Section 2.3.3). Nitric oxide is produced when nitrogen dioxide reacts with water [33]: It is important to note that the stoichiometry of the chloride oxidation reactions observed by Pierce et al…”

Performance of Ti/Pt and Nb/BDD anodes for dechlorination of nitric acid and regeneration of silver(II) in a tubular reactor for the treatment of solid wastes in nuclear industry

“…Under industrial conditions, concentration of chloride ions in nitric acid can reach 1 mol L -1 [9,10] whereas for the dechlorination process the final concentration should be lower than 10 -3 mol L -1 to avoid AgCl precipitation when AgNO 3 is introduced. The rate of reaction (1) may be controlled by charge transfer or mass transport depending on the applied current density, chloride concentration, and hydrodynamic conditions which may depend on the rate of gas evolution at the anode [11].…”

“…Although a chemical process of chloride removal from pyrochemical residues by sparging nitrogen dioxide in the solution was proposed by Pierce et al [9], the implementation of an electrochemical process involving direct chloride oxidation can be considered as a simpler technique [8,10]:…”