The present invention provides a method for obtaining a specifically-shaped crystal (specifically, spherocrystal) of a compound with good reproducibility. This method for producing a specifically-shaped crystal (specifically spherocrystal) of a compound comprises: (1) a step for preparing a supersaturated solution of a compound having a degree of supersaturation equal to or higher than a critical degree of supersaturation; and (2) a step for precipitating a specifically-shaped crystal (specifically spherocrystal) of a compound from the supersaturated solution.

To provide a molded article which can have excellent strength, can also have high durability during repeated use, and can maintain high adsorption performance even when the content of a binder resin is reduced. A molded article containing cerium oxide particles and a binder resin, wherein cerium oxide particles which has an average particle diameter of 1 to 15 μm and in each of which a crystallite size is 40 to 200 Å are used.

An aqueous solution containing ions of one or more rare earth elements selected from the group consisting of Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, hydrogen peroxide, urea, and polyvinylpyrrolidone is heated at a temperature of 80° C. or higher and equal to or lower than a boiling point of the aqueous solution to produce particles of a rare earth compound under a reaction between a hydrolysis product of urea and the ions of the rare earth elements. Furthermore, the particles of the rare earth compound are solid-liquid separated from the aqueous solution, and the obtained solid content is baked at a temperature of 600° C. or higher in an atmosphere containing oxygen to produce rare earth oxide particles.

An aqueous solution containing ions of one or more rare earth elements selected from the group consisting of Y, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, hydrogen peroxide, urea, and polyvinylpyrrolidone is heated at a temperature of 80° C. or higher and equal to or lower than a boiling point of the aqueous solution to produce particles of a rare earth compound under a reaction between a hydrolysis product of urea and the ions of the rare earth elements. Furthermore, the particles of the rare earth compound are solid-liquid separated from the aqueous solution, and the obtained solid content is baked at a temperature of 600° C. or higher in an atmosphere containing oxygen to produce rare earth oxide particles.

This invention provides a method for efficiently separating magnesium and lithium from salt lake brine, and simultaneously preparing high-purity magnesium oxide and battery-grade lithium carbonate. The detailed processing steps are as follows: (1) adding urea into the brine to dissolve, (2) placing the solution into the reactor for hydrothermal reaction, the magnesium ion will precipitate and enter the solid phase; (3) filtering and drying the production to get the magnesium carbonate solid, while the lithium ion remains in the liquid phase; (4) after directly concentration and precipitation, the battery-grade lithium carbonate can be obtained, while the calcination of solid-phase product results in the high-purity magnesium oxide. In this method, urea is used as the precipitant to separate magnesium and lithium in salt lake without introducing any new metal ion, and the brine solution is not diluted. The solid product is white and fluffy powder, which is easy to filter and separate. The extraction rate of lithium is high than 94%, and the purity of MgO obtained by calcination is higher than 99.5%.

Embodiments relate to methods for generating selected materials from a natural brine. A natural brine comprising at least a portion of a selected material is heated. CO.sub.2 is added and mixes with the natural brine forming a mixture such that the CO.sub.2/P is a first predetermined value. The mixture is held so that impurities in the natural brine precipitate as solids leaving a second brine substantially comprising the selected material. The second brine is heated. CO.sub.2 gas is injected into the second brine, mixing so that the CO.sub.2/P is a second predetermined value. The mixture is held so that the selected material precipitates out and are removed.

The invention relates to a system and a method for the processing of minerals containing the lanthanide series and the production of rare earth oxides, which allow a completely closed and continuous treatment of the different materials and desorbent agents involved in the process, thus improving the efficiency in the extraction and avoiding environmental risks associated. The method comprising the steps of: reception and conditioning of the raw material; desorption of valuable product through a plurality of mixing and reaction stages in which the raw material is contacted in countercurrent with a stream of desorbent solution; separation of fine solids; precipitation of secondary minerals through the use of a first reactive solution; precipitation of rare earth carbonates through the use of a second reactive solution; and drying and roasting of the rare earth carbonates to obtain rare earth oxides; wherein the method further comprises a secondary process that allows further processing of the residual mineral, and a dewatering and washing step wherein the residual mineral from the desorption step is washed and a lanthanide-containing liquid is recovered.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.

A gas sensor capable of detecting carbon dioxide and having high stability is provided. A carbon dioxide gas sensor comprising an insulating substrate 3 and a gas sensing layer 1 formed on one major surface of the insulating substrate 3 via electrodes 2, wherein the gas sensing layer 1 comprises: (a) one or more rare earth metal oxycarbonates represented by Ln.sub.2O.sub.2CO.sub.3, Ln being at least one rare earth metal element selected from Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Pr, Yb and Lu, the rare earth metal oxycarbonate containing a hexagonal rare earth metal oxycarbonate as a main component; or (b) monoclinic samarium dioxycarbonate,
a production method of the gas sensor, and a method of selectively producing crystal polymorphism of lanthanum dioxycarbonate represented by La.sub.2O.sub.2CO.sub.3 are provided.

The disclosure provides, inter alia, formulations comprising cerium (III) carbonate, and processes for producing cerium (III) carbonate. In embodiments, the disclosure provides methods for passivating photodegradation of organic compounds using cerium (III) carbonate.