625 The simulations indicated a 4% increase in gold recovery when the SK240 cell was added to the flowsheet (Pre_Sim #1), taking feed from the regrind cyclone underflow, as shown in Table 2. However, the copper grade in the final concentrate decreased from 29% in the base case to 27% (Table 3). These results highlighted the need to reduce the mass pull in the flash cell to improve the quality of the copper concentrate. Simulation 2 (Pre_Sim #2) addressed this by applying a lower froth recovery factor, which reduced mass pull and suggested that moderating flash cell recovery could limit pyrite recovery and gangue entrainment, thereby improving concentrate grade. Overall, the simulation results indicate that incorporating a flash flotation unit into the regrind circuit has the potential to improve gold recovery without significantly increasing the risk of diluting the copper concentrate. Copper recovery remained unchanged in the simulation, although it is expected to increase in practice alongside improved gold recovery. When considered together with the laboratory and pilot‑scale test results, the simulation outcomes suggest a strong likelihood of success for the project should it proceed to implementation. 5. EVALUATION OF SK240 INSTALLATION ON GOLD AND COPPER RECOVERY In 2024, site personnel completed a comprehensive technical and economic evaluation of the project, integrating outcomes from laboratory testing, pilot-scale trials, and process simulations. This assessment supported the selection and subsequent procurement of a Metso SkimAir® 240 unit (SK240) for installation in the circuit. Project delivery was executed by a multidisciplinary team, including site metallurgists and mechanical, electrical and process control engineers, working in close collaboration with operations staff to ensure seamless integration of the new equipment. Installation was finalised in early 2025, and the plant successfully entered full-time operation following commissioning on 13 March 2025. 5.1 Process performance analysis Several comparative evaluation methods were applied to assess changes in copper and gold recovery following the installation of the SK240 flash flotation cell. A summary of the key findings is presented below. A paired t-test was performed on a limited commissioning dataset comprising shift‑based operating data in which the SK240 cell alternated between online (ON) and offline (OFF) modes. The analysis demonstrated a statistically significant improvement in gold recovery when the SK240 was operating, with an uplift of at least 1% at the 90% confidence level. No statistically significant difference in copper recovery was detected between the ON and OFF conditions at the same confidence threshold. These results indicate that the SK240 delivered measurable gains in gold recovery without adversely affecting copper recovery during the commissioning phase. Multi-linear Regression Analysis was conducted on a set of operational data collected between January and July 2025. The regression results indicated that the operation of the SK240 flash flotation cell had a statistically significant positive effect on both gold (1.062 ± 0.736) and copper (0.517 ± 0.285) recovery at the 90% confidence level, confirming that the recovery improvements observed during commissioning were sustained under normal operating conditions. Comparison of Regression Lines was performed by comparing regression lines of gold recovery versus gold feed grade for SK240 ON and OFF conditions. This evaluation detected a highly significant improvement in gold recovery when the SkimAir® was operating (P‑value = 8.43 × 10⁻¹⁰). The mean improvement in overall gold recovery was estimated at 1.99 ± 0.53% at the 90% confidence level. In addition, pulp chemistry surveys conducted by site personnel indicated improvements associated with SK240 operation, including more favourable pulp chemistry and reduced oxygen demand. These observations suggest that the presence of the SK240 may create conditions conducive to downstream sulphide flotation using xanthate collectors. The effect is likely linked to reduced ferric ion activity and enhanced dixanthogen stability within the pulp, promoting more selective sulphide mineral recovery.
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