The physical chemistry of the precipitation stripping process for removing iron (III) from carboxylate solutions with dilute Sulphuric Acid

Abstract

Precipitation stripping is a single-stage process for stripping a metal from a loaded liquid cation exchanger with dilute mineral acid while simultaneously precipitating a hydrolyzed phase. The process has potential applications for removing iron from hydrometallurgical process streams; iron (III) can be stripped from carboxylate solutions with dilute H 2SO 4 (10–40 g/l), at 100°C under atmospheric pressure, to give goethite or basic sulphates. Experimental results for precipitation stripping are summarized. The thermodynamics of the process are examined and equilibrium constants for the precipitation stripping process are estimated at 25°C and 100°C. For the formation of goethite and hematite, these constants are very high at both temperatures. This indicates that iron (III) can only be extracted in reasonable concentrations by carboxylic acids before precipitates have nucleated, or when the metastable phase Fe (OH) 3 is present. The sluggish kinetics of Fe(III) hydrolysis and precipitation favour extraction at 25°C. At 100°C, however, goethite and hematite precipitate more rapidly, which drives the precipitation stripping process to near completion. The structure of the iron carboxylate complexes within the organic phase is discussed, along with the influence of these structures on the kinetics of stripping and the nature of the hydrolysis products.