CN111411226B - Method for removing calcium ions in rare earth sulfate extraction separation process - Google Patents

Abstract

The invention discloses a method for removing calcium ions in a sulfuric acid rare earth extraction separation process, and belongs to the field of hydrometallurgy. The method for reducing calcium ions in rare earth feed liquid by utilizing calcium sulfate crystal seed induced crystallization is characterized by carrying out oil separation treatment on a high-calcium rare earth sulfate solution in an extraction production line, adding calcium sulfate active crystal seeds according to the solid-liquid ratio (wt.%) of 3-20%, reacting for 0.5-2.0h, aging for 0.5-2.0h, separating solid from liquid, discarding filter residues, realizing in-vitro calcium reduction, adding low-calcium wastewater into a water phase of the rare earth sulfate solution after calcium reduction, and further diluting the rare earth sulfate solution to below the calcium ion saturation solubility to effectively reduce the crystallization in the extraction production line.

Description

Method for removing calcium ions in rare earth sulfate extraction separation process

Technical Field

The invention belongs to the field of wet metallurgy, and particularly relates to a method for removing calcium ions in a rare earth sulfate extraction separation process.

Background

Calcium sulfate crystallization harm is serious in the hydrometallurgical process, for Baotou mixed rare earth ore with the largest reserves in the world, the common separation process is the third-generation sulfuric acid method patent technology smelting independently developed by Beijing non-ferrous metal research institute, Baotou rare earth concentrate is roasted by concentrated sulfuric acid, soaked in water and neutralized, calcium mainly precipitates into waste residues in the form of calcium sulfate, and a small part of calcium is dissolved into sulfuric acid rare earth solution in the form of calcium sulfate and is in a supersaturated state. In the process of rare earth sulfate extraction transformation, in order to avoid the generation of rare earth sulfate double salt, magnesium soap is usually adopted to saponify an organic phase to improve the extraction capacity, impurity calcium ions are introduced, in an extraction separation system, the calcium ions are combined with sulfate radicals in a solution to generate calcium sulfate crystals, the calcium sulfate crystals are easily uncontrollably crystallized and separated out in an extraction production line box body and a pipeline, the two-phase circulation and the extraction level efficiency are influenced, a great deal of harm is brought to the production process, the production efficiency is reduced, the production energy consumption, the economic cost, the labor cost and the like are increased, and certain influence is brought to the product quality.

In order to solve the bottleneck problem of the industry, research and development of other more economical and effective calcium removal methods in the rare earth extraction separation process are necessary.

The existing calcium removal method mainly comprises the following steps:

mechanical cleaning method: in the process of extracting and separating rare earth, a mechanical cleaning method is generally adopted in the industry. And regularly stopping the post-production organization personnel to clean the precipitated calcium sulfate crystals by manual or mechanical means. Zhengmingting and summarizing the design, construction and production experience of a certain large-scale design project P204 extraction workshop, introducing the problem of calcium sulfate crystallization in the production process and treatment measures adopted, aiming at the characteristic that the initially precipitated CaS 04.2H 20 crystals have good fluidity and are deposited at the bottom of a box body and are not difficult to remove, arranging a special extraction impurity removal groove, enabling the CaS 04.2H 20 crystals precipitated in a clarifying chamber funnel to be discharged in a self-flowing mode at regular time every day, lightening the cleaning workload to a certain extent, prolonging the working time of the clarifying chamber, but causing partial calcium sulfate crystals precipitated in a mixing chamber and a pipeline system to harden and be removed only by manual knocking and shoveling along with the prolonging of time, easily causing damages to the inner walls of pipelines and the box body in the manual cleaning process of electric picks and shovels, causing the roughness rise of the walls and easily causing the crystallization precipitation, the influence degree on the production is further deepened, and the application effect is not obvious. Because the mechanical cleaning process needs to spend a large amount of manpower and material resources, the cost is high, and at the present day that the cost of labor is continuously increased, the economic benefit is low, and the process automation production is not facilitated.

Crystallization method: the method can utilize the property that the solubility of the calcium sulfate is low and is reduced along with the reduction of the temperature, and the lower the temperature, the smaller the crystal adhesion capacity is, to reduce the temperature of the sulfuric acid rare earth solution to a certain degree to separate out calcium sulfate crystals, and regularly clean the separated calcium sulfate to realize the removal and the reduction of the calcium. However, the storage tank is large in storage amount in the material crystallization process, so that the temperature of the material is reduced, a large cooling load needs to be borne, the investment of liquid cooling equipment in the early stage is large, the equipment is blocked after calcium sulfate crystals are separated out, the equipment maintenance and manpower cleaning cost is high, and the calcium reduction effect is very limited.

