On-Line Technology for Continuous Measurement Concentration of Individual Chemical Elements

Cross belt analysers can help mining companies in Africa get real value from their mineral ore through accurate data, gathered continuously on-line in real-time on concentration of individual chemical elements at all stages of mineral processing. Crucial decisions can be informed by accurate data, improving recovery and reducing ore going to waste – all while acutely focused on Net-Zero targets and real reductions in carbon emissions

Increasingly, lower quality grade ore is being found in mining projects. While this is entirely out of their control, practically, what minerals and mining companies can manage is continuously seeking ways to increase efficiency, reduce cost, waste and emissions, and improve safety in their operations from pit to port.

Usually, pertaining to mineral processing operations, small improvements, if carried out scrupulously, cumulatively, can yield substantial gains. One of the avenues worth exploring is in techniques that can aid earlier collection of data on concentration of individual chemical elements at all stages of mineral processing. Then, the data gathered can give plant operators a better understanding of ore variability, which can be utilised to make informed decisions on improving efficiencies in process control for better metal recovery. Ultimately, valuable concentrations of metals would be recovered and prevented from going to waste, making processing lower grade deposits more efficient and economically viable.

The need for alternative technologies

Doubtless, conventional sampling methods, inherent with their shortcomings, would fall short of meeting contemporary expectations. Clearly, this necessitates for mineral processing companies to adopt alternative technologies whose efficacy has been thoroughly tested and consistently proven in rugged conditions. Interestingly, there is ample evidence suggesting that there are immense opportunities to be had for minerals and mining operations in adopting continuous, real-time, sensor-based devices for their ore grade assessment requirements. Installed over a belt, the devices measure mineral concentration levels, as well as other characteristics such as mineral species, continuously in real-time.

At the onset, the significance of real-time, continuous online analysis can be better grasped when one examines the limitations of conventional sampling methods and their impact.  Information from some of the leading suppliers in the field suggests that online analysers are filling the gap, and one would not hasten to state that it could just be the thing for industry – especially given a current focus on increased yield and efficiencies against a backdrop of sustainability and Net-Zero targeting.

The drawbacks of traditional sampling

There have been a number of case studies in which the comparison has been made to establish the reliability of traditional sampling methods, on the one hand, and real-time, continuous analysis, on the other, in capturing data on variability of chemical composition of coal at a coal washery in Australia.

Without question, amongst more recent studies, one whose findings have been referenced in global involved a conventional sampling method and Real Time Instruments’ AllScan, cross belt ore analyser. The AllScan employs Prompt Gamma neutron activation analysis (PGNAA), which penetrates through the depth of the material on the conveyor belt. In PGNAA, a neutron, based above or beneath the conveyor, generates neutrons that are absorbed by the material to reveal its elemental spectra.  Continuously, it measures what is on the belt through the cross-section, the full width.

The findings indicated that the AllScan excelled, producing detailed insight on process performance, the required data of ore on the conveyor belt consistently. On the other hand, the traditional sampling method fell short. In the most part, the traditional sampling method was erratic, producing patches of data of a limited scope, which, if utilised, could result in wrong decisions, leading to valuable concentrations of metals going to waste. This is the last thing a mining company would expect to experience. In an industry, where accuracy is the currency, techniques that rely on guesswork are a definite no-no.

Continuous, Real-time analysis: Convenience and Accuracy

Recognising the comparative advantages that real-time continuous, online analysis brings and the possibilities that it has opened, it is not surprising that the technique is gaining traction in the mining and mineral processing sectors. The main benefits which the technology offers are convenience and accuracy.

• Convenience

Cross belt analysers are convenient – scanning the material on the rock continuously, sending readings rapidly to process control and production management systems. Sometimes, if needs be, the data can be stored in the cloud for future retrieval. Above and beyond, the data can be sent to the mine, so that necessary adjustments to the mining operations can be made, if necessary.

• Accuracy

Ultimately, the online analysis can eliminate sample preparation errors caused by inherent bias common in conventional sample-taking methods. This ensures accuracy and integrity of the data gathered. Additionally, it decreases the total volume of samples that would have had to be taken within processing plant sections.

