Automated process analysis and sorting

PROCESS CONTROL TECHNOLOGY

Automated process analysis and sorting

Sophisticated control of phosphates production is now possible thanks to the availability of real-time process analysers. The emergence of laboratory robots is also improving process efficiency and delivering cost savings.

Optimising production, driving down costs

Cost reduction and revenue generation have become increasingly important imperatives in the manufacture of phosphate fertilizers.

Producers are operating on relatively tight and volatile margins. In the second-quarter of this year, for example, North American producer Mosaic achieved an adjusted gross margin of £91/t on an average diammonium phosphate (DAP) selling price of $575/t. That compares to a margin of £129/t for the same period in 2023.

Today’s operating environment means there is now more pressure than ever for phosphate producers to cut their operating costs. This, in turn, requires a much greater degree of process control. Yet fine tuning the phosphates production process remains a challenge.

Traditional laboratory methods for analysing the grade (P 2 O 5 content) of mined phosphate rock, rock concentrates and chemical plant feed materials are time-consuming and labour intensive. The length of time taken between sample collection and the delivery of results also limits their usefulness in process control at phosphate mines and beneficiation plants.

Infrequent and intermittent sampling also means that lab test results are not always representative. Because of this, lab-based analysis is generally only able to provide a fragmented, incomplete picture of the production process.

Typically, phosphate fertilizer producers can only rely on getting lab results every 4-6 hours, meaning that process stages such as phosphate rock mining, froth flotation and phosphoric acid reactors are effectively flying blind when it comes to P 2 O 5 feed control.

North American Geoscan-M installation for monitoring beneficiated phosphate – with a TBM moisture analyser in the foreground.

PHOTO: SCANTECH

It is therefore unsurprising that phosphate plant operators are increasingly adopting automated on-line technologies for process and feed control at mines and beneficiation plants. These generate results rapidly, often in near real-time, and deliver tangible benefits in terms of improved phosphate plant efficiency and yield.

They can also deliver surprisingly quick returns on investment. For a typical beneficiation plant, an improvement in P 2 O 5 recovery of just two percent, for example, can deliver annual savings of half a million dollars, according to some calculations.

A range of automated analytical systems for process control in the phosphates industry are reviewed below. Many of these technologies are also applicable to potash mining and processing.

Laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been developed for monitoring and control applications in mining and mineral processing. One advantage of LIBS is its ability to detect and measure light elements, unlike conventional analytical techniques such as XRF analysis. The technology can be installed to analyse dry granular materials on conveyor belts or slurry materials.

The MAYA on-line laser analyser, a LIBS-based system manufactured by LYNCIS, provides direct, safe, efficient and accurate elemental analysis of phosphate and potash on conveyor belts.

LYNCIS has considerable experience in manufacturing on-line analysers for phosphate, potash and NPK fertilizer analysis. The company’s first LIBS analyser for the fertilizer industry, installed on a phosphate ore conveyor for The Mosaic Company in 2008, enabled removal of rock with high levels of impurities in real-time. Since then, the technology has proved to be widely applicable with LYNCIS successfully supplying LIBS-based systems for a range of industrial materials. Advantageously, the company’s state-of-the-art optical system allows the analysis of solid materials, slurries and brines with a high level of confidence.

LIBS offers the following advantages compared to other technologies, according to LYNCIS:

• The use of lasers is much safer with no harmful neutron, gamma or X-ray radiation
• Maintenance costs are very low
• Their calibration remains stable over a long period of time, eliminating the need for frequent recalibrations.

LYNCIS analysers have the following applications in fertilizer production:

• Ore quality control based on elemental analysis (P, K, N, Mg, Ca, Si, Al, Fe, etc.)
• Real-time adjustment of flotation reagent dosage to increase P 2 O 5 recovery
• Real-time adjustment of water dosage during the hot leaching and crystallisation of potash
• Product quality control.

