The exploitation and smelting of rare earth resources lead to serious pollution of rare earth elements (REEs) in farmland around mining area. The influence of four kinds of phosphate amendments-phosphate rock (PR), superphosphate (SSP), bone char (BC), and calcium magnesium phosphate (CMP)-on the bioavailability of REEs and the uptake and accumulation of 15 types of REE in rice were conducted in this study. Soil solutions were collected at tillering stage, heading stage and maturing stage, and rice was harvested at maturing stage. The mechanism of phosphate amendments reducing the bioavailability of REEs was studied by X-Ray diffraction and ICP-MS. PR treatment inhibited rice growth, but SSP, BC and CMP treatments all promoted rice growth, improved biomass of roots, shoots and grains, and promoted the uptake of phosphorous in rice. When compared with the CK, SSP, BC and CMP reduced the total REE concentrations in rice roots by 82.2%, 67.9% and 89.6%, shoots by 75.4%, 40.1% and 65.5%, grains by 23.8%, 29.0% and 29.3%, respectively. PR, SSP, BC and CMP significantly reduced the concentrations of REEs in the soil solution at three stages of rice growth. Analytic results of X-ray diffraction shows that adding PR, SSP, BC and CMP can lead to the formation of rare earth phosphate in the soil, thus reduce the activity of the REEs in the soil. Because SSP releases H+ during its dissolution, which has the risk of activating REEs in soil, CMP and BC are potential materials for remediation of REE-contaminated soil.
element of x ray diffraction solution
X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely ground, homogenized, and average bulk composition is determined.
Max von Laue, in 1912, discovered that crystalline substances act as three-dimensional diffraction gratings for X-ray wavelengths similar to the spacing of planes in a crystal lattice. X-ray diffraction is now a common technique for the study of crystal structures and atomic spacing.
X-ray diffraction is based on constructive interference of monochromatic X-rays and a crystalline sample. These X-rays are generated by a cathode ray tube, filtered to produce monochromatic radiation, collimated to concentrate, and directed toward the sample. The interaction of the incident rays with the sample produces constructive interference (and a diffracted ray) when conditions satisfy Bragg's Law (nλ=2d sin θ). This law relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample. These diffracted X-rays are then detected, processed and counted. By scanning the sample through a range of 2θangles, all possible diffraction directions of the lattice should be attained due to the random orientation of the powdered material. Conversion of the diffraction peaks to d-spacings allows identification of the mineral because each mineral has a set of unique d-spacings. Typically, this is achieved by comparison of d-spacings with standard reference patterns.
All diffraction methods are based on generation of X-rays in an X-ray tube. These X-rays are directed at the sample, and the diffracted rays are collected. A key component of all diffraction is the angle between the incident and diffracted rays. Powder and single crystal diffraction vary in instrumentation beyond this.
X-ray diffractometers consist of three basic elements: an X-ray tube, a sample holder, and an X-ray detector. Bruker's X-ray Diffraction D8-Discover instrument. Details X-rays are generated in a cathode ray tube by heating a filament to produce electrons, accelerating the electrons toward a target by applying a voltage, and bombarding the target material with electrons. When electrons have sufficient energy to dislodge inner shell electrons of the target material, characteristic X-ray spectra are produced. These spectra consist of several components, the most common being Kα and Kβ. Kα consists, in part, of Kα1 and Kα2. Kα1 has a slightly shorter wavelength and twice the intensity as Kα2. The specific wavelengths are characteristic of the target material (Cu, Fe, Mo, Cr). Filtering, by foils or crystal monochrometers, is required to produce monochromatic X-rays needed for diffraction. Kα1and Kα2 are sufficiently close in wavelength such that a weighted average of the two is used. Copper is the most common target material for single-crystal diffraction, with CuKα radiation = 1.5418Å. These X-rays are collimated and directed onto the sample. As the sample and detector are rotated, the intensity of the reflected X-rays is recorded. When the geometry of the incident X-rays impinging the sample satisfies the Bragg Equation, constructive interference occurs and a peak in intensity occurs. A detector records and processes this X-ray signal and converts the signal to a count rate which is then output to a device such as a printer or computer monitor. Show caption HideX-ray powder diffractogram. Peak positions occur where the X-ray beam has been diffracted by the crystal lattice. The unique set of d-spacings derived from this patter can be used to 'fingerprint' the mineral. Details
X-ray powder diffraction is most widely used for the identification of unknown crystalline materials (e.g. minerals, inorganic compounds). Determination of unknown solids is critical to studies in geology, environmental science, material science, engineering and biology.
Data Collection The intensity of diffracted X-rays is continuously recorded as the sample and detector rotate through their respective angles. A peak in intensity occurs when the mineral contains lattice planes with d-spacings appropriate to diffract X-rays at that value of θ. Although each peak consists of two separate reflections (Kα1 and Kα2), at small values of 2θ the peak locations overlap with Kα2 appearing as a hump on the side of Kα1. Greater separation occurs at higher values of θ. Typically these combined peaks are treated as one. The 2λ position of the diffraction peak is typically measured as the center of the peak at 80% peak height.
