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FULLY AUTOMATED SAMPLE PREPARATION AND ANALYSIS IN THE MINING INDUSTRY
FULLY AUTOMATED SAMPLE PREPARATION AND ANALYSIS IN THE MINING INDUSTRY Tina Knudsen Product Manager, FLSmidth Automation, Minerals Industries, Hoeffdingsvej 34, DK-2500 Valby, Denmark
Abstract: Laboratories are constantly faced with demands for improved quality, shorter sample turn around time, improved health and safety condition and better economical results. These laboratories have experienced that by automating one or more of their laboratory procedures, they will gain on all of these demands. One of these laboratories is studied: Reasons for automating, decisions for level of automation and selection of equipment. Special focus is given to dividing of the sample and avoiding contamination from one sample to another. A couple of the equipments included in the system are explained in details and results obtained from these are given. Copyright © 2007 IFAC Keywords: Automation, Automatic operation, Robots, Analysis, Laboratory techniques
1. THE CHALLENGES FOR A MODERN LABORATORY Laboratories all over the world and in all industries are faced with the same kind of challenges: Analytical results must be produced as always, but the cost must constantly be optimised in order to be competitive. The quality of the results must be as reliable as ever, maybe even more reliable since often important decisions are taken based on the results. There may be a requirement for production of an increased number of analytical results per day and/or the analytical results must be produced faster than before. And on top of all this there is an increased focus on providing acceptable working conditions for the lab technicians. In the mining industry, lab services may be undertaken by the mining company itself or the mining company may have chosen to out source these services. However, both the in-house laboratory as well as the commercial laboratory deals with the above mentioned topics. The quality, the economy as well as health and safety issues will be important for both types of laboratories. Thus it is important to study the tools that can assist the laboratories in achieving the required quality, being economical competitive and complying with the health and safety legislation. This paper describes a case study where a mining laboratory for the exact same reasons decided to invest in a fully automatic laboratory.
1.1 Producing analytical results with less ‘cost per sample’ without jeopardizing the quality of the results. The man power is often the heaviest part on the laboratory budget. If a laboratory is able to reduce this cost, it would implicit means that the cost per sample produced can be reduced. Reducing the manning cost would require an operation of the laboratory with fewer personnel. But if the requirement is the same number of samples per day and with the same quality as before, it is not likely that the laboratory manager can lay-off people and still maintain his quality objectives. Maybe he can re-arrange some of the laboratory tasks or in some way organise it differently. This may create smaller savings, but normally considerable savings are not seen as a result of this. More drastic changes must be made. And this would be to introduce automatic operation of the laboratory. Introducing automatic operation should however be done after thorough consideration. It is not an ‘either – or’ discipline. Maybe only one analysis method is feasible to automate, maybe half of what is done in the lab can be automated with economical success or in some cases every main tasks can be automated. Which laboratory procedure it will be feasible to automate will have to be studied in each case. Some procedures are relatively easy to automate, whereas others may require more sophisticated solutions. Looking back at several examples within the industry there are always considerable cost savings involved in automating the crushing and grinding steps of incoming raw materials. Moreover sample preparation
for XRF analysis like pressing sample into steel rings or preparing the samples by fusion, is another area which almost in every case is economical beneficial. A laboratory section with 6-8 laboratory technicians in each shift may typically reduce the manning to at least half, if the main laboratory procedures are automated. In countries with high labour cost or high cost for having personnel employed at a mining site, this reduction in personnel may result in a pay-back time for the automation investment of 2-3 years only. Money is not all. The results also have to be reliable and of the required quality. Once it has been decided to automate a certain work procedure, it is therefore of utmost importance that the automated solutions are selected with care: A) Choose reliable, well proven equipment solutions that can work 24 hours a day, 365 days per year. This must be considered not only for the equipment, but also for the controlling software. B) Choose solutions that follow the correct preparation/analysis procedures according to the required standards. C) Choose flexible solutions which serve not only the needs of today, but also the needs of tomorrow. They must be prepared for extensions with additional equipment, if required later on. 1.2 Improving the sample turn around time. When a laboratory is introducing automatic procedures, it is most often found that things can happen much faster than when a lab technician performs the tasks. No coffee breaks, no lunch and no breaks between the individual operations. An automatic solution works continuously and can be configured to have an optimized sample turnaround time, if so required. In some of the better systems, samples can be prioritised individually. In this way a so-called important sample can be prepared before less important samples. This may especially be interesting in laboratories where production samples are processed. Waiting for a process decision and not being able to take the decision before an analytical result is ready can be expensive. This is extremely important in steel works, but also in many other process areas, considerably saving can be harvested by controlling the process as fast as possible. 1.3 Analytical results independent of the individual skills of the lab personnel. It is not always well received to pin point that the analytical results depends on the person on duty. But more than once this phenomenon has been seen. Some laboratory technicians develop their own kind of procedure or just their own way of doing the work though they follow the procedure as they should. E.g. when an operator is looking for a change of colour as part of a preparation procedure, the results will most likely result in an operator biased result. If the best operator could be on duty during all three shifts, each day, all the year, the results would be of the same high quality – all things equal. But this is of course not possible. But possible it would be to exchange this operator with automatic equipment, which can operate day in and day out with the same high quality. An
automated solution will be able to perform the same procedure in exactly the same way time after time. The better automated solutions have build-in checks at various points in the sample preparation procedure to constantly monitor that everything is done correctly. And it will be able to reject a sample, should it not have been processed according to the foreseen procedures. Completely unmanned laboratories should, however, not be expected. There will always be a need for personnel for supervision and dedicated personnel for conducting daily maintenance. But the amount of personnel will be reduced considerably compared to a manual laboratory executing the same number of samples. It should also be mentioned that though the maintenance personnel does not directly operate the equipment, they have a very important role in an automated laboratory. If the maintenance personnel do not perform their work properly and with the required attention, the equipment will not perform as It was intended to do. The result of this may be as severe as erratic analytical results. 1.4 Improved health and laboratory personnel.
