Investigations on the selective particle/oil-aggregation as a processing strategy for ultrafine particle systems

Difficulties in the selective separation and recovery of ultrafine or even colloidal particles (ranging from 0.1 to 10µm in size) represent a common problem in various industrial fields, e.g. in the mineral processing industry. The difficulties arise due to the dominance of surface effects over bulk properties that strongly determine the behavior of such systems. In order to overcome these problems various physico-chemical process approaches, based on differences in particle wettability and the use of a non-polar, water-immiscible oil phase, are reported in different investigations. For these oil-assisted separation techniques, differing only in oil amount, addition and function, particle/oil aggregates could be achieved theoretically with a high degree of selectivity either by (selective) particle accumulation at the oil/water interface or even by (selective) particle transfer from the aqueous pulp into the oil phase.

In this paper we present investigations on the selective particle/oil aggregation behavior for various ultrafine model particle systems (e.g. quartz, magnetite, apatite) and aliphatic oil phases of alkane basis. Analytical investigations performed include the analysis of zeta potentials of oil droplets and solid particles in modifying reagent solution and reagent-free solution, the particle/oil aggregate structure by particle image analysis as well as wettability characterization by contact angle measurements. Experimental investigations include separation experiments using a modified laboratory-scale flotation column for different artificial solid mixtures. In order to selectively control the particle surface properties, different modifying reagents, including sodium oleate, CTAB, sodium silicate, citric acid, etc. were chosen to promote particle/oil aggregation for various target particles and more importantly the hindrance of particle/oil aggregation for the others. The degree of selectivity achieved as well as recovery and type of oil/particle aggregates formed are presented with regard to operational parameters like pH, electrolyte content, oil/water volume ratio and oil droplet size.