RU2245845C2 - Method of preparing high-dispersity and granulometrically uniform rare-earth element carbonates with plate or dendritic form - Google Patents

Abstract

FIELD: nonferrous metallurgy.

SUBSTANCE: invention relates to hydrometallurgy of rare-earth elements, in particular to technology of preparing of rare-earth element carbonates with controlled particular shape used in manufacture of polishing materials and catalysts. Suspension of rare-earth element carbonates prepared by mixing rare-earth element carbonate solution with carbonic acid solution is stirred at 20 to 75^оС at suspension motion velocity between 0.5 and 20 m/s, whereupon rare-earth element carbonates are precipitate in plate form at stirring for a period of time satisfying relationship 1.5*T^0.5 ≤ τ ≤ 30. Precipitation of dendritic carbonates is accomplished at stirring for a period of time satisfying relationship 10⁶*T^-2.5 ≤ τ ≤ 600, where τ are numeric values of stirring time, min, and T are numeric values of reaction medium temperature, ^оС.

EFFECT: extended temperature range for precipitation of plate- and dendritic-form rare-earth element carbonates and improved granulometric uniformity of product.

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Description

The invention relates to the field of hydrometallurgy of rare-earth elements, in particular to a technology for producing carbonates of rare-earth elements (REE) with an adjustable particle shape used in the production of polishing materials and catalysts.

The granulometric and morphological properties of REE carbonates depend on the conditions of their deposition, for example, on the concentration of REE and precipitant, process temperature, duration and intensity of mixing, order of introduction of reagents, etc. In addition, the particle size distribution of REE carbonates is determined by the hardware design of the process in the form of continuous or periodic deposition.

A known method for the periodic production of finely dispersed cerium carbonates with lamellar particles, comprising rapidly adding a solution of ammonium carbonate to an intensively mixed solution of cerium nitrate to form a suspension of cerium carbonate, mixing the suspension for 5 minutes at room temperature and a stirrer speed of 400 rpm, unloading the suspension , filtration, washing and drying of cerium carbonate [Protsenko TP Obtaining cerium (IV) oxide with a high specific surface: Author. dis. Cand. tech. sciences. - M., 2000. - 16 p.].

The disadvantage of this method is to obtain carbonates in the form of plates that are heterogeneous in shape and size and the low productivity of the process due to its periodicity.

Closest to the claimed method is the continuous production of highly dispersed REE carbonates with lamellar and needle-shaped particles [Ivanov EN, Mikhaylichenko AI, Karmannikov VP Physico-chemical fundamentals and technology for producing rare-earth polishing powders. // Non-ferrous metals. - 1991. - No. 11. - p. 49-51]. The method includes continuously mixing a solution of REE chlorides with a solution of sodium carbonate with the formation of a suspension of REE carbonates, mixing the suspension while supplying the initial solutions for at least 60 minutes, unloading the suspension, filtering, washing and drying the REE carbonates, with needle-shaped carbonates being obtained at 20 ° C, plate-like at 60 ° C, submicron needle-like at 90 ° C. The speed and duration of mixing the suspension in each case are not indicated.

The disadvantages of this method include the narrow temperature range for producing plate-shaped carbonates, the heterogeneity of plate-shaped carbonates, and the inability to produce dendritic carbonates.

а для получения карбонатов дендритной формы перемешивание проводят в течение времени, отвечающем соотношению

где τ - численные значения времени перемешивания, выраженные в минутах; Т - численные значения температуры реакционной среды, выраженные в градусах Цельсия.A method for producing REE carbonates of plate or dendritic form is proposed, which allows to expand the temperature range for the production of carbonates of one form or another, as well as to improve the particle size uniformity of the product. To this end, in a method comprising continuously feeding and mixing a solution of REE salt and a solution of a carbonic acid salt to obtain a suspension of REE carbonates, mixing the suspension while supplying the initial solutions, unloading, filtering, washing and drying the precipitate of REE carbonates, the suspension is mixed at a temperature of 20 to 75 ° C and a suspension speed of 0.5 to 20 m / s. To obtain plate-shaped carbonates, mixing is carried out for a time corresponding to the ratio

and to obtain carbonates of the dendritic form, mixing is carried out for a time corresponding to the ratio

where τ is the numerical values of the mixing time, expressed in minutes; T - numerical values of the temperature of the reaction medium, expressed in degrees Celsius.