safety condition
for
Automated solutions will remove most of the heavy lifting, the noisy, warm and dusty working environment as well as the monotonous work which can result in unwanted long term health problems for the lab personnel. In some countries the health and safety legislations may be one of the main drivers for introducing automatic operation in the laboratory. In others this may not be the main focus area. However, the trend is that health and safety issues will have an increased impact on the decisions in the laboratories all over the world. 2. AUTOMATION OF A LABORATORY - A CASE STUDY With the above as some of the general considerations anyone who wants to automate have to deal with, this paper will look into the details of a specific solution for automating sample preparation of mainly iron ore. The solution is fully automated; i.e. it requires no lab personnel during operating hours, instead a robot is handling the samples. The solution consist of a standard robot cell for crushing and grinding of incoming samples, dosing of back-up samples into vials, barcode labelling, fusion of beads including correct weighing of sample and flux, LOI determination and XRF analysis. The layout of the entire system can be seen in figure 1.
After a study of the present manning, the cost of manning, the operating hours and the future requirement for a decreased cost per sample, it was found that the best solution would be to automate all steps except the drying step. Automation of drying is possible and done in some cases, but the handling of trays and material is relatively expensive compared to manual operation.
Fig. 1. Lay-out of the automatic systems: One robot cell (MSP2) for coarse sample preparation, two robot cells (ADFX4) for fused bead preparation, one robot cell interconnecting these three robot cells and feeding samples to the back-up sample dosing equipment (SDU). Plus one automatic cell for loss-on-ignition determination (LOI). 2.1 The design criteria The design of the system evolved during a series of dialogs between the supplier and the customer. The customer had the following requirements: A) The automated lab must be able to prepare 36 iron ore samples per hour for XRF analysis, B) the cost per sample shall be decreased (for confidentiality reasons the exact price level cannot be revealed) compared to the price for manual preparation, C) the sample preparation procedures shall follow the required standards and D) weight of in-coming samples between 0,5 to 10 kg, particle size up to 100 mm and predominantly iron ores, but other ores may be treated as well. In addition to these specific objectives, the customer wanted the system to ensure a low degree of operator errors. Preparing samples for XRF analysis involves several steps. These steps can be seen in figure 2.
Fig. 2. Steps involved in sample preparation for XRF analysis. Now the basic steps were identified. But more functionality should be added to the system. The customer would also like to have a possibility to prepare back-up samples, to prepare samples for other analysis methods than XRF and to be able to introduce QC samples when required. Not all incoming samples would have the same particle size. Hence it should be possible to skip the crushing step in those situations, where the samples could go directly to the grinding step.
The rest of the design of the system was now merely a matter of selecting the right type of equipment and selecting the amount of equipment that would be required in order to ensure the 36 samples per hour. 2.2 Selection of equipment The in-coming samples may be up to 10 kg samples. The particle size will typically be 20 mm, however in some cases even more – up to 100 mm. The amount required for XRF analysis is around 1 gram of fused sample. To ensure sample representativity in the final steps, it is obvious that special case must be taken when dividing the samples. This has therefore been one of the focus areas when selecting the equipment. Another has been to ensure a contamination-free sample. Running an automatic system with 36 samples per hour and no operator intervention inbetween each samples, requires that the system has been designed with as few points of potential contamination as possible. And that for each of these potential contamination points, the build-in cleaning features must be of a very high standard. Dividing of the sample and ensuring a contaminationfree environment will be dealt with in the following chapters, by detailed explanation of some of the equipment included in the system. Before then, a short description of all the included equipment will be given. Automation and Control Software. Firstly it can be mentioned that all samples entering the system or leaving the system will be registered in the over-all control software, called the QCX software. (QCX stands for Quality Control of X, with X being all quality related issues). The samples are constantly traced, and at any point in time, it will be possible to see where a sample and its related sub-samples are and which kind of preparation or analysis they are undergoing at that point in time. Plus of course, what they have been through and what still needs to be done. In addition to this the sample identification data, which are born the LIMS of the customer, will be transferred directly to the QCX software. In this way operator typing errors are eliminated. However, should a situation occur where there is a need for an operator to manually enter sample id into the QCX software, this can of course also be done. And he/she can scan barcodes attached to incoming samples should this be required. It must also be mentioned that barcodes are automatically attached to the back-up samples leaving the system. Coarse Preparation Cell. The equipment chosen for crushing and splitting is a combined version and for