In a major milestone for the company, LYNCIS is supplying five LIBS analysers for BHP’s massive new Jansen potash project in Saskatchewan, Canada. These will provide real-time chemical composition data throughout the potash production process from mining to final products. This real-time monitoring will enable rapid process interventions and ensure that final product quality is not compromised. Jansen Stage 1 is expected to produce approximately 4.35 million t/a of potash, once fully ramped-up. BHP is planning to double Jansen’s total capacity to 8.5 million t/a under the subsequent Jansen Stage 2 expansion.

LYNCIS recently developed a second generation of slurry analysers. These incorporate technical design changes, made in response to practical field observations, that improve the stability of on-line process analysis. These next generation analysers can be adopted by any project as they are compatible with third-party samplers and multiplexers.

LYNCIS MAYA 4L LIBS-based analyser.

PHOTO: LYNCIS

In general, there are two main end uses for LIBS process analysers supplied by LYNCIS:

• Sorting/impurity rejection
• Real-time production process control.

This is illustrated by the following four case studies:

Phosphate ore sorting. Two LYNCIS process analysers were installed on conveyors for The Mosaic Company to enable the removal of phosphate ore with high levels of impurities. Initially, these were used for real-time monitoring of phosphate content (as P 2 O 5 or bone phosphate of lime, BPL), impurities (MgO, Fe 2 O 3 , Al 2 O 3 ), the minor element ratio (MER) and the insoluble phase.

Finally, after an initial period of investigation, instantaneous LIBS measurements were used to reject impure, high magnesium phosphate rock (above two percent MgO). The investment in the LIBS system had a payback time of just 2-3 months, by avoiding penalties for off-grade product shipments and obtaining better prices for high-grade products.

For this application, a special high-sensitivity LIBS system was used to analyse and detect low-quality phosphate ore. This can contain just 3–7 percent P 2 O 5 due to contamination with gangue minerals. The use of a double-pulse technique with two synchronised lasers increased the strength of the emissions spectra from elements by up to eight times.

This double-pulse LIBS system is equally useful for analysing slurries – one example being the measurement of flotation reagent dosages in phosphate beneficiation. For this application, LIBS measurements have achieved a high level of accuracy and close correlation with standard laboratory analyses (R 2 = 0.91, average absolute error +/-0.75%), based on the collection and analysis of 256 samples over a six month period.

Potash process control. For real-time process control at a potash plant, a LYNCIS analyser was installed on a conveyor transporting wet cake after hot leaching and crystallisation. To enable continuous and automatic adjustment of the volume of water entering the process, this LIBS unit was also linked up to the water dosage system. Automatic dosage adjustments were then used to keep the concentration of the unwanted sodium chloride (NaCl) impurity in the process at exactly the permitted level. This is important as:

• Adding too little water would not remove the NaCl impurity
• Adding too much water, while producing a very clean, high-quality end-product, would lead to the unwanted loss of potassium chloride (KCl), the valuable target mineral.

In this application, the successful installation of a LIBS process analyser – for online detection of Na and K and automatic balancing of the process water dosage – improved the recovery of KCl at the potash plant by 0.4 percent. This translates to a cost saving of $1-1.5 per tonne.

Additionally, it eliminated the potential for penalties incurred as a result of poor product quality.

Potash quality control. LYNCIS recently secured a contract to supply a LIBS analyser for a potash conveyor at a Vancouver seaport. This will be used for final product quality control checks prior to ship loading. The new installation is expected to eliminate potential customer claims by maintaining product quality and ensuring this meets specified requirements. Product quality checks are required at various stages of potash storage and transportation, starting with grade sorting at the production plant warehouse and ending with the final quality control checks before loading shipping vessels. LYNCIS analysers are well suited to installation at seaports as they are robust and designed to resist corrosive, dusty and humid environments.