The d-spacing of each peak is then obtained by solution of the Bragg equation for the appropriate value of λ. Once all d-spacings have been determined, automated search/match routines compare the ds of the unknown to those of known materials. Because each mineral has a unique set of d-spacings, matching these d-spacings provides an identification of the unknown sample. A systematic procedure is used by ordering the d-spacings in terms of their intensity beginning with the most intense peak. Files of d-spacings for hundreds of thousands of inorganic compounds are available from the International Centre for Diffraction Data as the Powder Diffraction File (PDF). Many other sites contain d-spacings of minerals such as the American Mineralogist Crystal Structure Database. Commonly this information is an integral portion of the software that comes with the instrumentation.
Bish, DL and Post, JE, editors. 1989. Modern Powder Diffraction. Reviews in Mienralogy, v. 20. Mineralogical Society of America.
Cullity, B. D. 1978. Elements of X-ray diffraction. 2nd ed. Addison-Wesley, Reading, Mass.
Klug, H. P., and L. E. Alexander. 1974. X-ray diffraction procedures for polycrystalline and amorphous materials. 2nd ed. Wiley, New York.
Moore, D. M. and R. C. Reynolds, Jr. 1997. X-Ray diffraction and the identification and analysis of clay minerals. 2nd Ed. Oxford University Press, New York.
For more information about X-ray Powder Diffraction (XRD) follow the links below.For more information on XRD Methods, visit the USGS website
For additional information on X-ray basics (more info) ; Materials Research Lab, University of California- Santa Barbara
Rigaku Journal; an on-line journal that describes and demonstrates a wide range of applications using Xray diffraction.
Cambridge University X-ray Tutorial
International Union of Crystallography (IUCr) Teaching Pamphlets
Introduction to X-ray Diffraction (more info) --University of California, Santa Barbara
Introduction to Crystallography --from LLNL
X-ray Crystallography Lecture Notes ( This site may be offline. ) --from Steve Nelson, Tulane University
Reciprocal Net--part of the National Science Digital Library. Use the "Learn About" link to find animations of the structures of common molecules (including minerals), crystallography learning resources (tutorials, databases and software), resources on crystallization, and tutorials on symmetry and point groups.
X-ray techniques lab exercises from the SERC Teaching Mineralogy Collections
Weathering of Igneous, Metamorphic, and Sedimentary Rocks in a Semi-Arid Climate - An Engineering Application of Petrology - This problem develops skills in X-ray diffraction analysis as applied to clay mineralogy, reinforces lecture material on the geochemistry of weathering, and demonstrates the role of petrologic characterization in site engineering.
Teaching Guide to X-ray Diffraction at Cambridge
A Powerpoint presentation on use of XRD in Soil Science (PowerPoint PRIVATE FILE 1.6MB Sep7 07) by Melody Bergeron, Image and Chemical Analysis Laboratory at Montana State University.
Brady, John B., and Boardman, Shelby J., 1995, Introducing Mineralogy Students to X-ray Diffraction Through Optical Diffraction Experiments Using Lasers. Jour. Geol. Education, v. 43 #5, 471-476.
Brady, John B., Newton, Robert M., and Boardman, Shelby J., 1995, New Uses for Powder X-ray Diffraction Experiments in the Undergraduate Curriculum. Jour. Geol. Education, v. 43 #5, 466-470.
Dutrow, Barb, 1997, Better Living Through Minerals X-ray Diffraction of Household Products, in: Brady, J., Mogk, D., and Perkins D. (eds.) Teaching Mineralogy, Mineralogical Society of America, p. 349-359.
Hovis, Guy, L., 1997, Determination of Chemical Composition, State of Order, Molar Volume, and Density of a Monoclinic Alkali Feldspar Using X-ray Diffraction, in: Brady, J., Mogk, D., and Perkins D. (eds.) Teaching Mineralogy, Mineralogical Society of America, p. 107-118.
Brady, John B., 1997, Making Solid Solutions with Alkali Halides (and Breaking Them) , in: Brady, J., Mogk, D., and Perkins D. (eds.) Teaching Mineralogy, Mineralogical Society of America, p. 91-95.
Perkins, Dexter, III, and Sorensen, Paul, Mineral Synthesis and X-ray Diffraction Experiments, in: Brady, J., Mogk, D., and Perkins D. (eds.) Teaching Mineralogy, Mineralogical Society of America, p. 81-90.
Hollecher, Kurt, A Long-Term Mineralogy Practical Exam, in: Brady, J., Mogk, D., and Perkins D. (eds.) Teaching Mineralogy, Mineralogical Society of America, p. 43-46.
Moecher, David, 2004, Characterization and Identification of Mineral Unknowns: A Mineralogy Term Project, Jour. Geoscience Education, v 52 #1, p. 5-9.
Hluchy, M.M., 1999, The Value of Teaching X-ray Techniques and Clay Mineralogy to Undergraduates, Jour. Geoscience Education, v. 47, p. 236-240.
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