capacity reasons a dual version of this crusher/splitter has been chosen. There are 6 grinding mills used in the system. The mills are of the type that has a removable bowl and puck. The bowl and puck are cleaned in one of two cleaning stations. All of this above mentioned equipment is handled in one robot cell, called the MSP2 cell. Loss-on-Ignition. Loss-on ignition is determined in a series of 4 furnaces. Batches of 40 samples are handled at a time. This equipment is handled by a linear manipulator. Fusions Cells. The equipment for fusion consists of two identical robot cells, the ADFX4 cells. Each of the cells consists of a dosing unit, which doses sample and flux, and cleans the platinum crucibles. Plus four furnaces and a casting carousel. The casting carousel has positions for pre-heating of the mould, casting, cooling of the mould and pick-up of the fused bead. From the ADFX4 cells the fused beads travels on conveyor belts to the XRF, which in this case is a simultaneous wavelength dispersive type. Sample Distributing Cell. In between the MSP2 cell, the ADFX4 cells and the LOI cell there is a sample distributing cell, called the IHUB cell. The IHUB cell also doses samples for back-up purposes, cleans sample containers and has storage locations for empty and filled containers. 2.3 Dividing of the samples Dividing a sample into one or more sub-samples is actually the same as what is commonly known as sampling. By sampling one takes out a smaller part (one or more increments) of the lot. Theory of Sampling. In an automatic system like the one explained here, the sample has to be divided for two reasons: To minimize the sample portion to the required size for onwards processing or to split the sample into two or more sub-samples each of which will have its own onwards processing. In both situations we can use the Theory of Sampling (TOS) to guide us in selection of the dividing method. First it should be understood, why it is important to divide correctly, or to divide with as small a selection error as possible. The selection error, SE, can be expressed as
SE =
aS − aL aL
where aS = mass of analyte in the sample/total sample mass
a L = mass of analyte in lot/total mass lot mass The objective will therefore be to ensure that
aS
equals a L , or at least gets as close as possible. If the lot is iron ore and the analyte is Fe, the selection error
is important, but not as critical as the situation where the lot is a gold bearing ore and the analyte is Au, simply because of the analyte level. Still thorough consideration must be taken when dividing also in the case of iron ore. Some may claim that the sample (lot) to be divided has been homogenized and that a sample from the lot can be taken easily. However, this is never true. The selection error – which is actually the Fundamental Sampling Error, FSE, can only be strictly zero if A) the sample is the whole lot and B) the lot is strictly homogeneous. And since no lot is truly homogeneous and we have to divide the lot (= in-coming samples), we have to treat the in-coming samples carefully in order to minimize the FSE. Basically one would have to make use of Gy’s formula to estimate FSE and then find the necessary sample mass and the corresponding particle size. In practise this cannot be done in each situation and for each material. Instead the basic TOS principles, previous results and experiences from similar materials are used as equipment and method selection tool. Without going into details, the dividing of the lot should take place while transforming it from a zerodimensional lot to a one-dimensional lot. This means dividing while moving the lot. This can be done in several ways, where experiments (Petersen and Espensen, 2004) have shown that the use of riffle splitters or rotating dividers give the best representativity in the sample. In an automatic system the use of riffle splitters is not feasible, but rotary dividers are. Hence this type of divider has been installed after the crusher in the discussed system. The crusher reduces the particle size to – 3mm, the rotary divider splits the crushed sample into a 1 kg subsample. The divider can be adjusted to give a smaller or bigger split depending of the in-coming sample weight. Sample Dosing Unit. One of the other equipments for divisions of samples in the system is Sample Dosing Unit, SDU800. This unit, please see Fig.3, is gravimetrically dosing samples for back-up purposes into vials. Choosing a gravimetric dosing principle in this case ensures a precise dosing and moreover a high degree of flexibility for choosing number of vials to be dosed. The typical target weight for each vial is 100 gram with +/- 10% accuracy for material with a particle size -150 µm. However, the required accuracy can be changed, if so required. The dosing can be more precise, but slower or it can be faster, but less precise. The working principle of this unit is the following: A cup containing 600 cc is placed by the robot at an input cup position. Hereafter the SDU800 handles the dosing internally in the unit. From the cup the sample is automatically dosed gravimetrically into a vial. The vial is then closed by a lid and then transported out on an out-going conveyor on the operator side of the unit. A barcode label is automatically attached to the vial, where after the vial is stored. After dosing into the first vial, the SDU may continue dosing into more vials and/or it may dose a sample portion into a
smaller cup for onwards processing in the automatic system.
smooth and even allowing the sample material to flow freely. Some equipment may have to be cleaned by compressed air, others by water, others again by acid or any combination hereof. Finally the sample material it self should be dry and non-sticky if at all possible. Two pieces of equipment which has been designed with special focus on securing a contamination-free sample will be discussed below: Large Grinding Mill. The first equipment is the grinding mill, the LM2. Please see figure 4, where the MSP cell containing 6 of these mills are shown.
