Engineering & Mining Journal

JUN 2013

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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Page 113 of 171

GETTING MORE GOLD more positive (+), while presence of reducing solutions cause a negative (–) reading. ORP measurement therefore provides a direct indication of the oxidative strength of a solution. ORP Measurement In-Line ORP measurement is important during wet chlorination as it indicates when complete dissolution of the gold content of the slimes has been reached. Therefore, it prevents on the one hand, gold being carried in the raffinate, and on the other, excessive and costly chlorination. The oxidation potential is monitored by in-line ORP measurement. For reliability and accuracy purposes Mettler Toledo ORP measurement systems were installed. The high suspended particles content in wet chlorination can quickly interfere with the performance of ORP sensors due to particles forming a coating on the sensor's surface and process chemicals entering and poisoning the sensor's reference electrode. To counteract this, the chosen sensor features a non-clogging open reference junction and a solid polymer electrolyte that resist poisoning. To ensure the sensor is always operating optimally, it is used in conjunction with an automated cleaning system. Using a retractable sensor housing, the system automatically extracts the ORP sensor Figure 5: ORP measurement in-line. from the chlorination process to perform cleaning when required. The diagram in Figure 4 shows the integration of the EasyClean cleaning system into the measuring point. A real-time recording of the ORP measurements vs. H2O2 dosing is shown in Figure 5. Higher integrity of the measurement is obtained through the use of Mettler Toledo's Intelligent Sensor Management (ISM) concept. This technology comprises pH/ORP sensors with embedded microprocessors. One advantage of ISM is that the sensor output signal is fully digital and therefore cannot be corrupted by wet electrical connections, electromagnetic interference, or long cable runs. Another benefit is that ISM sensors feature predictive diagnostics. Thanks to these, measurement availability can be ensured at all times, as possible measurement problems are detected before they become significant. The sensor will, for instance, indicate how many days of reliable operating life are left so that action can be taken before the sensor fails. Several ISM pH sensors are installed in the side processes of the wet chlorination, all of which require very little maintenance time compared to conventional analog sensors. Competitive Advantage from ORP Measurement Figure 4: Illustration of the ORP measurement system. 112 E&MJ • JUNE 2013 Technology developments have reduced the production costs for all commodity metals over time at KUC, either through significant step changes, such as smelting and refining modernization, or by continuous improvement implementations, such as the anode slimes, wet chlorination operation described above. Through implementing multiple-step Six Sigma tools in processing of the copper anode slimes and the technology development of in-line, intelligent ORP measurement in the wet chlorination operation, the refinery has enhanced its productivity, produces higher quality copper, gold and other metals, and increased its profitability. For KUC, technology developments have overcome challenges, and sustainable competitive advantages have been achieved.

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