EXTRACTION OF NICKEL WITH PRE-NEUTRALIZED ORGANIC ACIDS USING OUTOTEC MIXER SETTLER TECHNOLOGY

摘要

Good pH control is essential for selectivity in the extraction of metals using reagents that are organic acids. Common industrial reagents in this category are di(2-ethylhexyi)phosphoric acid, bis(2,4,4trimethylpentyl)phosphinic acid (the active compound in Cyanex~R272 by Cytec and in Ionquest~R 290 by Rhodia) and the tertiary carboxylic acids as the Versatic? Acid 10 by Hexion Specialty Chemicals. In order to avoid precipitation in the extraction apparatus, the reagents are often used partly pre-neutralized, e.g., by ammonia or caustic soda solutions. When these extractants are partly saponified, they start behaving like surfactants and form microermilsion and other aggregate structures. As the partly pre-neutralized solution is contacted with a metal-containing feed solution, the complexation takes place in a pseudo-homogeneous environment allowing fast extraction kinetics. The paper describes the theoretical basis of the phase behavior involved in these systems using the extraction of nickel with Versatic Acid 10 as an example. The paper reports how this phenomenon can be exploited in the Dispersion Overflow Pump (DOP~R) unit of the Outotec mixer-settler for nickel extraction with illustrations from pilot size experiments. The extraction process was visually followed by taking high-speed photos of the dispersion inside the DOP as well as by recording the rate of extraction based on chemical analysis of samples from the DOP outlet channel.