WO2002008738A1

WO2002008738A1 - On-line x-ray diffraction analyser

Info

Publication number: WO2002008738A1
Application number: PCT/AU2001/000901
Authority: WO
Inventors: Ian Charles Madsen; Jonian Ivanov Nikolov
Original assignee: Commonwealth Scientific And Industrial Research Organisation
Priority date: 2000-07-24
Filing date: 2001-07-24
Publication date: 2002-01-31
Also published as: AUPQ893700A0

Abstract

An apparatus (1) for on-line analysis by X-ray diffraction of an aqueous slurry stream of a solid/liquid mixture is provided. The apparatus (1) consists of an inflow conduit (2) for receiving a sample of the slurry stream. The conduit is connected to a distribution chamber (3) which causes the slurry sample to enter an analysis region (4) where X-ray diffraction measurements are conducted using reflectance techniques from a radiation source (11) and a wide angle detector (12). The sample is then returned to the aqueous slurry stream. The distribution chamber (3) imparts centrifugal motion to the slurry sample thereby presenting a flat surface over the analysis region (4).

Description

ON-LINE X-RAY DIFFRACTION ANALYSER Technical Field of the Invention

This invention relates to an apparatus for performing X-ray diffraction analysis and in particular relates to performing X-ray diffraction of solid/liquid mixtures in a processing line environment. The invention also relates to a method for analysing solid/liquid mixtures using x-ray diffraction analysis. Background of the Invention

Over the years, a specialised field of materials analysis has developed in which X-rays are diffracted off sample materials. Every crystalline material has a unique composition formed of regular, periodic spacings of electron densities. These are often referred to as "d-spacings" or "lattice spacings". Each compound has its own set of lattice spacings. Knowledge of the spacings is utilised to determine the compounds of which a particular material is composed. To date X-ray diffraction has primarily been performed on randomly oriented powdered materials in order to determine composition or on perfect, single crystals, in order to obtain a structure solution.

Powder X-ray diffraction analysis has mainly been confined to material investigations conducted on materials away from a processing or on-line environment. However, as in most specialised fields, traditional applications are being extended to new methods of analysis. Just as X-ray diffraction has advanced to enable measurement of materials properties such as orientation and grain stress, to improve the usefulness of this analysis technique the use of X- ray diffraction as an analysis technique for on-line processing streams would be highly advantageous in the control of the material properties of the stream. This is particularly the case in the mineral processing industry. As an on-line analysis it is desirable for the concentration of the slurry to be the same as in the process. For mineral processing this may be approximately 40% v/v.

As many material transport mechanisms of solids involves forming a slurry or other solid liquid mixture of the particulate material with water, it would be advantageous to be able to use X-ray diffraction analysis to measure the properties of materials in such a transport stream.

The invention of US 4,090,073 discloses a method of using X-ray diffraction to determine the mineral composition in an aqueous mineral slurry. However this method is not as effective as desired, since it relies on the collection of a limited range of the X-ray pattern. High energy (short wavelength) X-rays are required for the transmission mode required in this prior art invention. These high energy X-rays produce a compressed pattern and discrimination between peaks can be difficult.

US Patent 5,107,527 incorporates a combination of X-ray diffraction and X-ray fluorescence analysis. The use of this combination limits the ability to use wide angle data collection in X-ray diffraction. This invention also requires a window in the sampling cell. Summary of the Invention

In one aspect the invention provides an apparatus for on-line analysing a stream of solid/liquid mixture including a means for removing a sample flow from the stream of solid/liquid mixture, a means for preparing and presenting the sample flow with a substantially flat upper surface to a measurement station for X-ray diffraction measurement, a measurement station including an X-ray generator and position sensitive detector for detecting X-ray diffraction patterns from the prepared sample flow, and processor means for analysing the X-ray diffraction patterns to determine the composition of substances in the sample from each diffraction pattern and for providing a series of sequential composition determinations thereby representing the composition of the substances in the sample flow wherein the position sensitive detector for detecting the X-ray diffraction patterns of the sample is a curved position sensitive detector or area detector capable of simultaneous collection of a wide angle range of the X-ray diffractogram. This offers an improvement over the use of a sequential detector for establishing a diffractogram in a series of measurements. In a second aspect of the invention, there is provided an apparatus for presenting a sample from a solid/liquid material flow for X-ray diffraction measurements, the apparatus having an inflow conduit with an inlet for receiving the sample flow from the material flow, the conduit communicating with a distribution chamber, the distribution chamber communicating with an analysis region and an apparatus discharge, whereby the sample flow passes through the distribution chamber to the analysis region before passing to the apparatus discharge, and wherein the distribution chamber is adapted to provide a substantially flat upper surface of the sample flow in the analysis region.