Polyhalite mining. LYNCIS has supplied LIBS analysers to a polyhalite producer. This unique multi-nutrient mineral fertilizer ensures balanced crop fertilization and promotes crop growth by supplying potassium, magnesium, calcium and sulphur. LIBS technology has proved to be very useful for stockpile homogenisation, mining grade control and impurity rejection at the polyhalite mine. Reliable and accurate measurement of all the valuable nutrients, as well as unwanted impurities, is possible as these generate strong LIBS spectra. Maintaining ore grade at the early stages of production, using a LIBS analyser to measure and control the relative concentration of nutrients and impurities, is worthwhile for the producer, as this prevents the use of costly reagents, water and energy that would be otherwise be required to process and upgrade the polyhalite ore.

Metso offers the Courier ® 8X LIBS-based analyser for on-line measurement of elemental concentrations in beneficiation plant feed, tailings, and concentrate slurries. This is the successor unit to the Courier ® 8 SL originally launched in 2013.

The Courier ® 8X has the capability to measure both light and heavy elements for monitoring and control in mineral processing plants, enabling the reduction of impurity levels in concentrates while maintaining the best possible recovery. Compared to the Courier ® 8 SL, the new LIBS unit offers:

• Best available technology with a diode pumped laser
• Improved temperature control, robustness, and serviceability
• Doubled measurement speed and 30 percent shorter cycle time
• Next generation Courier ® X software platform
• Remote support and calibration services
• Metso Metrics with KPI reporting for improved equipment availability
• Higher precision due to more stable slurry flow.

According to Metso, the Courier ® 8X maximises plant efficiency, using enhanced technology to measure light elements, and improves both recovery and reduces impurity content in flotation circuits. Its benefits include:

• Accurate monitoring of changes in feed mineralogy
• Improved control of concentrate quality
• Improved recovery through early detection of process disruptions
• Reduced need for time-consuming and labour-intensive manual sampling
• More efficient use of energy and raw materials.

Phosphates processing and concentration is one of the target markets for the Courier ® 8X SL. Its applications include:

• Final concentrate quality control: measurement of P content and Ca/P ratio
• Flotation recovery optimisation and reagent control: measurement of P in feed, concentrates, and tailings
• Measurement of ‘penalty’ elements: Mg and Si.

Prompt gamma neutron activation analysis

Prompt gamma neutron activation analysis (PGNAA) is a proven on-belt technology used for the real-time monitoring, bulk sorting and blending of ore materials on conveyors.

The GEOSCAN range of on-belt PGNAA analysers developed by Australia’s Scantech International have been widely-used for monitoring the quality of bulk industrial materials such as cement, coal and minerals since the 1990s. The GEOSCAN-M analyser is suitable for ore and concentrate analysis in the minerals industry, and enables operators to measure and control feed and product quality as well as improve process performance. There are more than 130 GEOSCAN analysers used in mining and processing plants worldwide, covering 15 commodities in total including iron ore, manganese, zinc-lead, bauxite and copper operations.

More than 20 GEOSCAN units are currently operating in the phosphate sector in Africa, the Middle East and the Americas. These rapidly deliver high quality process data to leading phosphate producers. Data quality is a critical factor, based on client feedback, as it provides plant operators with confidence when making process decisions. Digitalisation of conveyed rock enables data to be used for the forward control of feed in processing, feedback to mining operations, and for ore reconciliation to improve resource modelling.

GEOSCAN-M units are installed directly on the conveyor system, with the belt passing through the instrument’s analysis tunnel (see photo). Its compact design uses only one metre of belt space, enabling it to be fitted between standard idlers and avoiding any contact between the analyser and the belt or material. Three frame sizes are available to suit conveyor belt widths up to 2.4 metres and bed depths up to 0.53 metres. All material that passes through the analysis tunnel is continuously analysed and reported for a truly representative analysis. Being a fully penetrative analysis technique, it avoids many of the sampling errors and other issues associated with surface analysis methods or those which only analyse very small samples.

The segregation of materials during transport on conveyor belts commonly results in variations in quality between the top and bottom of the depth profile. This means that the results generated by sensing techniques which only measure the composition of surface materials, or those at intermediate depths, are unlikely to be representative of the composition of the whole bed. This kind of segregation on conveyors – and the resulting variation in the quality with bed depth – has been found to occur in most commodities where companies have investigated this.

