CSense® in the News

Although platinum prices are at an all-time high, the processing of the precious metal remains a complex and costly affair where the quality of upstream processes known as Base Metal Refining (BMR) can have serious financial consequences in the profitability of the downstream Platinum Metal Refining (PMR) process. In order to make their BMR process more stable, predictable and efficient, Impala Platinum Refinery turned to CSense for help.


Figure 1: A simplified flow diagram of Impala’s processes

Impala Platinum’s Base Metals Refinery in Springs gets its raw material from the company’s mining, concentrating, smelting and converting facilities in Rustenburg. The BMR then removes as much of the base metals as possible and sends the PGM (Platinum Group Metals) concentrate to the PMR plant for further processing. The base metals are refined and sold separately to maximize the conversion of raw material into revenue (figure 1).

1.1. Background and project objective
We identified difficulties in controlling the pH in the first stage autoclaves, says Abdullah Khan, Project Manager, Impala Base Metals Refinery. Poor pH control has a serious and negative impact on the PMR processes. This meant that we had to decrease the base metals content (thereby increasing the precious metal content in the concentrate) and we could do that by controlling the pH and consequently improving the nickel and iron extraction efficiencies. After balancing the numbers, we decided that we would base the project on a 1-2% reduction of base metals in the concentrate through the effective control of pH.

Before going ahead with the project, the refinery did studies on the available data and realized that they couldn’t create an advanced control system based on this input. Previously, the pH was more or less controlled through the PLCs but this didn’t provide any data analysis facilities that could help predict future values. One of CSense’s control engineers created a model of the whole solution, which was then transferred as a blueprint onto CSense in a simulated environment. This demonstrated that the refinery had 80-90% of the logic correct and this later greatly decreased the commissioning period.

It should be noted, however, that while APC greatly assists the physical control, the experiential knowledge of those who know the process should be included in the control logic, adds Khan

From this study, it became obvious that CSense’s Advanced Process Control (APC) and rapid process troubleshooting facilities could help us improve the PGM concentration process in a complex, multi-variable environment, says Tim Spandiel, Impala BMR manager. But to improve the string of processes that focus on providing PMR with the quality of material they need to be effective, it was decided to start at the beginning (nickel leaching) as this would have the most optimum effect on those processes dependent on its output.


Figure 2: Truncated view of the BMR process flow diagram showing those processes benefiting the most from this implementation of CSense.


1.2. Process description
Figure 3 shows an overview of the process, which involved operators having to deal with numerous interdependent variables (pH, temperature, levels, pressures, etc.) on all the plant items. With operators having to juggle all these variables, it was easy for temperature and pH profiles, for example, to go beyond their set limits, says Spandiel. This affects our ability to remove as much as possible of the nickel from the solids and degrades the quality of all products downstream.


Figure 3: Process overview


Another important metal to remove (leach) in this process is iron, which has to be kept in solution and to do that, active pH control needs to be applied to the autoclave. Iron must be discarded with the nickel solution and can’t be allowed to contaminate the PGM solids since this can seriously affect PMR’s ability to process the concentrate we give them and it may even have to be recycled. The copper content of the matte also contributes to some complex reactions and in addition to all this, we can get wide variances in the matte supplied to us by the smelter and this contributes to a very difficult environment with respect to manual process optimization, says Spandiel.

1.3. What needed to be done

• Stabilize the pH to improve the leaching efficiency of iron and nickel – this would provide a better quality of PGM concentrate for PMR and other processes.
• On-line and real-time pH sampling would provide the degree of control required to help optimize the process but this is outside the realm of controllers. Another consideration is that pH can’t be measured inside the autoclave, so a special sampling pot was designed to address this sampling problem (the pot was designed by Johan Rademan of CSense Systems (Pty) Ltd.)
• High-pressure acid leach has complex reaction dynamics and this would have to be taken into account
• Simplify the control approach by manipulating acid addition to compensate for pulp density and product feed rate changes as well as changes in pH measurements

An advanced controller based on a hybrid of fuzzy logic technology and fundamental principles would address these requirements.

1.4. What was done
Over a period of 6 weeks (excluding consultation time) CSense Systems installed an APC solution that gave Impala BMR the level of control and optimization they were looking for in their nickel leaching process. The system relieved the operators of many decisions that were virtually impossible to make given the complex, variable and real-time nature of the processes in their charge.


Figure 4: Daily APC report and histogram showing pH and other variations


On the operational side it’s important that operators understand the process thoroughly and this requires on-going training for new personnel, says Sello Semosa Leach Plant Manager, Impala Base Metals Refinery. This is also true of APC systems. Those that don’t provide the appropriate level of control tend to be bypassed by operators who can do a better job. Here, pH is the control parameter and the CSense-based APC currently in use has resulted in operators trusting it and using it to their advantage rather than bypassing it. Another benefit is that the system allows us to change production schedules by looking after all the multitude of variables in a critical process.

The APC performance report (figure 4) and its accompanying histogram, showing variations from set points to actual performance, is e-mailed daily and automatically to qualified personnel giving management a near-real-time view of the efficiency of the BMR nickel leaching process on which so many other processes rely.

1.5. Realized benefits

• Through less iron and nickel content, the PGM concentrate grade is much improved
• From a performance analysis conducted in March 2007:
• The pH variation has been reduced from 1,2 to 0,7 (an improvement of 40% in pH stability)
• The nickel extraction efficiency has increased by 0,5%
• The iron extraction efficiency has increased by 3,3%
• The PGM grade has increased by 1,4%

Although these numbers may seem small, says Spandiel, they are extremely significant to the financial benefit of all our refining processes.


Other benefits include:

• A reduction in pH peaks in the autoclave, which can oxidize certain elements whereby they become difficult if not impossible to leach. These elements go right through the process and end up contaminating the PGM solids with the result that the entire batch has to be recycled through a lengthy and costly processing pipeline.
• Acceptance of the system by operating staff who now also trust it to do the right thing
• Stable process control in spite of variations (one specific batch of matte had an iron content of 11% instead of the usual 0,7% or less yet the system ensured that the PGM solids were within specifications).
• Indirectly limiting environmental emissions
• Real savings affecting Impala’s business bottom line

1.6. Conclusion
CSense’s intelligent APC and troubleshooting capabilities have shown their merit in this implementation to the degree that Impala has realized that there are many more opportunities for APC including application in:

• Temperature control of copper leaching
• Efficiently controlling the steam input to evaporators and crystallizers
• The precipitation of selenium and tellurium, which are two impurity components
• Jarosite precipitation, which is a process whereby iron is removed from the solution and turned into a solid state compound called Jarosite

Modern SCADA historians store a wealth of information but it’s making sense of it all that’s difficult, says Johan Rademan of CSense Systems, specially when dozens of interlinked and interrelated variables are involved. Optimizing processes by trial and error is simply not viable and the only alternative is systematic process troubleshooting and control.