Abstract
Confined bed comminution in high-pressure grinding rollers (HPGRs) and vertical roller mills (VRMs) was previously used preferably for grinding comparably homogeneous materials such as coal or clinker. Meanwhile, it started to complement or even replace tumbling mills in ore beneficiation with ore and gangue particles of rather different breakage behaviors. The selectivity in the comminution of a mixture of particles with different strengths but similar particle size distribution (PSD) of the constituents in a particle bed was investigated earlier. The strength of a material is, however, also a function of particle size. Finer particles tend to be more competent than coarser ones of the same material. In industrial ore processing using confined bed comminution, this effect cannot be neglected but even be exploited to increase efficiency. This paper presents research results on this topic based on experimental investigations with model materials and with natural particles, which were stressed in a piston–die press. It appeared that the comminution result substantially depends on the material characteristics, the composition of the mixture and the PSD of the constituents. Conclusions will be drawn for the future applications of selective comminution in mineral processing.
Highlights
This study investigated the selectivity in the confined bed comminution of mixtures of narrow fractioned glass and corundum balls as well as of mixtures of quartzite and
For those artificial and natural materials, it was shown that the size
This study investigated the selectivity in the confined bed comminution of mixtures strength effect plays an important role in selectivity in confined bed comminution
Summary
The worldwide trend towards increased resource consumption, mainly driven by rising living standards of a growing world population, is unbroken [1,2]. The various phases in coal, limestone or clinker, exhibit a rather uniform fracturing behavior, at least compared with many ores This means that the progenies of particles of the same-size report, with a certain scatter, to the same-size fraction, if the particles are stressed with the same load. Since HPGR were initially used mainly in the cement industry, selectivity in confined bed comminution was of limited interest and, respectively, only occasionally investigated. It came into the focus when the mining industry started to accept HPGRs for ore grinding and forms a core part of the Grade engineering idea promoted more recently by the CRC ore initiative [14,15]. It can even be used to efficiently produce a pre-concentrate just by screening
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