Ore Sample Data Delivered Online in Real-time
The traditional technique of taking ore and material samples to the laboratory for testing is misaligned with the reality in the present atmosphere. The accent is on cost containment, improving efficiency, enhancing costs and reducing environmental footprint. It has been observed that mining and mineral processing companies are adopting on-line analysis as an alternative, with X-ray Fluorescence as one of the techniques.Â
Worldwide, conspicuously, in most mines ore grade has been dropping. Highly valuable deposits in shallow areas, which were easier to mine, have been depleted. As a result, surface mines are going underground, and underground mines, ultra-deep. Usually, mining in these areas comes at a colossal cost – increasing operating expenses, on top of safety and environmental risks. This is reflected on the balance sheet.
Yet, despite this challenge, as businesses, mining companies have to remain profitable and compliant. A tried and tested approach at the disposal of mining companies is adopting techniques that can ensure that their operations are cost-effective, profitable, safe, and environmentally friendly. Among a host of means worth exploiting is the early sorting of materials or ore in the mining and mineral processing chain to eliminate waste rock and improve ore grade, which optimises mineral recovery. Most importantly, in this way, wastage of resources such as chemicals, water, and energy used on crushing and screening is reduced (crushing and screening are energy-intensive – energy constitutes a third of a mine’s operating expense).
On-line analysis
Noticeably, trends worldwide in mining projects substantiate that on-line belt analysis is a viable alternative technique for monitoring ore grade. In online analysis, there is a wide range of options readily available, mainly: XRF (X-Ray Fluorescence), PGNAA (Prompt Gamma Neutron Activation Analysis), and Laser-Induced Fluorescence (LIF). It has to be pointed out that every method has its own merits and demerits. The merits are a result of using a suitable technology for the intended field of application. Otherwise, the wrong usage is tantamount to the folly of using a square peg in a round hole – the odds of getting the desired outcome are zilch.
X-ray fluorescence (XRF)
Fascinatingly, there is growing confidence in XRF as one of the options in on-line belt analysis. XRF is a non-destructive analytical technique used to determine the elemental composition of materials. The instruments used are capable of acquiring geochemical data rapidly.
In no doubt, the benefits of XRF become more evident when the limitations of traditional methods are thoroughly analysed.
Traditional methods fall short
As already stated, in the mineral processing value chain, the earlier the quality and grade of the ore or any material transported via a conveyor belt between various stages is determined the better. Ideally, this should be carried out by taking several samples consistently and sending them to the laboratory as and when needed. Nonetheless, in reality, the traditional method of sending samples to the laboratory for analysis falls short. There are always delays in time for delivery and sampling errors, out of kilter with the current realities in the mining sector. Regarding sampling errors, there is always the possibility of discrepancies in the material flow recorded periodically (minute by minute or hour by hour). It is wrong to assume that the material will be homogeneous. The rule of the thumb is using a technique in the correct application. Otherwise, it won’t have the desired results.
The convenience of on-line analysis XRF technique
On-line XRF analysis, using the technique of XRF in this context, guarantees non-destructive, accurate, real-time measurement and analysis data continuously, in time, of almost the whole volume of material on a conveyor belt. In most cases, correct usage ensures that elementary sample errors, which are inherent in traditional sampling methods, are eliminated or significantly minimised. What’s more, the data is available, right at the fingertips of process engineers as and when needed. This informs the decisions they make.
In XRF, the elemental composition of a sample is gauged by measuring the fluorescence X-ray (secondary ray) using analysers. The primary X-ray targets a sample, which emits a secondary ray with a set of X-Ray lines (fingerprint) unique to a specific element. Small wonder, XRF spectroscopy is widely regarded as the technology of choice where there is a need for both analysis of quality and quantity of material composition.
XRF analysers positioned above the belt (cross-belt analysers) are more convenient as a wide part of material and ore flow is exposed. Small wonder, increasingly, XRF is enjoying usage in a wide range of commodities such as iron, chrome, titanium, copper, zinc just to cite a few.
Massive gains
In a word, when used in a correct application in mines and processing plants, there are massive gains to be had in early sorting through XRF:
- Cutting costs (energy, water, and chemicals, amongst others) by ensuring that waste rock is not erroneously sent for phases of crushing, grinding, and flotation;
- Delivers immediate results (the adage time is money is not a cliché in mineral processes);
- Timely interventions where changes are needed;
- Optimises process efficiency; and
- Consistent product quality.
