THE ROLE OF QUATERNARY AMMONIUM COMPOUNDS IN STABILISING SODIUM OXALATE IN BAYER LIQUORS

Stabilisation of sodium oxalate in solution under certain conditions is a key control parameter for many alumina refineries. In an effort to increase oxalate stability and thereby improve process control, a family of quaternary amnmonium compounds has been identified as powerful liquor oxalate stabilisers. One of these has been used as the basis for development of the reagent Nalco 138. Throughout the quaternary anmmonium family of compounds, there are a number of clear structure/activity relationships which determine the stabilisinig efficiency of a particular compound. These relationships give some indications of possible stabilisation mechanisms and point to a greater understanding of oxalate stability. Total oxalate control is afforded by elimination of these compounds from the Bayer circuit by thermal degradation. The mechanism of this breakdown is shown to be via a Hofmann elimination reaction.