The PGNAA technology in GEOSCAN-M installations emits neutrons from a californium-252 source located below the conveyor. These are absorbed by elements in the material being conveyed, with each element emitting a unique gamma ray spectrum.

The resulting spectra are captured by a sensitive detector array positioned above the conveyor and then processed using proprietary software. This generates independent multi-elemental chemical analyses (Ca, P, Mg, S, C, N, Si, Al, Fe, Ti, K, Mn, etc.) using calibrations customised to each site installation.

GEOSCAN units then report these to the plant operator – typically every two minutes – where they are interpreted to make process decisions. Results are combined with microwave measurements which detect and report moisture content.

For materials flowing on conveyors, GEOSCAN systems provide the shortest measurement time, highest precision and the lowest detection limits of any comparable measurement technology available on the market, according to Scantech’s client feedback.

The main applications and benefits of PGNAA systems such as GEOSCAN in phosphate mining and processing include:

• Measuring beneficiation feed quality for plant control
• Sorting phosphate rock received at chemical plant stockpiles
• Blending to improve feed quality and meet specification
• Blending acid reactor feed
• Controlling sulphuric acid additions to the acid reactor, based on phosphate rock feed chemistry, to maximise P 2 O 5 recovery, recover Ca to gypsum, and optimise acid consumption.

Scantech supplied its first GEOSCAN unit to the phosphates industry in 2014. This followed the company’s success with numerous installations for a variety of other mineral commodities, as well as test work on client phosphate samples to verify measurements and equipment performance.

The first phosphate industry analyser supplied by Scantech proved itself capable of delivering real-time phosphate process control with positive outcomes, based on frequent, high quality, reliable analysis results. Since then, Scantech has expanded into all the major global phosphate markets with more than 20 phosphate installations contributing to its total of more than 1,400 analysers in 80 countries worldwide.

A Middle Eastern customer, for example, has been able to obtain greater plant stability, and reduce the costs and delays associated with laboratory analysis, by installing a GEOSCAN unit close to the front end of their process. The delivery of PGNAA results every two minutes has enabled this production site to make process control decisions in real time.

An American phosphate complex also has a unit installed on the feed to their chemical plant. The customer uses GEO-SCAN data to increase yields by actively controlling their acid reactor process, as well as controlling the phosphate feed to the plant. As a consequence, this GEOSCAN installation has enabled the company to make some very significant production gains.

Such process improvements and production cost reductions are not always widely publicised, according to Scantech, even when a 20 percent increase in throughput or more has been achieved by some phosphate producers within a month of installing a GEOSCAN unit.

PGNAA systems like GEOSCAN offer a number of advantages for on-belt analysis, suggests Scantech, relative to other automated analysis systems:

• Comprehensive measurement: across the full cross section continuously with 6 monthly standard calibration checks and improved accuracy as more material is measured
• Deep penetration: through the entire bed depth
• Full-flow capability: tonnages limited only by belt size and depth (from 100 t/h to around 17,000 t/h)
• Reliable analysis: no mineralogy or matrix effects (Ca, Fe), unaffected by layering, particle-size, dust and belt speed
• Low maintenance: analysis uses solid state components, is low cost, noncontact, with remote access for calibration support and troubleshooting
• Local support: staff located in each major region.
• Easily combined with other sensor technologies: for moisture analysis and PSD (particle-size distribution), also available from Scantech.

Following a successful recent evaluation, Scantech can now offer GEOSCAN-M PGNAA for slurry analysis, delivered over shorter time-scales and at higher precisions than previously available on the market. The analyser can see the whole flow through pipes with outside diameters of up to 0.5 metres.

PGNAA technology has also been developed for slurry analysis by San Diego-headquartered SABIA, Inc. The company manufactures two types of online analysers. ‘On-belt’ analysers continuously measure the elemental composition of bulk material on a conveyor while ‘onpipe’ analysers are mounted around a slurry pipe to continuously measure the complete slurry stream.