The distribution chamber preferably diverges outwardly from the conduit and is provided with a plurality of outlets to the analysis region.

The apparatus preferably further includes a motion generation means for imparting centrifugal motion to the solid/liquid sample flow in the distribution chamber. The motion generation means preferably rotates the distribution chamber about an axis. The rotational axis of the distribution chamber preferably extends through the in flow conduit and may be co-axial.

Preferably the X-ray diffraction is conducted in reflection mode. Preferably the substantially flat upper surface of the sample flow has no window or other barrier between this surface and the X-ray radiation source.

Preferably wide angle data collection is used to detect the reflected/refracted radiation.

According to a third aspect of the invention, there is provided a method for continuously presenting a sample from a stream of solid/liquid mixture containing crystalline substances including the steps of: extracting a sample flow from the stream; - feeding the sample flow continuously upwardly into a distribution chamber, imparting a centrifugal motion to the sample flow as it passes upwardly through the distribution chamber to an analysis region in the distribution chamber thereby presenting a substantially flat upper surface of the sample flow to an X-ray radiation source for performing X-ray diffraction measurements, and continuously discharging the sample from the distribution chamber. Without being limited by the following explanation, it is believed that the centrifugal motion imparted to the sample counteracts surface tension forces in the upper surface of the solid/liquid sample, presenting a flat surface over the analysing region through which the X-ray diffraction measurements are performed.

In accordance with a fourth aspect of the invention, there is provided a method of analysing a stream of solid/liquid mixture including:

1. extracting a sample flow from the stream of solid/liquid mixture,

2. preparing the sample flow for X-ray diffraction measurements by (a) feeding the sample flow upwardly into a distribution chamber, and (b) imparting a centrifugal motion to the sample flow passing from the distribution chamber to an analysis region, thereby presenting a substantially flat upper surface to an X-ray radiation source,

3. directing an X-ray beam into the sample flow in the analysis region as it passes through a measurement station and detecting diffracted X-rays over an angular range to provide a diffraction pattern,

4. analysing the diffraction pattern to determine a composition for substances in the sample, 5. repeating step (3) to provide diffraction patterns from the continuously moving samples at predetermined intervals, and 6. repeating step (4) for each diffraction pattern from step (5). Detailed Description of the Invention

It will be appreciated that the methods described under The Summary of the Invention can provide a wide angular range, typically up to 120°, diffraction pattern at short intervals from a continuously moving sample. The series of sequential composition determinations from such patterns represents the composition of the solids in the stream of solid/liquid material substantially in real time. The series of composition determinations also gives effectively a "continuous" analysis of the solids in the stream of solid/liquid material (the term "continuous" in this context meaning continuing discreet compositional determinations separated by short time intervals).

The continuous withdrawal of a sample from the process stream allows its analysis on a continuous basis and thus the provision of substantially real time or current production data on which decisions can be made to control the process. Such control may be effected automatically, for example as in a closed loop feedback system, or manually by a process operator.

X-ray diffraction analysis of solids in a solid/liquid mixture is only able to analyse the crystals of the material largely at the surface of the solid samples presented to the X-ray diffraction instrumentation. As the focus of the X-ray beam on the sample is tight, for example an area of the order of 10-30 mm² (typically 10 mm long x 1-3 mm wide) the more sample that is presented for analysis, the higher the confidence that the result is representative of the material in the process stream. It is also important for accuracy that the sample surface be very smooth and substantially flat.

In this invention the term slurry is used in its art recognised sense and means solid material mixed with a liquid. Embraced within this definition are sludges.

The features objects and advantages of the present invention will become more apparent from the following description of the preferred embodiment and accompanying drawings in which:

Figure 1 is a diagrammatic representation of the main components of an apparatus embodying the invention,

Figure 2(a) is a plan view of the distribution chamber in Figure 1, Figure 2(b) is an exploded side view of region A in Figure 2(a), Figures 3(a) and 3(b) are XRD patterns using a mylar window and pure water respectively,

Figures 4(a) and 4(b) show graphs of the XRD pattern for control solid/liquid sample with 50% v/v and 25% v/v solids respectively, Figures 5(a) and 5(b) are XRD patterns for control solid/liquid samples with 18% v/v and 5% v/v solids respectively,

Figure 6 is a schematic view of an apparatus according to the present invention with X-ray source and detector.

