Silver proves precious for weapons disposal
15 Jan 2000
The ratification of the United Nations Chemical Weapons Convention (CWC - see News) has opened up new prospects for developers of specific types of process - those designed to destroy the stockpiles of chemical weapons held in the US and Russia. The US Army has developed several processes itself, based on incineration or treatment with molten metals. In Scotland, however, AEA Technology has high hopes that its Silver II process could also prove a money-spinner in this area.
Silver II is an electrochemical process, originally intended to destroy radioactive organic wastes from the nuclear industry. The process mixes the feed chemicals - which can contain virtually any organic compound - with a solution of silver I nitrate in nitric acid, then pumps this into the anolyte section of an electrochemical membrane cell, similar to those used in the chlor-alkali industry. Here, the silver ions are oxidised to silver II, which is one of the most powerful oxidising agents known. Operating in tandem with the nitric acid - itself a powerful oxidiser - the silver II ions attack the organic feed chemicals, oxidising them to carbon dioxide, water, and a mixture of inorganic salts. These have a low volume, and can be recycled within the plant or disposed of as `standard industrial waste', says AEA.
The reduction products - silver I, protons and water - diffuse through the membrane to the catholyte side of the cell. Here, an electrochemical reaction to balance the one on the anolyte side reduces the nitric acid to nitrous acid and NOx. Another section of the plant re-oxidises these compounds to nitric acid.
The Chemical and Biological Defence Establishment at Porton Down has been running a 4kW Silver II demonstration plant since last year, where it has destroyed the nerve gas known as VX mustard gas. Both compounds are held in the US' chemical stockpile. The process can also destroy conventional explosives, and combinations of chemicals and explosives, claims AEA.