Both types of PGNAA analyser have been installed by major North American phosphate producers and perform full stream, continuous, on-line, multi-elemental analysis. This penetrates the material flow for a completely representative analysis without the need for frequent sampling or multiplexing. This non-intrusive multi-elemental analysis allows operators to simultaneously monitor elements of interest and see percentage composition changes/ trends in essentially real-time.

The technology is uniquely suitable for high throughput (t/h or kg/m 3 volumes) and fast flowing (m/s) bulk materials. SABIA analysers have no moving parts and are easy to install. Their integrated electronics only require two cables – for power and network access.

Many global phosphate producers are considering installing PGNAA to optimise their downstream processing, improve mine grade control, and carry out stockpile blending more expertly. The range of applications includes:

• Run of mine (ROM) bulk sorting
• Stockpile reclaim analysis
• Monitoring of washed phosphate stockpile
• Mine loadout tracking for trains or trucks.

A number of additional applications are also under evaluation:

• Analysis of feed fertilizer and food-grade acids
• Carbonate concentrate/tailings
• Low-grade kiln feed
• Beneficiation recovery
• Flotation final products
• Chlorine/water balance
• Blending/reagent control in flotation cells.

Nuclear magnetic resonance

Massachusetts-headquartered LexMar Global is the world’s leading provider of Nuclear Magnetic Resonance (NMR) analysers for process control. Within the industry, these installations are commonly called Industrial Magnetic Resonance (IMR) systems.

The company has installed more than 400 analysers globally in 45 countries, and operates regional service centres in Belgium, Texas, Morocco, Abu Dhabi, and China. Phosphate industry customers include major players Ma’aden, Mosaic, PotashCorp and OCP, as well as chemical and oil giants such as ExxonMobil, Dow and Borealis. Other markets the company is supplying include polyolefin resin manufacturing and mining.

LexMar Global produces the MagModule II IMR analyser for on-line process measurements on phosphate slurries. These are supplied with either multiplexer or metallurgical sampling systems. The advantages of NMR technology include:

• Direct analysis of phosphate content – as either weight percentage Ca 3 (PO 4 ) 2 (BPL, bone phosphate of lime) or P 2 O 5
• Powders, pellets, slurries and liquids can all be measured
• Non-destructive, rapid analysis with results in less than five minutes
• Stable calibration – no routine re-calibration required
• No sample preparation necessary
• Analysis is independent of particle size
• Robust instrumentation with rugged industrial design and construction
• Avoids use of radioactive materials.

MagModule II on-line phosphate analysers can be installed at different process stages. Units can be placed at the beneficiation stage, to monitor and help regulate froth flotation, further downstream in acid reactor feed control, or upstream in mining operations. The benefits of this include:

• Greater P 2 O 5 recovery with consequently better usage of phosphate rock reserves and less wastage
• Increased plant efficiency and higher production rates
• Lower production costs
• Avoidance of contract penalties.

Coupling the analyser to an automated multiplexer is advantageous as it allows a single analyser to take routine measurement from multiple sample points without interrupting operations.

IMR technology is capable of delivering comparable, consistent results. Analysers are calibrated for P 2 O 5 content by comparing IMR results with laboratory reference measurements over a range of different phosphate compositions. According to LexMar Global, IMR calibrations are intrinsically more stable than those required for alternative techniques such as X-Ray fluorescence (XRF).

One of the main benefits of on-line IMR analysis is that it allows more timely process decisions to be made which, in turn, leads to more consistent product quality. The resulting process improvements can deliver large annual savings and rapid payback.

LexMar Global’s MagModule II IMR analyser

PHOTO: LEXMAR GLOBAL

“Improved process control is the primary benefit of incorporating on-line analysers into your plant,” explains Dr Olaf Kohlmann, LexMar Global’s NMR product manager and strategist. “On-line magnetic resonance will give you phosphate concentration readings within a few minutes. Having real-time information about the process status 24/7 allows the engineers to optimize production for a plant.”