Referring to Figure 1, the apparatus illustrated has a stage 1 including an upwardly flowing conduit 2 communicating with a distribution chamber 3. The distribution chamber 3 is preferably mounted for rotational movement by a drive means (not shown). Alternatively the whole stage may be rotated to provide the desired centrifugal action.

The upper surface of the distribution chamber is provided with a plurality of outlets 5 to an analysis region 4. Figure 2(a) shows outlets 5 located in the upper surface 9 and Figure 2(b) shows an enlarged sectional view of an outlet 5.

The size and location of these holes or outlets are selected so as to provide a substantially flat upper surface of the sample flow in the analysis region. By substantially flat we mean that interference from an irregular surface is reduced to a sufficient extent that meaningful data may be obtained in an analysis. The stage 1 may be any shape but a frusto conical or cylindrical shape is preferred.

Below the distribution chamber 3 is a floor 7 above which defines a slurry tray

8. In the slurry tray 8 above the distribution chamber 3 is the analysis region of the stage. Radially outwardly from the analysing region is a sample discharge which may be an annular sleeve 6 provided to receive sample flow from the analysing region.

In operation, as a solid/liquid mixture sample enters the distribution chamber 3 of the stage 1. The sample may be withdrawn from the slurry stream by use of a pump. The rotational motion of the chamber imparts a centrifugal motion to the sample as it progresses through the chamber. Liquid effective seals are provided at appropriate places such as between the distribution chamber 3 and the conduit and rotational shaft drive for the distribution chamber and the conduits. This centrifugal motion is believed to counteract the surface tension forces on the surface of the sample providing a flat surface over the analysing region. The centrifugal motion further has the benefit of progressing the analysed sample towards the discharge in distribution for X-ray measurements of the next sample.

The outlets 5 from the distribution chamber 3 may also have a lateral discharge component thereby imparting a lateral motion to the slurry as it exits the distribution chamber 3. By careful design and control of the sample pumping through the conduit the centrifugal or swirling motion can be imparted to the sample without rotation of the distribution chamber 3 or stage 1. The pumping rate of the sample from the slurry stream may also be used to influence the attainment of the desired substantially flat upper surface of the sample flow in the analysis region.

The outlets 5 may also be progressively larger towards the outer edges of the upper surface 9 of the distribution chamber 3. There may also be some advantage to slurry suspension by providing outlets upwardly oriented in the side of the chamber 3.

As shown in Figure 6, the measurement station 10 includes an X-ray source 11, and a position sensitive detector in the form of an area detector, 12 (120°), to detect diffracted radiation in the reflection mode. A suitable processor means (not shown) receives signals from detector 12 and presents the measurements in a desirable format. Use of an area detector is preferred, although use of other types of detector such as single point detectors combined with a goniometer to sequentially measure the XRD pattern is also possible. The area detector may collect the diffractogram over an angular range of 120° 2θ, typically spanning, 1° - 121° 2θ, but other ranges may be selected. The X- ray diffraction instrumentation of the diffractomoter includes other components such as a tube stand and X-ray collecting devices.

As an example, the XRD instrumentation consists of the following - (i) INEL 3kw X-ray generator with RS232 interface to power the XRD tube.

(ii) Philips, cobalt target, long fine focus XRD tube rated at 1800W. (iii) Graphite monochromator to remove unwanted wavelengths and 0.2mm slits to define the beam size at the sample. The use of a multilayer mirror in place of the monochromator to increase the pattern intensity is recommended.

(iv) INEL CPS120 area detector to detect the XRD pattern plus a panel of electronics to process signals from the detector, (v) Industrial computer built into the system to control data collection, analysis and result reporting. Data is collected using software specifically designed and coded for interaction with the INEL detector. Data can be collected for times ranging from 1 to 1000 seconds and summed over as many data sets as deemed necessary to obtain appropriate counting statistics. One example of such settings are 60 second data collections with 10 data sets summed for analysis providing analyses every minute after the first 10 minutes. The XRD data can be analysed using the "whole pattern" or Rietveld based approach, but other analytical techniques may be used.

