THE DETERMINATION OF TRACE METALS IN CONCENTRATED BRINES FOR PROCESS CONTROL

Abstract

The determination of the alkaline earths in concentrated feed brines is required for process control purposes in the chlor-alkali industry. Methodology was developed, based on ion-exchange chromatography, for the determination of alkaline earths in 30% sodium chloride. Brine samples were loaded onto a dynamically coated chelating ion-exchange column. The column selectively retained the analytes of interest while allowing the matrix to pass through unchanged. This allowed the simultaneous preconcentration of the analytes and matrix removal. Following the preconcentration step, the retained metals were backflushed from the column, using a lactic acid mobile phase, and separated by cation exchange chromatography. Detection was based upon inverse photometry using a post-column reagent composed of the chelating dye calmagite and a solution of magnesium ethylenediamine tetra-acetic acid. The eluting metals displaced the magnesium which subsequently complexed with the calmagite. The decrease in absorbance, at the absorbance maxima of the dye was monitored.