|6545240||Metal scrap sorting system||Kumar||356/318|
|6147754||Laser induced breakdown spectroscopy soil contamination probe||Theriault et al.|
|5847825||Apparatus and method for detection and concentration measurement of trace metals using laser induced breakdown spectroscopy||Alexander|
|5813543||Method of sorting pieces of material||Gesing et al.|
|5628410||Classifying or sorting||Smith et al.|
|5410154||Device for detecting quality alterations in bulk goods transported on moving belt conveyors||Broicher et al.|
|5351117||Sensing a narrow frequency band and gemstones||Stewart et al.|
|5206699||Sensing a narrow frequency band of radiation and gemstones||Stewart et al.|
|5198871||Laser-induced-fluorescence inspection of jet fuels||Hill, Jr. et al.|
|5042947||Scrap detector||Potzschke et al.|
|4423814||Separation or concentration of magnesium-bearing minerals by induced fluorescence||White|
|4365153||Detection of certain minerals of zinc, tungsten, fluorine, molybdenum, mercury and other metals using photoluminescence||Seigel et al.|
|3472375||APPARATUS AND METHOD FOR SEPARATING ORE||Mathews|
This application is a Continuation-in-Part and claims priority to U.S. patent application Ser. No. 60/313,189 filed on Aug. 17, 2001.
1. Field of the Invention
This invention deals with the evaluation of mineral ores and the identification of components in the ores and the ability to selectively determine with a high degree of accuracy the content of such ores. In specific, by using the apparatus and method of the present invention, wanted or unwanted chemical species can be identified, thus making this an effective screening tool for rapid analysis of ores in mining applications. It is also anticipated that the present invention may be deployed in any application for which the identity of a chemical species is sought.
2. Description of Related Art
The need for instantaneous evaluation of mineral contents on moving belt systems has led to the necessity of remote sensing techniques to instantly differentiate between corresponding minerals to select desired mineral ores from those that are undesirable. This selection may be based on selective influence of the different kinds of irradiation on those minerals, whereby discrete pebbles are analyzed within a fraction of a second for a characteristic that can distinguish between “accept” and “reject” fractions. At present when dealing with moving belt systems, mineral evaluation is mainly performed using photometric, radiometric, steady-state luminescence, gamma-ray or X-ray fluorescence, and neutron absorption characteristics are mainly used for mineral evaluation.
U.S. Pat. No. 4,365,153 to Siegel describes the detection of certain minerals, including zinc, tungsten, fluorine, molybdenum, mercury, and other metals using a photoluminescence method. The basis of selective detection is that the lifetimes of photoluminescent emissions of many industrial minerals are much longer than the lifetimes of photoluminescent emissions of background materials that are likely to occur at the Earth's surface. The measurement of the photoluminescent response measured here is based on a response-retention factor and not on a direct readout at the time of irradiation. The detection here is based on taking a delayed readout to identify the minerals of economic interest after enough time has elapsed to enable unwanted sources of photoluminescence to decay.
Broicher (U.S. Pat. No. 5,410,154) describes detection of quality alterations contained in goods as they progress on a moving belt. The use of laser-induced luminescence, reflected light, and temperatures including detection of signal intensity and the fading behavior of the signals in definite spectral ranges is disclosed. This approach was also used by AIS Sommer GmbH of Germany, in their laser-induced fluorescence (LIF) analyzer for quality control in minerals and mineral processing. The LIF analyzer includes two light detector systems with three photomultipliers each, which evaluate three spectral bands in two time windows each. Such a system was employed in the Kirumna phorphorus iron ore mine in Sweden.
The limitation of LIF analysis is that its accuracy depends on the complexity of the composition of the ore and the concentration and fluorescence properties of the critical minerals in relation to all the other minerals present.
Another approach to differentiation of samples is described by White (U.S. Pat. No. 4,423,814). Here the natural luminescence of the accept and reject fractions is similar. The basis of separation of magnesium-bearing ore particles is obtained by first conditioning the exposed magnesium-rich mineral with a surface coupling agent of hydroxquinoline, then irradiating the conditioned ore to excite and induce fluorescence and then effecting separation of the magnesium-rich minerals from the lean ore particles by detection of the difference of the intensity of the fluorescence. This method detects ores having high magnesium contents on the surfaces of the pebbles.
Many similar methods have been used in the past to screen samples based on physico-chemical properties. Another example of this is selective flotation of phosphates and dolomites. As stated above, the difficulties of selective flotation of phosphates with high magnesium content are explained by similar physico-chemical properties of phosphates and dolomites. This problem exists also with other ores, thus making it desirable within the mining field to find separation systems that can quickly distinguish between wanted and unwanted ore fractions.
