Investigating the effects of process parameters on the filtration performance of ferric hydroxide in a continuous MSMPR reactor

Abstract

Iron removal in the nickel industry is achieved by precipitation and filtration, and for enhanced process efficiency, the filtration step must be improved. A mixed-suspension-mixed-product-removal (MSMPR) reactor set-up operating at steady-state was established, simulating industrial conditions, and the effect of temperature and residence time on filtration performance of the precipitated akaganéite was investigated. Increasing the reaction temperature and residence time improved the filtration performance, where temperature had the most prominent effect, reducing the specific filter cake resistance with over one order of magnitude from 25 °C to 75 °C. However, there must be a trade-off between temperature increase and cost-effectiveness. A lower moisture content in the filter cakes was also observed with increasing residence time and temperature, which is advantageous in terms of handling of waste and for potential reuse of the iron precipitates. Elevated temperatures resulted in formation of particles with higher crystallinity, lower surface area and higher stability towards aggregation. These particle characteristics were explained by the significant decrease in supersaturation at steady-state at higher temperatures. Variation in residence times, on the other hand, did not affect the solution supersaturation but was still an important parameter on the particle characteristics, which in turn had implications on the filtration performance. The significant changes observed in specific filter cake resistance and filter cake moisture content, but not in supersaturation, with varying residence times were explained by internal rearrangements and locally induced ageing of the particles.