Fig. 3. Sample Dosing Unit, SDU800, for dosing of back-up samples into vials. This type of dividing of a sample can be relevant only where the sample to be dosed is fairly homogeneous in respect of particle size distribution and density. And where the particle size is -150 µm. But if these criteria are fulfilled, the FSE will be low – or in other words, the representativity of the dividing will be acceptable for most common purposes. The two dividing principle mentioned above – the use of a rotary divider and the use of a gravimetric dosing principle – are the two main dividing principles in the automated system explained here. The discussions above shows, that when designing automatic systems, several parameters have to be taken into consideration before a given solution can be found: The material properties, the requirement for representativity, the theory, the practical implementation and of course also the economical aspect. 2.4 Contamination-free samples As previously mentioned it is important to ensure that the automatic system has focus on bringing the contamination between samples to an absolute minimum. One can imagine the possibilities of leaving a little bit of sample somewhere in the equipment and thereby polluting the next sample. If this happens, it is of course not so critical if 10 gram of sample is left in the crusher and polluting the next 10 kg sample with these 10 gram. This will give 0.1% pollution of the whole sample, which in many situations will be acceptable. Are we in the smaller sample sizes like when dosing for fusion, even small parts of sample left over, can be very critical. Should just half a gram be left over from one sample to another when dosing for fused bead preparation, the pollution may be up to 50%, which of course is unacceptable. But both for coarse as well as fine sample material, it is important that the equipment chosen is designed with this in mind: Dust generation must be kept at a minimum. When dust is produced where it is unavoidable, it must be extracted. Surfaces must be
Fig. 4. The MSP2 cell where 6 LM2 mills are seen. The LM2 is a swing mill capable of grinding up to 1.8 kg of material with a particle size up to 20 mm. The grinding time depends on the material type, but will typically be around 4 to 5 minutes to reach -75 µm. Traditional grinding mills for automatic use cannot remove the grinding bowl like an operator would be used to do when preparing samples. Instead the bowl and puck will be cleaned while inside the mill. This requires special care to ensure that all material is emptied out of the bowl and that the bowl is later cleaned properly. Ensuring this would normally mean that a pre-grinding must be made. (This is also referred to as blind grinding). A pre-grinding costs sample material, it takes time and contamination may still occur. The LM2 mills shown in figure 4 and which are part of the MSP cell discussed in this chapter is designed for removal of the grinding bowl and puck by robot. The bowl and puck are cleaned in a dedicated cleaning station by use of blast cleaning. Transport to and from is handled by the robot. This procedure ensures that any sample material that may adhere to the surfaces of the bowl and/or puck or any loose material that has not been removed completely while emptying the bowl is now completely removed before the next sample is introduced. Please see fig. 5. Sample and Flux Dosing Unit. The other, but quite different piece of equipment, that will be treated here is a unit called DCF800, Dosing Cleaning Flux unit. This unit doses sample and flux into a platinum crucible. The unit also cleans the used crucibles. Please refer to fig.6. The design criteria for this unit has been to achieve a very accurate, contamination free dosing of flux and sample. The basic idea of this unit is therefore that it shall dose the sample material directly from the in-coming sample container, in this
case a 100 cc cup. The robot places the cup at an input position and the dosing of sample and flux is then handled internally in the unit after the sample principle as in the SDU800 unit. The cup is tilted a certain degree, rotated in two direction whereby the sample is dosed from the cup into the platinum crucible. This means that the sample material is not in contact with anything in this unit and contamination cannot occur.
operator will be able to perform as accurate as these results show. And in practise he will not be able to perform at such a high level throughout an 8 hour working day. 3. CONCLUSION Automation of a mining laboratory can be a cost efficient way of sample preparation and analyses. Manning cost can easily be cut by 50%, quality can be optimized, and health and safety issues can be improved for the laboratory personnel. One or more robotic cells with dedicated equipment designed with the correct theory, the relevant standards, sample physics and a practical approach in mind will solve the most common requirements in the mining laboratories. Table 1.Accuracy of dosing sample and flux in the DCF800.
Sample [g]
Flux [g]
Total weight (smp+ flux) SMP:Flux [g]
1
1.5095
7.5482
0.2000
9.0577
0.1666
2
1.4971
7.4858
0.2000
8.9829
0.1666
3
1.4951
7.4755
0.2000
8.9706
0.1666
4
1.4979
7.4897
0.2000
8.9876
0.1666
5
1.4992
7.4963
0.2000
8.9955
0.1666
6
1.4964
7.4827
0.2000
8.9791
0.1666
7
1.5050
7.5250
0.2000
9.0300
0.1666
8
1.5101
7.5503
0.2000
9.0604
0.1666
9
1.5044
7.5230
0.2000
9.0274
0.1666
10
1.5033
7.5166
0.2000
9.0199
0.1666
11
1.5036
7.5191
0.2000
9.0227
0.1666
12
1.5011
7.5056
0.2000
9.0067
0.1666
13
1.5067
7.5338
0.2000
9.0405
0.1666
14
1.5099
7.5496
0.2000
9.0595
0.1666
15
1.5030
7.5149
0.2000
9.0179
0.1666
16
1.5138
7.5666
0.2001
9.0804
0.1667
17
1.5036
7.5180
0.2000
9.0216
0.1666
18
1.5178
7.5896
0.2000
9.1074
0.1666
19
1.5281
7.6404
0.2000
9.1685
0.1666
20
1.5003
7.5019
0.2000
9.0022
0.1666
21
1.4973
7.4863
0.2000
8.9836
0.1666
Avera ge
1.5049
7.5247
0.2000
9.0296
0.1666
Min
1.4951
7.4755
0.2000
8.9706
0.1666
Max
1.5281
7.6404
0.2001
9.1685
0.1667
St.dev
0.0080
0.0397
0.0000
0.0477
0.0000
Fig. 5. Grinding bowl and puck.