The apparatus of the invention is preferably located (and consequently the method performed) in an air conditioned room to avoid instrument distortion due to temperature changes and to ensure protection of the electronic equipment. A representative sample of a product stream can be conveyed into such a room located in proximity to the product stream. The invention is suitable for any slurry process stream that can be transported from the processing line to the instrument. Examples of X-ray spectra are illustrated in Figures 3 - 5, with Figures 3(a) and (b) showing reference spectra using Mylar window (3a) and water (3b). The slurry used in these experiments was a sample of concentrate from a lead-zinc smelter. It is desirable in commercial applications that the data quality is reasonably consistent over typically 25% - 50% by volume. Figures 4(a) and 4b) demonstrate this consistency at 25% and 50% volume solids when run for 600 seconds. Figures 5(a) and 5(b) illustrate the substantially poorer data when the sample had 18% and 5% by volume concentration. The poorer results at these lower volume concentrations is attributed to the influence of the water. The spectrum for water is shown in Figure (3b). Although able to be used for slurries at these lower volume concentrations the apparatus provides better data at higher volume concentrations. There are several advantages to not needing a window between the sample flow and the radiation source. . It has advantages in not interfering with analysis as there is no additional material in the beam path. This is illustrated in Figure 3(a) where the spectrum using a Mylar window is shown. Peaks attributed to the Mylar window are those with an intensity of about 500 counts at 26 degrees and some of the "lumping" between about 10 and 40 degrees. These peaks are in areas that are of relevance for mineral slurries, as can be seen in Figures 4(a) and 4(b). It can be seen that this would interfere with data from the slurry sample. The absence of a window also overcomes potential wear and scratching of window from abrasive slurries. This design also allows small incidence angles and reliable monitoring of phases with "large unit cell parameters"

It will also be appreciated that various modifications and alterations may be made to the preferred embodiments above, without departing from the scope and spirit of the present invention.

Claims

1. An apparatus for one-line analysing a stream of solid/liquid mixture including, a means for removing a sample flow from the stream of solid/mixture, a means for preparing and presenting the sample flow with a substantially flat upper surface to a measurement station for X-ray diffraction measurement, a measurement station including an X-ray generator and position sensitive detector for detecting X-ray diffraction patterns from the prepared sample flow, and processor means for analysing the X-ray diffraction patterns to determine the composition of substances in the sample from each diffraction pattern and for providing a series of sequential composition determinations thereby representing the composition of the substances in the sample flow wherein the position sensitive detector for detecting the X-ray diffraction patterns of the sample is a curved position sensitive detector capable of simultaneous collection of a wide angle range of the X-ray diffractogram.

2. An apparatus for presenting a sample from a solid/liquid material flow for X-ray diffraction measurements, the apparatus having an inflow conduit with an inlet for receiving the sample flow from the material flow, the conduit communicating with a distribution chamber, the distribution chamber communicating with an analysis region and an apparatus discharge, whereby the sample flow passes through the distribution chamber to the analysis region before passing to the apparatus discharge, and wherein the distribution apparatus is adapted to provide a substantially flat upper surface of the sample flow in the analysis region.

3. An apparatus as defined in Claim 2 wherein the distribution chamber diverges outwardly from the conduit and is provided with a plurality of outlets to the analysis region.

4. An apparatus as defined in Claim 2 or Claim 3 wherein the apparatus further includes a motion generation means for imparting centrifugal motion to the solid/liquid sample flow in the distribution chamber.

5. An apparatus as defined in Claim 4 wherein the motion generation means preferably rotates the distribution chamber about an axis.

6. An apparatus as defined in Claim 5 wherein the rotational axis of the distribution chamber extends through the inflow conduit.

7. An apparatus as defined in Claim 6 wherein the rotational axis of the distribution chamber and the axis of the inflow conduit are co-axial.

8. An apparatus as defined in any one of claims 1 to 7 where the X-ray diffraction is conducted in a reflectance mode.

9. A method for continuously presenting a sample from a stream of solid/liquid mixture containing crystalline substances including the steps of: extracting a sample flow from the stream; feeding the sample flow continuously upwardly into a distribution chamber, imparting a centrifugal motion to the sample flow as it passes upwardly through the distribution chamber to an analysis region in the distribution chamber thereby presenting a substantially flat upper surface of the sample flow to an X-ray radiation source for performing X-ray diffraction measurements, and continuously discharging the sample from the distribution chamber to return to the stream.

10. A method of analysing a stream of solid/liquid mixture including: 1. extracting a sample flow from the stream of solid/liquid mixture,

2. preparing the sample flow for X-ray diffraction measurements by

(a) feeding the sample flow upwardly into a distribution chamber, and

(b) imparting a centrifugal motion to the sample flow passing from the distribution chamber to an analysis region, thereby presenting a substantially flat upper surface to an X-ray radiation source.

4. analysing the diffraction pattern to determine a composition for substances in the sample,

5. repeating step (3) to provide diffraction patterns from the continuously moving samples at predetermined intervals, and

6. repeating step (4) for each diffraction pattern from step (5).