The essence of the method lies in the fact that intensive mixing of a suspension of REE carbonates in the claimed modes leads to a change in the shape of particles from lamellar to dendritic. The intensity and duration of mixing are the main factors affecting the shape of the particles. With intensive, but short-term mixing, large aggregate particles in the form of inhomogeneous plates are obtained. An increase in the duration of mixing contributes to the destruction of aggregate particles into small and granulometrically uniform plates. Intensive and prolonged mixing leads to deformation (stretching) of small lamellar particles and a change in their shape to needle-shaped and then dendritic.

In order to obtain finely dispersed granulometrically homogeneous lamellar or dendritic carbonates, the intensity and duration of mixing should be within the above limits.

At a suspension movement speed of less than 0.5 m / s, local supersaturations and the formation of granulometrically inhomogeneous particles and agglomerates may occur, but dendrites cannot be formed, since particle deformation does not occur with a low pressure of a moving fluid. An increase in the mixing speed above 20 m / s leads to an unjustified increase in power costs, which are not compensated by the achieved result.

The duration of mixing required to change the shape of the particles depends on the temperature of the reaction medium. Therefore, the mixing duration parameter acquires the character of temperature dependence τ = φ (Т). With a mixing duration of τ <1.5 * T ^0.5 , particles are formed in the form of very large (up to 100 μm) and inhomogeneous plates. When mixing for more than 30 minutes, the lamellar particles change shape to a needle-shaped, which persists for a time of 30 <τ <10 ^{6 *} T ^2.5 . With stirring for more than 600 minutes, carbonates are mechanically destroyed and their particle size uniformity is broken.

A decrease in the temperature of the reaction medium below 20 ° C impedes the rearrangement of the plates into dendrites, since the deformation of particles sharply slows down at low temperatures. An increase in temperature above 75 ° C leads to an undesirable change in the shape of particles to a submicron rounded due to the hydrolysis of carbonates.

The claimed method for producing REE carbonates of plate or dendritic form can be implemented in a device consisting of a mixing reactor and a settling chamber. Such a mixer-settler makes it possible to combine the processes of mixing and delamination of the suspension in one apparatus. In addition, the use of a settling chamber makes it possible to keep REE carbonates under the mother liquor in a state of relative rest for a long time, which helps to improve the internal structure of carbonates without changing their shape. Instead of a sludge chamber, an additional mixing reactor can be used, in which the speed of the suspension does not exceed 0.5 m / s.

Ready REE carbonates are separated from the mother liquor, washed and dried. Plate-shaped carbonates have a length of 7 to 20 μm and a width of 3 to 1 μm, and dendritic carbonates have a length of 15 to 20 μm and teeth of 3 to 5 μm, the particle length increasing in the above ranges with increasing intensity and duration of mixing . Lamellar carbonates are used in the production of polishing materials, dendritic carbonates are used in the manufacture of catalysts.

Example No. 1.

Continuous deposition of plate-shaped carbonates is carried out in the device shown in figure 1, where the following designations of the constituent elements are used: 1 - reactor; 2 - settling chamber; 3 - diffuser; 4 - mixer; 5 - dispenser for input of the initial solution of REE; 6 - dispenser for introducing a precipitant solution; 7 - discharge device for the output of REE carbonates; 8 - fitting for the withdrawal of the mother liquor.

Образовавшаяся суспензия переливается через верхний край реактора 1 и по зазору между стенками реактора 1 и диффузора 3 поступает в отстойную камеру 2. В отстойной камере 2 суспензия расслаивается. Осадок карбонатов оседает на дно и выводится через разгрузочное устройство 7, расположенное в днище отстойной камеры 2. Водная фаза осветляется и сливается через штуцер 8 в верхней части отстойной камеры 2. Вывод сгущенной суспензии карбонатов через разгрузочное устройство 7 начинают через 120 минут после начала осаждения, что обеспечивает пребывание карбонатов в отстойной камере 2 в течение 120 минут.The reactor 1 is located inside the settling chamber 2. The volume of the reactor 1 is 0.1 l, settling chamber 2 - 12 l. The reactor 1 is separated from the settling chamber 2 by a diffuser 3. In the reactor 1, a mechanical propeller stirrer 4 is installed with a diameter of 0.02 m, rotating at a speed of 1200 rpm. The maximum speed of the suspension in the reactor 1, equal to the peripheral speed of rotation of the stirrer 4, is 1.2 m / s. The temperature of the reaction medium in the reactor 1 and the settling chamber 2 is 20 ° C. A REE chloride solution containing 100 g / L REE and a precipitant solution containing 95 g / L Na ₂ CO ₃ are fed through dispensers 5 and 6 to reactor 1 at a rate of 0.008 L / min. As a result of mixing the solutions, a suspension of carbonates is formed, which remains in the reactor 1 for 7 minutes. In this case, the inequality