Fig. 6. DCF800 unit for dosing of sample and flux plus cleaning of platinum crucible. The flux is dosed from a container through a vibrating chute into the platinum crucible. Here the risk of contamination is not high either, since the flux is the same type for all samples. Dosing takes place in an upper compartment of the unit. In a lower compartment used crucibles are cleaned first in an ultrasonic acid bath, then in a water bath and finally the crucibles are dried. This unit has been used several years in automatic production labs where a high number of fused beads are made every hour. And contamination problems while dosing in this unit has never been experienced. 2.5 Improved quality The DCF800 dosing unit is an example of a piece of equipment where the automatic solution is better than the average operator. Table 1 shows results from a series of test of dosing accuracy. Only a top notch
Dilution ratio Smp/(Tot flux+Smp)
REFERENCES Petersen, L., Esbensen, K. (2004) Representative Sampling for Reliable Data Analyses: TOS (Theory of Sampling). Journal of Chemometrics
Abstract: Laboratories are constantly faced with demands for improved quality, shorter sample turn around time, improved health and safety condition and better economical results. These laboratories have experienced that by automating one or more of their laboratory procedures, they will gain on all of these demands. One of these laboratories is studied: Reasons for automating, decisions for level of automation and selection of equipment. Special focus is given to dividing of the sample and avoiding contamination from one sample to another. A couple of the equipments included in the system are explained in details and results obtained from these are given. Copyright © 2007 IFAC Keywords: Automation, Automatic operation, Robots, Analysis, Laboratory techniques
1. THE CHALLENGES FOR A MODERN LABORATORY Laboratories all over the world and in all industries are faced with the same kind of challenges: Analytical results must be produced as always, but the cost must constantly be optimised in order to be competitive. The quality of the results must be as reliable as ever, maybe even more reliable since often important decisions are taken based on the results. There may be a requirement for production of an increased number of analytical results per day and/or the analytical results must be produced faster than before. And on top of all this there is an increased focus on providing acceptable working conditions for the lab technicians. In the mining industry, lab services may be undertaken by the mining company itself or the mining company may have chosen to out source these services. However, both the in-house laboratory as well as the commercial laboratory deals with the above mentioned topics. The quality, the economy as well as health and safety issues will be important for both types of laboratories. Thus it is important to study the tools that can assist the laboratories in achieving the required quality, being economical competitive and complying with the health and safety legislation. This paper describes a case study where a mining laboratory for the exact same reasons decided to invest in a fully automatic laboratory.
1.1 Producing analytical results with less ‘cost per sample’ without jeopardizing the quality of the results. The man power is often the heaviest part on the laboratory budget. If a laboratory is able to reduce this cost, it would implicit means that the cost per sample produced can be reduced. Reducing the manning cost would require an operation of the laboratory with fewer personnel. But if the requirement is the same number of samples per day and with the same quality as before, it is not likely that the laboratory manager can lay-off people and still maintain his quality objectives. Maybe he can re-arrange some of the laboratory tasks or in some way organise it differently. This may create smaller savings, but normally considerable savings are not seen as a result of this. More drastic changes must be made. And this would be to introduce automatic operation of the laboratory. Introducing automatic operation should however be done after thorough consideration. It is not an ‘either – or’ discipline. Maybe only one analysis method is feasible to automate, maybe half of what is done in the lab can be automated with economical success or in some cases every main tasks can be automated. Which laboratory procedure it will be feasible to automate will have to be studied in each case. Some procedures are relatively easy to automate, whereas others may require more sophisticated solutions. Looking back at several examples within the industry there are always considerable cost savings involved in automating the crushing and grinding steps of incoming raw materials. Moreover sample preparation
for XRF analysis like pressing sample into steel rings or preparing the samples by fusion, is another area which almost in every case is economical beneficial. A laboratory section with 6-8 laboratory technicians in each shift may typically reduce the manning to at least half, if the main laboratory procedures are automated. In countries with high labour cost or high cost for having personnel employed at a mining site, this reduction in personnel may result in a pay-back time for the automation investment of 2-3 years only. Money is not all. The results also have to be reliable and of the required quality. Once it has been decided to automate a certain work procedure, it is therefore of utmost importance that the automated solutions are selected with care: A) Choose reliable, well proven equipment solutions that can work 24 hours a day, 365 days per year. This must be considered not only for the equipment, but also for the controlling software. B) Choose solutions that follow the correct preparation/analysis procedures according to the required standards. C) Choose flexible solutions which serve not only the needs of today, but also the needs of tomorrow. They must be prepared for extensions with additional equipment, if required later on. 1.2 Improving the sample turn around time. When a laboratory is introducing automatic procedures, it is most often found that things can happen much faster than when a lab technician performs the tasks. No coffee breaks, no lunch and no breaks between the individual operations. An automatic solution works continuously and can be configured to have an optimized sample turnaround time, if so required. In some of the better systems, samples can be prioritised individually. In this way a so-called important sample can be prepared before less important samples. This may especially be interesting in laboratories where production samples are processed. Waiting for a process decision and not being able to take the decision before an analytical result is ready can be expensive. This is extremely important in steel works, but also in many other process areas, considerably saving can be harvested by controlling the process as fast as possible. 1.3 Analytical results independent of the individual skills of the lab personnel. It is not always well received to pin point that the analytical results depends on the person on duty. But more than once this phenomenon has been seen. Some laboratory technicians develop their own kind of procedure or just their own way of doing the work though they follow the procedure as they should. E.g. when an operator is looking for a change of colour as part of a preparation procedure, the results will most likely result in an operator biased result. If the best operator could be on duty during all three shifts, each day, all the year, the results would be of the same high quality – all things equal. But this is of course not possible. But possible it would be to exchange this operator with automatic equipment, which can operate day in and day out with the same high quality. An
automated solution will be able to perform the same procedure in exactly the same way time after time. The better automated solutions have build-in checks at various points in the sample preparation procedure to constantly monitor that everything is done correctly. And it will be able to reject a sample, should it not have been processed according to the foreseen procedures. Completely unmanned laboratories should, however, not be expected. There will always be a need for personnel for supervision and dedicated personnel for conducting daily maintenance. But the amount of personnel will be reduced considerably compared to a manual laboratory executing the same number of samples. It should also be mentioned that though the maintenance personnel does not directly operate the equipment, they have a very important role in an automated laboratory. If the maintenance personnel do not perform their work properly and with the required attention, the equipment will not perform as It was intended to do. The result of this may be as severe as erratic analytical results. 1.4 Improved health and laboratory personnel.