Alexander (U.S. Pat. No. 5,847,825) describes a method and apparatus for detection and concentration measurement of trace metals using laser-induced breakdown spectroscopy (LIBS). LIBS is a simple, rapid, real-time analytical technique based on the analysis of the spectral emission from laser-induced sparks or plasma. Pulsed laser radiation is first focused to a small spot on the sample material. When power densities exceed hundreds of MW/cm
It has been shown that LIBS is practical in situations, which require very fast, real-time measurements with no sample preparation. One such method is a penetrometer system for subsurface spectral analyses; such a system being described in Theriaul et al. (U.S. Pat. No. 6,147,754). Here, elemental identification using a cone penetrometer unit is achieved by using atomic spectral analyses of contaminants that are stimulated by a laser-induced breakdown of the soil containments to be determined.
Potzchke (U.S. Pat. No. 5,042,947) describes a scrap detection system using another LIBS system. Here a method and apparatus is disclosed whereby metal particles are detected in the context of being contained in compositions of alloying metals. Sorting of metal particles is effected by a plasma process, which cleans and then identifies the particles of interest. However, these metal particles are not in ion form as are those contained in mineral samples.
It is therefore an object of the invention to provide a LIBS system that is capable of detection of trace metals in an ore sample, such metals even being in an ionic species form.
It is a further object of the invention to provide a low-cost multi-element analysis system adapted to being compact and requiring no sample preparation.
It is another object of the invention to provide a system for sorting mineral ore samples which allows for rapid sorting of minerals in a moving belt system.
The present invention comprises a system and a method for mineral sorting and detecting, including remote sensing, and more particularly, for real-time detection and content evaluation of minerals or trace concentrations of elements in materials as they are conveyed on a moving belt. The instant invention employs a laser-induced breakdown spectroscopy (LIBS) system wherein intensity ratios of the emission lines characteristic for specific elements or minerals enable detection of the same while on a moving belt. Because associated minerals have different chemical compositions, namely, major or minor elements, the relative intensities, defined by their characteristic spectral lines, enables all phases to be consistently identified and assessed within a short time that is consistent with both LIBS and the moving belt system.
The steps to the invention include establishing a spectral signature ratio for at least one predetermined substance, the signature having a first intensity at a first wavelength relative to a second intensity at a second wavelength, applying pulsed laser energy to the mineral sample whereby plasma is produced, obtaining the spectral intensity of the plasma at the first and second wavelengths, and calculating the ratio of the spectral intensity at the first wavelength by the spectral intensity at the second wavelength whereby the presence or absence of the substance may be resolved.
It should be noted that the present invention permits the mineral sample to be analyzed substantially in real-time while in transit, such as moving on a conveyor belt. In a preferred embodiment, the steps include providing a computational processor and providing a radiation detector adapted to obtain the spectral intensity of the plasma. A database of spectral signatures for at least one substance is provided along with an output means communicatively coupled to the processor. The radiation detector, processor, and database are all communicatively coupled together wherein the spectral intensity is obtained by the radiation detector and measured values for the first and second wavelengths are passed onto the processor which calculates and compares the ratio to the database of spectral signatures and communicates the results to the output means. In another embodiment of the invention, the step of obtaining of the spectral intensity of the plasma may be time-gated to provide further discrimination of the sample's plasma.
The present invention is not limited to minerals, but to any compound for which the identity is sought in rapid analytical fashion. For example, food products (i.e., ingestible matter) may be rapidly analyzed for compounds or elements of interest.
A detailed description of preferred embodiments of the present invention will now be presented with reference to
The instant invention includes an system and method for the identification of specific species in an ore sample. This is useful for the evaluation of phosphate with high dolomite content, but is not intended to be limited thereto, as the system and method also are applicable to other elements, ions, or compounds occurring in mined mineral ores. The detection of those ions is performed by a source of irradiation, such as a laser energy emitter or other suitable excitation source, and means for delivering to and focusing the irradiation, i.e., the laser energy emission, on a sample on a moving belt, or other conveyor means. The system further comprises a detection system and, in a preferred embodiment, a processor.
Selecting an ionic or elemental species in the desired fraction and performing a screening based upon an intensity ratio I
The laser source range of an illustrative embodiment encompasses, but is not intended to be limited to, ˜100-1000 Hz, with pulse energy of no less than 10 mJ. It is contemplated that the laser system may be selected based on subject ion or element, as being known to one of ordinary skill in the art. In addition to laser sources, a suitable excitation source may be employed after the subject wavelengths are determined; this excitation source being chosen based on the ion emission lines and the desired excitation wavelength desired.