Opportunities for application

Ongoing research and development initiatives promise more opportunities opening up exploring the application of continuous, real-time, online analysis. To date, the use of online analysers, with reference to the AllScan, in ensuring that the ore from one stage to another is within specified parameters far earlier than other instruments has been ground-breaking.

The AllScan can also be used in slurry analysis – measuring the elemental concentration of the slurry as it passes through its measurement zone.

Usage in the back end of mineral processing, though not very common, merits highlighting. For instance, the analysers can be used in grade control, in particular, ensuring that only premier grade ore is shipped to markets. It is inconceivable to waste resources exporting inferior grade ore while an appropriate process could have been employed to forestall the lapse.

Industry uptake

As you would have thought, initially, the minerals sector had been hesitant to embrace continuous, real-time chemical analysis, opting to stick with the ‘tried and tested’ conventional sampling techniques. The coal and cement industries had enthusiastically taken the technology on board much earlier. Nevertheless, the need to ensure that their operations are sustainable has compelled mining companies to adopt real-time, continuous analysers. Currently, RTI has made over 100 installations of its AllScan worldwide, with a prospect of the portfolio growing.

In Africa, a South African manganese, chrome and iron miner, demonstrates the success of online analysers. The mining company has online analyser devices installed at some of its operations. Installation was done after a rigorous trialling process in a production environment in relatively new processes and plants. The analysers have been in processes from primary to final product bar product certification.

Worthwhile investment

By and large, real-time, continuous, analysers are a worthwhile investment, worth every dime of the high initial costs, when one takes a long-term view. Usually, after commissioning the cost could be recouped within a year, should the optimisation process be applied appropriately, states Micheal Edwards, RTI’s specialist for Africa Region..

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Case study at a Coal Washery

Recent studies have substantiated the effectiveness of real-time, continuous on-line analysis techniques over conventional ore sampling systems in more demanding conditions. A comprehensive study, carried out and concluded in 2015, lent further credence to this notion.

The use of data output value was opted as it was deemed simple and relatively reasonable. In the study at a coal washery in Australia, which treats a number of types of coal with widely varying ash content, the data output values of the two methods was compared, and the prominence of online analysers was established. The findings stake the claim for the application on-line analysers. The study, “Determination of the precision of sampling systems and on-line analysers” was presented at the 7th World Conference on Sampling & Blending, Bordeaux, France June 10-12, 2015.

Data values were collected from both an online analyser and a conventional sampling system producing assays every six hours.  The results confirmed a phenomenon all too familiar- as it was in previous studies.

The conventional sampling system was erratic in reading coal with different ash content. On the other hand, consistently, the on-line analyser was able to interrogate the feed coals on the same belt. The conventional sampling system data was analysed on a per coal type basis in order to pick up the serial correlation for those coal streams.

Ideally, a sampling system must be unbiased and very precise, accurate. Unfortunately, more often than not, with conventional sampling systems, sadly, it is futile to attempt calibrating an on-line gauge for coal ash and coal ash constituents against routine samples taken over the measurement. Thus, this rules out calibration again conventional sampling systems, which rely on guesswork and assumptions.

It is also worth mentioning that, in the niche market of continuous, real-time, online analysis, PGNAA analysers are more effective than other technologies. Alternative technologies such as Near-Infrared (NIR) and Laser Induced Fluorescence (LIF) are also used in online belt analysis.  These technologies emit energy to the surface of the material, whose characteristics are analysed based on how the energy is reflected back. Another technique is the XRF (X-ray fluorescence), which produces an intense X-Ray beam that causes different elements in the material to produce distinct fluorescence x-rays, an analysis is made of these rays. The drawback with these technologies is that they lack the ability to primarily read the surface, hence are limited as far as penetrating the cross section of the material is concerned, unlike PGNAA analysers.

Article adapted from a paper published at 7th World Conference on Sampling & Blending, Bordeaux, France June 10-12, 2015