He adds: “Even if you could only improve P 2 O 5 recovery by one single percent, the payback is significant, and the lifespan of your reserve is improved. The amount of material moving through your process decreases. Efficiency, production costs, opex, will all start to go in the right direction.”

IMR analysis of conveyor belt feeds provides continuous real-time information on the grade (BPL) of phosphate rock, enabling precise quality control at the very start of the process. It also helps reduce waste rock.

In froth flotation, IMR analysis again provides real-time BPL data for flotation feeds, concentrates and tailings, improving P 2 O 5 recovery during beneficiation and preventing the over- or under-application of flotation chemicals. When combined with an automatic multiplexer, MagModule II has the ability to sequentially sample from and analyse up to four different process streams.

IMR on-line analysers can also be installed further downstream at the reactor stage in the phosphate production process. Using the technology to monitor feedstock helps optimise reactor control and improves P 2 O 5 recovery and efficiency. Other tangible benefits include reduced production costs and improved product quality and consistency.

The installation of IMR on-line analysers provides rapid payback on investment and delivers long-term profits, according to LexMar Global, even if P 2 O 5 recovery is improved by just a small percentage, due to the operating cost reductions achieved and improved mine life.

The growing need for mining industry automation will open up even greater opportunities for on-line analysis in future, in Dr Kohlmann’s view. “As limited global reserves are expended, but demand increases, innovative process optimisation techniques and refinement efficiencies will become increasingly necessary to compete in the global market,” he concludes.

Laboratory robots

Alsys International has been developing robots, including manufacturing parts and writing software for these, for nearly 30 years, having been founded by the chemical engineer Marc van Beelen in 1992. Marc started developing robotic systems to tackle and overcome the many problems he encountered during his decade-long experience in the laboratory sector. One particular problem – eliminated by the use of robots – is the high margin of human error in extremely accurate measurements.

Alsys currently has four product lines on the market:

• Fertilizer robot
• End-group (oleochemical) robot
• Compact robot l Soil robot.

The main benefits of these robots versus manual analysis are:

• Automated sample preparation
• Integrated analysis techniques
• Reliable analytical results
• Modern data processing
• A safe working environment
• A four-day runtime without the need for an analyst.

Alsys has specialised in building lab robots for the sample preparation and analysis of fertilizer industry raw materials and end products for 20 years. Its fertilizer robot (Alsys RB-247) analyses for phosphorus, potassium, magnesium and other key nutrients/impurities in fertilizers. This fully automated laboratory unit uses Metrohm titrators, Mettler moisture analyser and Metrohm Ion chromatography. Its main functions and operations include:

Alsys laboratory robot.

SOURCE: ALSYS

• Autonomous assessment of solid and liquid samples
• Sample dissolution in water (both cold and boiling) and acid

The unit has the ability to analyse both raw materials and processed samples. Options include:

• Titration and potentiometric determinations
• Moisture analysis
• Ion chromatography
• ICP
• Flow Injection
• Spectrometry.

Alsys robots integrate with enterprise resource planning (ERP) software, SAP and other laboratory information management system (LIMS). With a sample preparation plus analysis time of around eight minutes, they are capable of analysing around 150 samples a day.

The company’s fertilizer industry customers include ICL, ICL Iberia, Iberpotash and Forbon.

“We’ve been working with the lab robot from Alsys International for about 14 years now and are currently running a fully digital production. Samples are taken directly from the mine to the robot for analysis. The data is integrated with LIMS and SAP. We now receive faster, more accurate and digital measurements on ore quality from the mine,” said a laboratory manager at an Israeli mining operation.

The latest development from Alsys is the soil robot. By measuring soil nutrients, this will be able to give fertilization advice based on the analytical results obtained. Currently, the company is looking to offer a robot with the capacity to prep and analyse 1,000 soil samples per day. Soil analysis is a potentially lucrative, large-scale market due to the large difference in unit price between manual and robotic analysis.