Spectral analysis refers to a determination of the intensity of light as a function of wavelength. Any means of spectral analysis known in the art may be used, again, the choice being dependent on the particular application. In a preferred embodiment of the present invention, it was found to be desirable to use a ⅛-mm imaging spectrograph and an intensified thermoelectric-cooled ICCD camera, which is capable of imaging up to 500 spectra/second.
In order to differentiate between wanted and unwanted ore samples, an intensity ratio, /
In addition, comparative spectra are then obtained using different power levels and different excitation wavelengths for the laser source. In addition, studies of the decay times of the different lines are made for use with time-resolved spectroscopy. The /
The presence of a sample fraction in the stream is determined by measurement of its specific emission line intensities. The relative content of selected fraction is determined by the ratio between the numbers of the emission pulses associated with the selected fraction to the total number of emission pulses. This ratio is determined by an investigation of the mineral species contained in the subject ore fractions, both the “good” (wanted) ores and the “bad” (unwanted) ores.
The ratio technique of the present invention is suitable for ore samples having particle sizes from micrometer to large boulder sizes. It is within the scope of the invention to provide a portable version of the system, which provides an effective means of analyzing mine facial or perform in situ examinations within the mining site itself. The system may be applied to moving systems of all varieties known in the art; these including, but not limited to, flow cells, slurry systems, flotation systems, and other moving bed systems known in the art. These also include mechanical movement as well as chemical movement means. Because the ratio of the emission lines is determined for the subject ores from a specific location, the presence of organic impurities, water, other flocculents, and slurry agents or impurities does not affect the results, since the ratio is made from emission lines selected for their spectral purity. Indeed, any line that exhibits such interference is not of interest for establishment of the intensity ratios of the present invention.
In a further embodiment, the spectral analysis data can be output to a computer with a display monitor, combined with an electronic card or having an algorithm that enables the laser beam to synchronize with the ICCD, to measure two emission signals from two different pixels simultaneously, to calculate their ratio, to identify accept or reject fractions according to the ratio, to demonstrate the place of corresponding mineral on the computer screen, and then calculate the subject fraction content of desired or undesired ions or elements.
With respect to phosphate rocks, the intensity ratio of the characteristic emission lines of Mg at 518 nm and F at 604 nm enables a detection of pebbles having high dolomite content. Because dolomite (Ca, Mg)(CO
The analytical line of Mg at 518 nm is characterized by a decay time of approximately 200 ns. This makes for an optimal time-resolution spectrum with a narrow gate of 1 μs. Under such conditions the intensity of the relatively broad band in the range 600-630 nm connected with carbonate is substantially lower, and the ratio /
The system and method of the present invention are further characterized by the following example.
Example 1 Use of LIBS to Differentiate Florida Phosphate Ores
Natural apatite contains several characteristic luminescence centers that enable differentiation from dolomites (FIG.
In order to find a distinguishing or “fingerprint” characteristic ion for identifying dolomite and apatite, ICP-MS analysis of Florida phosphates was performed. It was found that apatite contained rare earth elements, and in the case of the Florida apatites, these were present in quantities suitable for laser-induced luminescence analysis. As seen in Table 1, the highest concentration and quantum efficiency is for Ce
To further investigate the efficacy of the Dy
The >200 samples were classified and identified as follows: Fraction +½ in. Twenty-two samples having sizes greater than ½ in. were randomly chosen from the light-colored part of the ore: 9 were identified by X-ray diffraction as apatite and 13 as dolomite. By laser-induced time-resolved luminescence (LITRL), 6 apatites clearly demonstrated Dy
Thirteen samples were randomly chosen from the dark-colored part, and all were identified by X-ray diffraction (XRD) as apatite. Dy
Twenty-nine samples having sizes greater than ⅜ in. were randomly chosen from the light-colored part: 15 were identified by XRD as apatite and 14 as dolomite. By LITRL, 6 apatites clearly demonstrated Dy
Twelve samples were randomly chosen from the dark-colored part: 10 were identified by XRD as apatite and 2 as dolomite. Dy
Sixteen samples having sizes greater than 0.156 in. were randomly chosen from the light-colored part: 10 were identified by XRD as apatite and 6 as dolomite. By LITRL, 8 apatites (80%) clearly demonstrate Dy
Twelve samples were randomly chosen from the dark-colored part: 11 were identified by XRD as apatite and 1 as dolomite. Dy
Thirty-one samples having sizes greater than 16 mesh (approx. 1 mm) were randomly chosen from the light-colored part: 25 were identified by XRD as apatite and 6 as dolomite. By LITRL, 20 apatites (80%) clearly demonstrated Dy
Twelve samples were randomly chosen for the dark-colored part, and all were identified by XRD as apatite. Dy
Twenty-three were randomly chosen from the light-colored part: 16 were identified by XRD as apatite and 7 as dolomite. By LITRL, 9 apatites (56%) clearly demonstrated Dy
Twelve samples were randomly chosen from the dark-colored part, and all were identified by XRD as apatite. Dy
Eighteen samples were randomly chosen for the light-colored part: 15 were identified by XRD as apatite and 3 as dolomite. By LITRL 11 apatites (73%) clearly demonstrated the presence of Dy
Twelve samples were randomly chosen from the dark-colored part: 11 were identified by XRD as apatite and 1 as dolomite. Dy
The results of these studies are tabulated in Table 2, the data of which indicate that the main object is the light-colored fraction, where the average dolomite content was 33%, while that in the +½ fraction was nearly 60% and in the +⅜ fraction, more than 50%. The dark-colored fractions usually contained 1% dolomite.