safety condition
for
Automated solutions will remove most of the heavy lifting, the noisy, warm and dusty working environment as well as the monotonous work which can result in unwanted long term health problems for the lab personnel. In some countries the health and safety legislations may be one of the main drivers for introducing automatic operation in the laboratory. In others this may not be the main focus area. However, the trend is that health and safety issues will have an increased impact on the decisions in the laboratories all over the world. 2. AUTOMATION OF A LABORATORY - A CASE STUDY With the above as some of the general considerations anyone who wants to automate have to deal with, this paper will look into the details of a specific solution for automating sample preparation of mainly iron ore. The solution is fully automated; i.e. it requires no lab personnel during operating hours, instead a robot is handling the samples. The solution consist of a standard robot cell for crushing and grinding of incoming samples, dosing of back-up samples into vials, barcode labelling, fusion of beads including correct weighing of sample and flux, LOI determination and XRF analysis. The layout of the entire system can be seen in figure 1.
After a study of the present manning, the cost of manning, the operating hours and the future requirement for a decreased cost per sample, it was found that the best solution would be to automate all steps except the drying step. Automation of drying is possible and done in some cases, but the handling of trays and material is relatively expensive compared to manual operation.
Fig. 1. Lay-out of the automatic systems: One robot cell (MSP2) for coarse sample preparation, two robot cells (ADFX4) for fused bead preparation, one robot cell interconnecting these three robot cells and feeding samples to the back-up sample dosing equipment (SDU). Plus one automatic cell for loss-on-ignition determination (LOI). 2.1 The design criteria The design of the system evolved during a series of dialogs between the supplier and the customer. The customer had the following requirements: A) The automated lab must be able to prepare 36 iron ore samples per hour for XRF analysis, B) the cost per sample shall be decreased (for confidentiality reasons the exact price level cannot be revealed) compared to the price for manual preparation, C) the sample preparation procedures shall follow the required standards and D) weight of in-coming samples between 0,5 to 10 kg, particle size up to 100 mm and predominantly iron ores, but other ores may be treated as well. In addition to these specific objectives, the customer wanted the system to ensure a low degree of operator errors. Preparing samples for XRF analysis involves several steps. These steps can be seen in figure 2.
Fig. 2. Steps involved in sample preparation for XRF analysis. Now the basic steps were identified. But more functionality should be added to the system. The customer would also like to have a possibility to prepare back-up samples, to prepare samples for other analysis methods than XRF and to be able to introduce QC samples when required. Not all incoming samples would have the same particle size. Hence it should be possible to skip the crushing step in those situations, where the samples could go directly to the grinding step.
The rest of the design of the system was now merely a matter of selecting the right type of equipment and selecting the amount of equipment that would be required in order to ensure the 36 samples per hour. 2.2 Selection of equipment The in-coming samples may be up to 10 kg samples. The particle size will typically be 20 mm, however in some cases even more – up to 100 mm. The amount required for XRF analysis is around 1 gram of fused sample. To ensure sample representativity in the final steps, it is obvious that special case must be taken when dividing the samples. This has therefore been one of the focus areas when selecting the equipment. Another has been to ensure a contamination-free sample. Running an automatic system with 36 samples per hour and no operator intervention inbetween each samples, requires that the system has been designed with as few points of potential contamination as possible. And that for each of these potential contamination points, the build-in cleaning features must be of a very high standard. Dividing of the sample and ensuring a contaminationfree environment will be dealt with in the following chapters, by detailed explanation of some of the equipment included in the system. Before then, a short description of all the included equipment will be given. Automation and Control Software. Firstly it can be mentioned that all samples entering the system or leaving the system will be registered in the over-all control software, called the QCX software. (QCX stands for Quality Control of X, with X being all quality related issues). The samples are constantly traced, and at any point in time, it will be possible to see where a sample and its related sub-samples are and which kind of preparation or analysis they are undergoing at that point in time. Plus of course, what they have been through and what still needs to be done. In addition to this the sample identification data, which are born the LIMS of the customer, will be transferred directly to the QCX software. In this way operator typing errors are eliminated. However, should a situation occur where there is a need for an operator to manually enter sample id into the QCX software, this can of course also be done. And he/she can scan barcodes attached to incoming samples should this be required. It must also be mentioned that barcodes are automatically attached to the back-up samples leaving the system. Coarse Preparation Cell. The equipment chosen for crushing and splitting is a combined version and for