The resulting suspension is poured over the upper edge of the reactor 1 and through the gap between the walls of the reactor 1 and the diffuser 3 enters the settling chamber 2. In the settling chamber 2, the suspension is delaminated. The carbonate precipitate settles to the bottom and is discharged through the discharge device 7 located at the bottom of the settling chamber 2. The aqueous phase is clarified and discharged through the nozzle 8 in the upper part of the settling chamber 2. The discharge of the condensed carbonate suspension through the discharge device 7 begins 120 minutes after the deposition begins, which ensures the presence of carbonates in the settling chamber 2 for 120 minutes.

At the exit of the unloading device 7, carbonates with particles in the form of homogeneous plates with a length of 7 μm and a width of 3 μm are obtained.

Thus, the proposed method and device can continuously obtain at 20 ° C granulometrically uniform plate-shaped carbonates, while using the known method, needle-shaped carbonates are obtained.

Example No. 2.

Continuous deposition of carbonates of the dendritic form is carried out in the device depicted in figure 2, where the following designations of the constituent elements are used: 1 - circulation pipe; 2 - settling chamber; 3 - diffuser; 4 - mixer; 5 - a dispenser for introducing an initial REE solution; 6 - a dispenser for introducing a precipitant solution; 7 - discharge device for the output of REE carbonates, 8 - fitting for the withdrawal of the mother liquor.

The device consists of a circulation pipe 1 located inside the settling chamber 2. The volume of the circulation pipe 1 is 0.05 l, settling chamber 2 - 3 l. The circulation pipe 1 is separated from the settling chamber 2 by a diffuser 3. A mechanical propeller 4 mixer with a diameter of 0.02 m is installed in the circulation pipe 1, rotating at a speed of 1200 rpm and creating an upward flow of liquid. The maximum speed of the suspension in the circulation pipe I, equal to the peripheral speed of rotation of the mixer, is 1.2 m / s. The temperature of the reaction medium throughout the device is 60 ° C. A hot REE chloride solution containing 100 g / L REE and a precipitant solution containing 95 g / L Na ₂ CO ₃ are fed through dispensers 5 and 6 to circulation pipe 1 at a rate of 0.0015 l / min. As a result of mixing the solutions, a suspension of REE carbonates is formed, which is poured over the upper edge of the circulation pipe 1 and, through the gap between the circulation pipe 1 and the diffuser 3, enters the settling chamber 2. In the settling chamber 2, the suspension delaminates. The carbonate precipitate settles to the bottom and is discharged through a discharge device 7 located at the bottom of the settling chamber 2. Part of the precipitate is returned from the settling chamber 2 to the circulation pipe 1 due to the pumping action of the mixer 4. In the settling chamber 2, the aqueous phase is clarified and discharged through the nozzle 8. Conclusion carbonates through the discharge device 7 begin after 180 minutes after deposition, which ensures the presence of carbonates in the mixing zone for 180 minutes. In this case, the condition

At the outlet of the unloading device 7, carbonates with dendritic particles are obtained, the primary dendrite needle having a length of 15-20 μm, and the secondary needles (teeth) of 3-5 microns in size.

Thus, the proposed method and device can continuously produce dendritic carbonates at 60 ° C, while using the known method carbonates are obtained in the form of plates.

Claims (3)

1. A method of producing highly dispersed granulometrically uniform REE carbonates of plate or dendritic form, comprising continuously feeding and mixing a REE salt solution and a carbonic acid salt solution to obtain a REE carbonate suspension, mixing the suspension while supplying the initial solutions, continuously unloading, filtering, washing and drying the precipitate REE carbonates, characterized in that the mixing is carried out at a temperature of from 20 to 75 ° C and a speed of movement of the suspension from 0.5 to 20 m / s. 2. The method according to claim 1, characterized in that to obtain carbonates with lamellar particles, mixing is carried out for a time corresponding to the ratio

where τ is the mixing time, min, T is the temperature of the reaction medium, ° C. 3. The method according to claim 1, characterized in that to obtain carbonates with particles of a dendritic form, mixing is carried out for a time corresponding to the ratio

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