484 in a mineral processing context), systematically differing only in the condition that is being tested. In production data, ‘similar’ data pairs are those that are adjacent in time, as these have the highest chance of comprising shifts where ore types, throughputs, operating strategies, etc. are ‘similar’. Therefore, comparisons would only take place between (for example) Monday night-shift and Tuesday day-shift. Comparisons would not take place between Monday night shift and (for example) Friday day shift, as the large time difference would likely result in different circuit, feed and operating conditions that would otherwise exacerbate data variability and further obscure the real effect of the trial. There will, of course, be variability within each data pair, as no two-shifts are ever identical. However, this is overcome in the experimental design by ensuring that the overall length of the trial is sufficient to allow the effect of the tested variable (if any) to be isolated from the inherent variability in the data. Furthermore, the application of the experimental vs. baseline conditions is randomised within each pair, to guard against any underlying time-based trends that may exist in the production data that would bias the outcome of the trial. For instance, in JKTech’s experience, it is common for recoveries during night-shift to systematically outperform those achieved during day-shift. To eliminate this source of bias, the trial condition is tested during both night and day-shifts, with the application changing randomly within a given pair (Figure 2). Figure 23 – Randomised paired trial design where a single ‘time-block’ corresponds to one day. In a recent JKTech study, the effect of a flash flotation cell treating cyclone underflow material in a grinding circuit was tested. The production data in Figure 24 is identical to that shown previously in Figure , except with baseline (flash flotation OFF) and trial (flash flotation ON) periods also indicated. Figure 24 – Feed grade (Pb %) and recovery during a flash flotation cell trial. The alternation of periods where the flash flotation cell was either ON or OFF is shown with the background grey line (high value = ON; low value = OFF). The objective was to assess whether the flash flotation unit was providing any benefit to Pb recovery, or whether it should be switched off permanently to simplify the process and reduce costs. Due to Baseline Trial Trial Baseline Trial Baseline Baseline Trial etc. Day 1 Day 2 Day 3 Day 4 Time 0 1 2 3 4 5 6 7 8 9 80 82 84 86 88 90 92 94 96 0 10 20 30 40 50 60 Pb feed grade (%) Pb recovery (%) Day Recovery (%) Feed grade
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