Recovery of rare earth elements and compounds from coal ash
Rare earth elements are recovered from coal ash. The coal ash with rare earth elements can be treated with a mineral acid to form an aqueous mineral acid solution. The aqueous mineral acid solution can be extracted to form an organic solution that includes the rare earth salts. The organic solution can be mixed with water to form an aqueous solution that includes the rare earth salts. The rare earth elements are separated from the aqueous solution.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of and priority to U.S. provisional patent application no. 61/625,292, filed Apr. 17, 2012, the entire contents of which are incorporated by reference herein and owned by the assignee of the instant application.
FIELD OF THE INVENTION
The invention relates generally to recovery of rare earth elements and/or compounds from coal ash.
Rare earth elements can be fundamental to emerging green energy technologies in the United States (e.g., permanent magnet motors for wind turbines and disk drives, hybrid car batteries, compact fluorescent lighting, and/or displays in all types of consumer/defense electronics), as well as other usages such as industrial catalysts for refining heavier crude oil, automobile catalytic converters, and/or as alloying elements. Presently, rare earth elements can be obtained through mining.
Coals from certain regions of the world can be particularly rich in rare earth elements, approaching a total concentration of about 1000 parts-per-million (“ppm”). The combustion of coal in power plants for energy generation concentrates non-volatile minerals in the ash by about ten times, to about 10,000 ppm, or on the order of approximately 1%. Coal ash can be the product of burning coal. Coal ash can be comprised of fly ash and bottom ash. Fly ash can be ash that rises with flue gases. Bottom ash can be ash that is found at the bottom of a furnace. Fly ash can be collected before the flue gases reach chimneys of power plants.
A method to extract rare earth elements from coal is desired. The United States alone produces on the order of 100 million metric tons of fly ash annually. Accounting for process yield and variability in rare earth element content, if rare earth elements are extracted from coal ash, a reasonable fraction of currently available fly ash (e.g., about 10-15%) can be adequate to meet rare earth elements demand in the United States.
SUMMARY OF THE INVENTION
Advantages of the invention include recovering rare earth elements from coal ash. Another advantage of the invention includes economical production of rare earth elements and/or compounds from alternative, non-mineral raw materials. Another advantage of the invention is the ability to build reliable production capabilities and/or supply chain for rare earth elements and/or byproducts. Another advantage of the invention is processing fly ash to recover rare earth materials, particularly heavier rare earths, more economically and energy-efficiently per kilogram of rare earth elements than from processing and extracting mineral resources. Another advantage includes the beneficiation of coal ash, which is an abundant waste material, for recovering economically useful and marketable industrial materials that include rare earth elements as a significant component. Another advantage includes energy efficient extraction of rare earth elements, which can save energy use by about 75% relative to conventional mining per unit weight of rare earth elements produced. Yet another advantage is the accompanying carbon dioxide (CO2) emission can be lower than mining by about 75%. Still another advantage includes production of environmentally beneficiated ash cake, which can be free of hazardous elements.
In one aspect, the invention involves a method of recovering rare earth elements from coal ash. The method involves treating coal ash that contains rare earth elements with a mineral acid to form an aqueous mineral acid solution. The aqueous mineral acid solution is extracted to form an organic solution that includes the rare earth salts. The organic solution is mixed with water to form an aqueous solution that includes the rare earth salts. The rare earth elements are recovered by separating the rare earth elements from the aqueous solution.
The aspect described above can include one or more of the following features. In some embodiments, the mineral acid is nitric acid. In various embodiments, treating coal ash can include heating the mineral acid to approximately 90° C. and exposing the coal ash to the mineral acid for at least one hour. Exposing the coal ash can also include additional heating of a resulting solution formed when exposing the coal ash to the mineral acid in order to generate a more concentrated mixture.
In various embodiments, extracting the aqueous mineral acid solution includes mixing aqueous mineral acid solution with tributyl phosphate and kerosene and removing the organic solution from the aqueous mineral acid solution such that the rare earth salts are substantially removed along with the organic solution
In some embodiments, extracting the aqueous mineral acid solution can be done by performing a dry extraction, a liquid extraction, or combination of dry and liquid extraction. In various embodiments, the dry extraction is done by performing continuous extraction of rare earth salts with tributyl phosphate. The dry extraction can be a Soxhlet extraction. In various embodiments, the dry extraction can include diluting the organic solution with kerosene.
The liquid extraction can include mixing a volume of tributyl phosphate and kerosene equal to a volume of the aqueous mineral acid solution and removing the organic solution from the aqueous mineral acid solution. In some embodiments, the liquid extraction can include mixing a volume of tributyl phosphate and kerosene that is a predetermined amount greater than a volume of the aqueous mineral acid solution and removing the organic solution from the aqueous mineral acid solution. The predetermined amount can be 9 times the volume of the aqueous mineral acid solution.