All told, from the aforesaid, in the mineral processing chain where there is a need for sorting at early stages on conveyor belts there is a compelling basis for adopting XRF analysers.
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Application and type of material determine choice
There is no better convenience than the availability of distinctly different technologies for online geochemical elemental analysis. However, this can also be a source of confusion. And that’s where informed choice is paramount. It is important to note the capabilities of each technology and what will best suit the intended application and type of sample material under interest.
It must be reiterated that XRF may be the end-all, be-all. Thus, the following are basic aspects of the other technologies worth grasping:
Both near-infrared (NIR) and laser-induced fluorescence (LIF) emit energy to the surface of the material. The characteristics of the material are analysed based on how the energy is reflected.
PGNAA produces high-energy gamma rays from the sample material. It requires a high-energy source of neutrons for the analysis. The drawback is that it uses radioactive sources and thus, a source of health and safety risks. PGNNA has established a fertile niche in cement production applications.
Baltic Scientific Instruments produces the CON-X On-line XRF Conveyor Analyzer.
Equipment fabricated by Baltic Scientific Instruments (headquartered in Riga, Latvia) is widely used in mining and metallurgical industries, in the nuclear industry and in environmental monitoring, security and scientific applications in global markets. One of the latest BSI developments is a mobile facility for gold ores gamma-activation analysis.
Gamma-activation analysis (GAA) is a method uniquely suited to the analysis of ore samples for gold, other precious metals and complementary elements. It is based on the irradiation of ore samples with high energy gamma quanta generated by a linear accelerator and detection of the induced activity of the excited gold nuclei by a gamma spectrometer. The high penetrating power of gamma radiation facilitates the analysis of large samples, eliminating the need to crush and grind the sample, while offering the following advantages over conventional methods:
- a significant increase in the accuracy of the analysis representation;
- reduced analysis time due to the short half-life of excited gold nuclei: just 20-30 secs;
- sufficient analysis sensitivity, accuracy, selectivity, representativeness and productivity required for modern gold mines. For gold ore content up to 1 ppm, measurement deviation of 8% or below, while ore content with up to 10 ppm comes with a deviation of 4% or below;
- consistent analysis results regardless of chemical composition of the sample;
- no negative impact on the environment: the induced activity of the sample decreases to background levels several minutes after analysis is concluded;
- non-destructive processing of ore samples, allowing repeated analysis of ore sample;
- the method allows multi-element analysis over the course of a single cycle and measurements;
- ability to automate the GAA analysis; and
- can be incorporated into a quality control/assurance process for gold mining and extraction of particular minerals and elements.
For applications where such high detection sensitivity as parts per million offered by GAA is not essential or cost-justified, Baltic Scientific Instruments produces the CON-X On-line XRF Conveyor Analyzer. This XRF analyzer is used to identify and measure the concentration of the elements and minerals in ores and materials on a conveyor belt. The analyzer detects elements from Al (Z=13) to U (Z=92). It can be easily attached to a flow-line at digging locations and mines, and has proved itself reliable in the following applications:
- Analysis of iron ore and concentrates
- Analysis of iron (as a trace element) in sand
- Analysis of chromite ore and concentrates
- Analysis of copper ore and its concentrates
- Analysis of zinc ores
- Analysis of polymetallic ores (zinc, copper, lead)
- Analysis of cobalt content in ores and concentrates
- Analysis of rutile and ilmenite (Ti)
- Analysis of zircon ores (Zr)
- Analysis of sylvinite (KCl)
- Analysis of nickel in a concentrated product
- Analysis of silver ore (Ag)
- Analysis of limestone (CaCO3)
- Quantitative analysis of uranium and its production waste
- Analysis of phosphatic materials
- Analysis of thorium
The CON-X On-line XRF Conveyor Analyzer features:
- The CON-X is mounted above the conveyor and identifies the elements and their concentration in the material on the conveyor
- High precision and stability of the results in severe environments: dust, low/high temperature and variable humidity
- Independence of the measurement results from lump size and relative humidity as long as the CON-X is in the allowable range (6-25 cm) from the material
- Simple and convenient operation and service
- Empty belt exclusion algorithm
- Remote support through the Internet
- Instrument control and data results provided using OPC communication, 4-20 mA output, ethernet