capacity reasons a dual version of this crusher/splitter has been chosen. There are 6 grinding mills used in the system. The mills are of the type that has a removable bowl and puck. The bowl and puck are cleaned in one of two cleaning stations. All of this above mentioned equipment is handled in one robot cell, called the MSP2 cell. Loss-on-Ignition. Loss-on ignition is determined in a series of 4 furnaces. Batches of 40 samples are handled at a time. This equipment is handled by a linear manipulator. Fusions Cells. The equipment for fusion consists of two identical robot cells, the ADFX4 cells. Each of the cells consists of a dosing unit, which doses sample and flux, and cleans the platinum crucibles. Plus four furnaces and a casting carousel. The casting carousel has positions for pre-heating of the mould, casting, cooling of the mould and pick-up of the fused bead. From the ADFX4 cells the fused beads travels on conveyor belts to the XRF, which in this case is a simultaneous wavelength dispersive type. Sample Distributing Cell. In between the MSP2 cell, the ADFX4 cells and the LOI cell there is a sample distributing cell, called the IHUB cell. The IHUB cell also doses samples for back-up purposes, cleans sample containers and has storage locations for empty and filled containers. 2.3 Dividing of the samples Dividing a sample into one or more sub-samples is actually the same as what is commonly known as sampling. By sampling one takes out a smaller part (one or more increments) of the lot. Theory of Sampling. In an automatic system like the one explained here, the sample has to be divided for two reasons: To minimize the sample portion to the required size for onwards processing or to split the sample into two or more sub-samples each of which will have its own onwards processing. In both situations we can use the Theory of Sampling (TOS) to guide us in selection of the dividing method. First it should be understood, why it is important to divide correctly, or to divide with as small a selection error as possible. The selection error, SE, can be expressed as
SE =
aS − aL aL
where aS = mass of analyte in the sample/total sample mass
a L = mass of analyte in lot/total mass lot mass The objective will therefore be to ensure that
aS
equals a L , or at least gets as close as possible. If the lot is iron ore and the analyte is Fe, the selection error
is important, but not as critical as the situation where the lot is a gold bearing ore and the analyte is Au, simply because of the analyte level. Still thorough consideration must be taken when dividing also in the case of iron ore. Some may claim that the sample (lot) to be divided has been homogenized and that a sample from the lot can be taken easily. However, this is never true. The selection error – which is actually the Fundamental Sampling Error, FSE, can only be strictly zero if A) the sample is the whole lot and B) the lot is strictly homogeneous. And since no lot is truly homogeneous and we have to divide the lot (= in-coming samples), we have to treat the in-coming samples carefully in order to minimize the FSE. Basically one would have to make use of Gy’s formula to estimate FSE and then find the necessary sample mass and the corresponding particle size. In practise this cannot be done in each situation and for each material. Instead the basic TOS principles, previous results and experiences from similar materials are used as equipment and method selection tool. Without going into details, the dividing of the lot should take place while transforming it from a zerodimensional lot to a one-dimensional lot. This means dividing while moving the lot. This can be done in several ways, where experiments (Petersen and Espensen, 2004) have shown that the use of riffle splitters or rotating dividers give the best representativity in the sample. In an automatic system the use of riffle splitters is not feasible, but rotary dividers are. Hence this type of divider has been installed after the crusher in the discussed system. The crusher reduces the particle size to – 3mm, the rotary divider splits the crushed sample into a 1 kg subsample. The divider can be adjusted to give a smaller or bigger split depending of the in-coming sample weight. Sample Dosing Unit. One of the other equipments for divisions of samples in the system is Sample Dosing Unit, SDU800. This unit, please see Fig.3, is gravimetrically dosing samples for back-up purposes into vials. Choosing a gravimetric dosing principle in this case ensures a precise dosing and moreover a high degree of flexibility for choosing number of vials to be dosed. The typical target weight for each vial is 100 gram with +/- 10% accuracy for material with a particle size -150 µm. However, the required accuracy can be changed, if so required. The dosing can be more precise, but slower or it can be faster, but less precise. The working principle of this unit is the following: A cup containing 600 cc is placed by the robot at an input cup position. Hereafter the SDU800 handles the dosing internally in the unit. From the cup the sample is automatically dosed gravimetrically into a vial. The vial is then closed by a lid and then transported out on an out-going conveyor on the operator side of the unit. A barcode label is automatically attached to the vial, where after the vial is stored. After dosing into the first vial, the SDU may continue dosing into more vials and/or it may dose a sample portion into a
smaller cup for onwards processing in the automatic system.
smooth and even allowing the sample material to flow freely. Some equipment may have to be cleaned by compressed air, others by water, others again by acid or any combination hereof. Finally the sample material it self should be dry and non-sticky if at all possible. Two pieces of equipment which has been designed with special focus on securing a contamination-free sample will be discussed below: Large Grinding Mill. The first equipment is the grinding mill, the LM2. Please see figure 4, where the MSP cell containing 6 of these mills are shown.
