Modern Mining August 2015

PROCESSING

Vertical ring WHIMS machines can boost chromite recovery

According to Multotec Process Equipment, its vertical ring Wet High Intensity Magnetic Separator (WHIMS) technology is proving effective in recovering the fine chromite in Platinum Group Metals (PGM) tailings. T he need exists to separate platinum group metal rich silica and chrome as the first step in PGM benefici- ation. The material is then

milled even finer and the platinum is separated from the silica, commonly using flotation. Tailings in South Af- rican operations typically contain a large portion of unrecovered chromite, which can range from 8 to 20 % by mass and 80 % passing 100 microns. While this is fairly well liberated, with the minus 1 000 to plus 115 microns being recovered by spirals,

Below: The Longi-Multotec verti- cal ring WHIMS machine for paramagnetic mineral beneficiation.

to date there has been no proven technology with which to recover the fine chromite. Due to the fact that the chromite is paramag- netic rather than ferromagnetic, a very high force factor is required to attract this material. The Longi-Multotec vertical ring Wet High Intensity Magnetic Separator (WHIMS) now offers PGM tailings operations the ability to recover this chromite, says Willem Slabbert, Application and Process Manager at Multotec Process Equipment. WHIMS is a well-known and proven tech- nology across a range of commodity sectors having been extensively used in haema- tite beneficiation, in the recovery of ilmenite in minerals sands applications, in manganese benefi- ciation, copper beneficiation and pyrite scavenging. The applica- tion for the recovery of chromite is fairly new and Multotec is currently involved in extensive test work. Magnetic field intensity is measured in Gauss and the field gradient is measured in units of Gauss change per mm. The field Above: Slimes dam ultra fine chrome separated from PGM containing silica with a Longi-Multotec vertical ring WHIMS machine.

44  MODERN MINING  August 2015