Design and measurement of small recovery gains: A case study at Raglan concentrator

The appearance of a significant amount of liberated fine pentlandite in the Raglan tailings, during a campaign to demonstrate future ore behaviour, called attention to a recovery opportunity. This opportunity was identified by a statistical benchmark survey of the operation during that campaign, and QEMSCAN measurement of these survey samples. This development was caused by escalating ore treatment rates and different characteristics in future ore sources. It was thus proposed to change the selection of collector from potassium amyl xanthate (PAX) to potassium isobutyl xanthate (PIBX). Laboratory scale flotation testwork, using high-confidence flotation testing, followed. The PIBX showed much faster flotation than the PAX. Nickel yield to first rougher concentrate was increased from 23.5% to 44.2%. The Raglan flowsheet bypasses this first rougher concentrate directly to final concentrate. Thus there was an expectation that overall performance would improve at plant scale when using PIBX. A designed plant trial was implemented in 2007 to measure and confirm the performance gain. This trial design used on–off switching following a 3-month baseline data block of normal operations using PAX. This layout provided checking of standard PAX performance prior to and during the trial. Thereafter, they were used to evaluate the trial blocks using PIBX. This trial format was deliberately designed so as to overcome the effects of autocorrelation in the operations data. In this way, small but significant metal recovery gains may be measured and proven in a plant trial. The paper describes the case study to show that this approach successfully blocks out autocorrelation in time, which is an obstacle in analysing concentrator operations data. The results showed that the PIBX had produced clear and statistically significant recovery gains for Ni, Cu, Pt and Pd. Adjusted for feed and concentrate grades, these recovery gains were: Ni: 1.04%, Cu: 1.01%, Pt: 2.67% and Pd: 1.79% in absolute terms.