In some embodiments, mixing the organic solution includes performing multiple cycles of mixing the organic solution with water until a concentration level of rare earth salts in the aqueous solution is below a predetermined threshold.
In various embodiments, separating the rare earth elements can include ion exchange. Ion exchange can either be anion exchange or cation exchange. In some embodiments ion exchange separation results in rare earth element mixtures. The rare earth element mixtures can be suitable to be converted to mixtures of rare earth oxides and rare metals for various applications such as catalyst, magnets, and phosphor applications.
In some embodiments, the coal ash can be exposed to a magnetic treatment such that the coal ash separates into a substantially magnetic portion and a substantially non-magnetic portion of the coal ash.
In various embodiments, extracting the aqueous mineral acid solution forms a second aqueous mineral acid solution. The second aqueous mineral acid solution can be distilled to recover mineral acid.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating the principles of the invention by way of example only.
Process for extraction of rare earth elements
A process for the extraction of rare earth elements, including yttrium, from a rare earth element-bearing ore or concentrate, comprising the steps of leaching the rare earth element-bearing ore or concentrate with a lixiviant of hydrochloric acid and magnesium chloride at atmospheric pressure at a temperature of from 90°C to the boiling point of the solution and at an Eh of at least 200 mV. After a liquid/solids separation step, the solution obtained is subjected to steps for removal of iron and for recovery of rare earth elements. Alternatively, rare earth element-bearing ore or concentrate may be leached with sulphuric acid and liquid obtained subjected to extraction of iron and other impurities. Raffinate obtained may be treated with oxalic acid, the precipitate dissolved in hydrochloric acid and subjected to solvent extraction for rare earth elements or the raffinate may be subjected to solvent extraction for removal of rare earth elements and then stripped with hydrochloric acid.
Rare Earth Metal (at. No. 21, 39, Or 57-71) Patents (Class 423/21.1)
Method of recovering rare earth aluminum and silicon from rare earth-containing aluminum-silicon scraps
Patent number: 10280482
Abstract: Disclosed is a method of recovering rare earth, aluminum and silicon from rare earth-containing aluminum-silicon scrap. The method comprises: S1, acid-leaching the rare earth-containing aluminum-silicon scrap with an inorganic acid aqueous solution to obtain a silicon-rich slag and acid leached solution containing rare earth and aluminum element; S2, adding an alkaline substance into the acid leached solution containing the rare earth and aluminum element and controlling a PH value of the acid leaching solution between 3.5 to 5.2, performing a solid-liquid separation to obtain a aluminum hydroxide-containing precipitate and a rare earth-containing solution filter; S3, reacting the aluminum hydroxide containing precipitate with sodium hydroxide to obtain sodium metaaluminate solution and aluminum-silicon slag, and preparing a rare earth compound product with the rare earth-containing filtrate.
Filed: June 16, 2016
Date of Patent: May 7, 2019
Assignee: GRIREM ADVANCED MATERIALS CO., LTD.
Inventors: Xiaowei Huang, Yang Xu, Jinyu Wang, Liangshi Wang, Zongyu Feng, Dali Cui, Zhiqi Long, Xu Sun, Na Zhao
Method for recovering scandium
Patent number: 10156002
Abstract: Provided is a method for recovering scandium with which scandium can be efficiently recovered as high purity scandium oxide from a scandium-containing solution containing impurities such as iron without causing problems such as increased cost and safety problems. According to the method for recovering scandium according to the present invention, the pH of a solution containing scandium and iron (scandium-containing solution) is adjusted within the range of not less than ?0.5 and less than 1, then scandium oxalate is obtained by adding the pH adjusted solution to an oxalic acid solution, and the scandium oxalate is roasted into scandium oxide.
Filed: December 8, 2015
Date of Patent: December 18, 2018
Assignee: SUMITOMO METAL MINING CO., LTD.
Inventors: Ryoma Yamaguma, Tatsuya Higaki, Hidemasa Nagai, Satoshi Asano, Hiroshi Kobayashi
Methods and apparatus for processing of rare earth metal ore
In one aspect, the present invention is directed to methods for extracting rare earth metals from ores comprising reduction of rare earth metal oxyfluorides. In another aspect, the invention relates to an apparatus for extracting rare earth metals from ores comprising reduction of rare earth metal oxyfluorides. The methods and apparatuses described herein generate rare earth metals from ores with reduced requisite pre-removal of metal oxides found as natural impurities in ores.