Fig. 3. Sample Dosing Unit, SDU800, for dosing of back-up samples into vials. This type of dividing of a sample can be relevant only where the sample to be dosed is fairly homogeneous in respect of particle size distribution and density. And where the particle size is -150 µm. But if these criteria are fulfilled, the FSE will be low – or in other words, the representativity of the dividing will be acceptable for most common purposes. The two dividing principle mentioned above – the use of a rotary divider and the use of a gravimetric dosing principle – are the two main dividing principles in the automated system explained here. The discussions above shows, that when designing automatic systems, several parameters have to be taken into consideration before a given solution can be found: The material properties, the requirement for representativity, the theory, the practical implementation and of course also the economical aspect. 2.4 Contamination-free samples As previously mentioned it is important to ensure that the automatic system has focus on bringing the contamination between samples to an absolute minimum. One can imagine the possibilities of leaving a little bit of sample somewhere in the equipment and thereby polluting the next sample. If this happens, it is of course not so critical if 10 gram of sample is left in the crusher and polluting the next 10 kg sample with these 10 gram. This will give 0.1% pollution of the whole sample, which in many situations will be acceptable. Are we in the smaller sample sizes like when dosing for fusion, even small parts of sample left over, can be very critical. Should just half a gram be left over from one sample to another when dosing for fused bead preparation, the pollution may be up to 50%, which of course is unacceptable. But both for coarse as well as fine sample material, it is important that the equipment chosen is designed with this in mind: Dust generation must be kept at a minimum. When dust is produced where it is unavoidable, it must be extracted. Surfaces must be
Fig. 4. The MSP2 cell where 6 LM2 mills are seen. The LM2 is a swing mill capable of grinding up to 1.8 kg of material with a particle size up to 20 mm. The grinding time depends on the material type, but will typically be around 4 to 5 minutes to reach -75 µm. Traditional grinding mills for automatic use cannot remove the grinding bowl like an operator would be used to do when preparing samples. Instead the bowl and puck will be cleaned while inside the mill. This requires special care to ensure that all material is emptied out of the bowl and that the bowl is later cleaned properly. Ensuring this would normally mean that a pre-grinding must be made. (This is also referred to as blind grinding). A pre-grinding costs sample material, it takes time and contamination may still occur. The LM2 mills shown in figure 4 and which are part of the MSP cell discussed in this chapter is designed for removal of the grinding bowl and puck by robot. The bowl and puck are cleaned in a dedicated cleaning station by use of blast cleaning. Transport to and from is handled by the robot. This procedure ensures that any sample material that may adhere to the surfaces of the bowl and/or puck or any loose material that has not been removed completely while emptying the bowl is now completely removed before the next sample is introduced. Please see fig. 5. Sample and Flux Dosing Unit. The other, but quite different piece of equipment, that will be treated here is a unit called DCF800, Dosing Cleaning Flux unit. This unit doses sample and flux into a platinum crucible. The unit also cleans the used crucibles. Please refer to fig.6. The design criteria for this unit has been to achieve a very accurate, contamination free dosing of flux and sample. The basic idea of this unit is therefore that it shall dose the sample material directly from the in-coming sample container, in this
case a 100 cc cup. The robot places the cup at an input position and the dosing of sample and flux is then handled internally in the unit after the sample principle as in the SDU800 unit. The cup is tilted a certain degree, rotated in two direction whereby the sample is dosed from the cup into the platinum crucible. This means that the sample material is not in contact with anything in this unit and contamination cannot occur.
operator will be able to perform as accurate as these results show. And in practise he will not be able to perform at such a high level throughout an 8 hour working day. 3. CONCLUSION Automation of a mining laboratory can be a cost efficient way of sample preparation and analyses. Manning cost can easily be cut by 50%, quality can be optimized, and health and safety issues can be improved for the laboratory personnel. One or more robotic cells with dedicated equipment designed with the correct theory, the relevant standards, sample physics and a practical approach in mind will solve the most common requirements in the mining laboratories. Table 1.Accuracy of dosing sample and flux in the DCF800.
Sample [g]
Flux [g]
Total weight (smp+ flux) SMP:Flux [g]
1
1.5095
7.5482
0.2000
9.0577
0.1666
2
1.4971
7.4858
0.2000
8.9829
0.1666
3
1.4951
7.4755
0.2000
8.9706
0.1666
4
1.4979
7.4897
0.2000
8.9876
0.1666
5
1.4992
7.4963
0.2000
8.9955
0.1666
6
1.4964
7.4827
0.2000
8.9791
0.1666
7
1.5050
7.5250
0.2000
9.0300
0.1666
8
1.5101
7.5503
0.2000
9.0604
0.1666
9
1.5044
7.5230
0.2000
9.0274
0.1666
10
1.5033
7.5166
0.2000
9.0199
0.1666
11
1.5036
7.5191
0.2000
9.0227
0.1666
12
1.5011
7.5056
0.2000
9.0067
0.1666
13
1.5067
7.5338
0.2000
9.0405
0.1666
14
1.5099
7.5496
0.2000
9.0595
0.1666
15
1.5030
7.5149
0.2000
9.0179
0.1666
16
1.5138
7.5666
0.2001
9.0804
0.1667
17
1.5036
7.5180
0.2000
9.0216
0.1666
18
1.5178
7.5896
0.2000
9.1074
0.1666
19
1.5281
7.6404
0.2000
9.1685
0.1666
20
1.5003
7.5019
0.2000
9.0022
0.1666
21
1.4973
7.4863
0.2000
8.9836
0.1666
Avera ge
1.5049
7.5247
0.2000
9.0296
0.1666
Min
1.4951
7.4755
0.2000
8.9706
0.1666
Max
1.5281
7.6404
0.2001
9.1685
0.1667
St.dev
0.0080
0.0397
0.0000
0.0477
0.0000
Fig. 5. Grinding bowl and puck.
Fig. 6. DCF800 unit for dosing of sample and flux plus cleaning of platinum crucible. The flux is dosed from a container through a vibrating chute into the platinum crucible. Here the risk of contamination is not high either, since the flux is the same type for all samples. Dosing takes place in an upper compartment of the unit. In a lower compartment used crucibles are cleaned first in an ultrasonic acid bath, then in a water bath and finally the crucibles are dried. This unit has been used several years in automatic production labs where a high number of fused beads are made every hour. And contamination problems while dosing in this unit has never been experienced. 2.5 Improved quality The DCF800 dosing unit is an example of a piece of equipment where the automatic solution is better than the average operator. Table 1 shows results from a series of test of dosing accuracy. Only a top notch
Dilution ratio Smp/(Tot flux+Smp)
REFERENCES Petersen, L., Esbensen, K. (2004) Representative Sampling for Reliable Data Analyses: TOS (Theory of Sampling). Journal of Chemometrics