In order to address the problem that Dy3+ luminescence intensity varies strongly from apatite to apatite, an optimal excitation band was chosen. It is well known that Dy3+ has very narrow excitation bands, this being confirmed by the fact that in the apatite it is strongly excited by 355-nm radiation, but absolutely not at 337 nm.
In an additional embodiment, the sensitivity was improved by computerized spectral analysis using smoothing, which achieves an improvement of the signal-to-noise ratio by mathematical processing of the raw data. A widely used method of spectral data smoothing in the art is the moving window and polynomial curve fitting (the Savitzky-Golay method). This method also includes simultaneous processing of the data to locate peaks by the calculation of the spectrum derivatives. The moving window scans spanning M data points, moves along the data, and creates an estimation of smoothing spectrum or its derivative in the inner window point.
In order to computerize the analysis of spectral data, a software program was written containing the following elements:
1. Reading of the ASCII files
2. Smoothing by the Savitzky-Golay method (SGM)
3. Calculation of the first and second derivatives of spectrum data by SGM
4. Calculation of background by the least-squares method
5. Peak searching
6. Calculation of the peak amplitude above the background
7. Storing the results in Microsoft Excel files
The significant difference between apatite and dolomite is the presence of a peak near 483 nm in the apatite spectrum that is not present in the dolomite spectrum.
The purpose of the first step of the analysis is smoothing of spectra and checking for a peak in the 483-nm area. A 5-point SGM has been used for smoothing, which gives effective results for increasing the signal-to-noise ratio. It was determined that all apatite spectra have peaks in the 483-nm region (the average wavelength of the peak maximum is 483.250 nm, with a standard deviation of 1.572 nm). At that time only 7 of the dolomite spectra demonstrated a peak in this area (average wavelength 483.219 nm, standard deviation 2.144 nm).
Background calculation was made by the least-squares method. The parabolic approximation of the background gave satisfactory results, and the peak amplitude over the background was calculated for all spectra. This analysis showed that peak amplitude above the background for the apatite spectra is much higher than for the dolomite spectra. For apatites, the average value is 9.74%, with a standard deviation of 6%, while for dolomites the average value is 0.91%, with a standard deviation of 2.21%.
In a further study of Florida apatite and dolomite, a light pulse of the 3 d harmonic of a Nd:YAG laser (355 nm, 30 ns) was used for luminescence excitation. The luminescent light after passing through the monochromator assembly comprising the crystals
Further modifications of the apparatus
To overcome another problem caused by the time-delay system, another approach to the gating aspect was employed. Owing to the large resistance of the output PMT, the “tail” from the fast non-characteristic luminescence component still hid the weaker Dy
A further embodiment utilizes LIBS.
Example 2 Use of LIBS for Apatite and Dolomite Differentiation
The dual PMT system was used to inspect 160 pebbles obtained from a Florida source. These were analyzed in a condition similar to a moving-belt system, namely, from a distance of 1 meter using only one laser pulse. Three groupings were made, and each of these was separated into “bad” as containing dolomite and “good” as being apatite. In addition, an outside laboratory to determine the constituents performed a separate chemical analysis. Those results are contained in Table 3, which illustrates that the “bad” fraction contained mainly dolomite with the mean /(MgO)//(P
The identification can also be enhanced by use of time-resolved spectroscopy. As shown in
One potential problem with analysis of raw ore samples is interference due to water in the material.
The description above should not be considered as limiting the scope of the invention, but as merely providing illustration of some of the preferred embodiments of the instant invention. In light of the above description and examples, various other modifications and variations will now become apparent to those of ordinary skill in the art and are therefore considered within the scope of the invention without departing from the spirit and scope of the invention.