Solvent extraction method: the method is characterized in that different substances are transferred from one solvent to the other solvent by utilizing different distribution coefficients of the different substances in two mutually insoluble solvents, and calcium and rare earth elements are separated by repeated extraction. The Wangjun and the like research that a solvent extraction method is used for extracting and separating non-rare earth impurity calcium from a sulfuric acid system, light rare earth sulfuric acid rare earth solution after extraction grouping is prepared to 18.0g/L, di- (2-ethylhexyl) phosphoric acid is used as an extractant, the ratio of the solution to the rare earth sulfuric acid rare earth solution is 1: 1, 6-stage countercurrent extraction is carried out, then the balanced loaded organic phase is washed by acid water to remove impurities, the calcium removal effect is obvious, but the preparation process is equivalent to the dilution of calcium ions in the solution, the calcium ions in the rare earth sulfate solution are in a supersaturated state in the actual production process, the content of the rare earth sulfate solution is low, the self stock is large, the volume of a material storage tank after dilution is increased, the process has certain feasibility in theory, but in the actual production process, the process flow and the cost need to be further solved and improved, and more energy needs to be invested for further and deep research.

Ultrasonic treatment, magnetic treatment and the like are also proposed, namely materials are treated by utilizing an ultrasonic strong sound field and a magnetic field, so that calcium ions and sulfate radicals are subjected to a series of changes in physical form and chemical properties and cannot be effectively aggregated to form calcium sulfate crystals, and the aim of reducing calcium is fulfilled.

As described above, although there are many schemes for avoiding or reducing calcium crystallization in the rare earth extraction separation process, it is difficult to effectively prevent and remove calcium sulfate crystallization due to process limitations and defects of various methods, and general rare earth separation enterprises do not adopt special calcium reduction measures.

Disclosure of Invention

The invention aims to provide a method for removing calcium ions in a sulfuric acid rare earth extraction separation process, which is used for solving the problem that calcium sulfate crystals are difficult to effectively prevent and remove in the prior art.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a method for removing calcium ions in the extraction separation process of sulfuric acid rare earth comprises the following steps:

step 1: determining a calcium ion concentration enrichment point of an extraction production line, introducing a high-calcium water phase of an extraction section to an oil separation tank for oil separation, separating floating oil and dispersed oil carried by the water phase under the action of gravity, and reducing the content of petroleum in the water phase from 180ppm of raw water to below 30ppm so as to prevent calcium sulfate crystal seeds from being organically wrapped and losing calcium reduction activity;

step 2: introducing the high-calcium water phase in the oil separation tank into a calcium reduction tank, adding calcium sulfate active seed crystals, and starting stirring reaction;

and step 3: introducing the slurry of the calcium reduction tank into a thickener and then aging to realize solid-liquid separation;

and 4, step 4: introducing the low-calcium clear liquid on the upper layer of the thickener into a buffer tank, and introducing calcium sulfate crystals settled at the bottom of the buffer tank into the thickener for solid-liquid separation; returning the slurry at the bottom of the thickener to a calcium reduction tank to ensure that the solid-to-liquid ratio (wt.%) of the calcium reduction tank is within the range of 3-20%; introducing calcium sulfate crystals precipitated from the bottom slurry of the thickener into a filter pressing system for filter pressing to remove the calcium sulfate crystals, and introducing the clear liquid after calcium reduction into a buffer tank;

and 5: adding low-calcium wastewater into the water phase subjected to calcium reduction in the buffer tank to further dilute the calcium ion concentration to be below the calcium ion saturated concentration, and then returning to the extraction separation system.

Preferably, in the step 2, the calcium sulfate active seed crystal is added according to the solid-to-liquid mass percentage of 3-20% and reacts for 30-120 min.

Further, in the step 2, the calcium sulfate active seed crystal is added according to the proportion that the solid-to-liquid ratio mass percentage is 5%, and the reaction is carried out for 60 min.

Preferably, in the step 3, the aging time of the slurry in the thickener is 30-120 min.

Further, in step 3, the aging time of the slurry in the thickener is 60 min.

Preferably, in the step 5, the low-calcium wastewater is low-calcium saponified wastewater generated by extraction and saponification in the extraction and separation process of the rare earth sulfate, so that the cost of subsequent environmental-friendly wastewater treatment is reduced, and the wastewater recycling is realized.

Compared with the prior art, the invention has the following beneficial effects:

(1) the method provided by the invention has good calcium reduction effect, the reduction amplitude is close to 50%, the calcium sulfate crystallization of an extraction production line is effectively reduced, and the box cleaning times are reduced; after P507 rare earth extraction transformation line, the REO content of the raffinate of the rare earth production line is generally 8-10g/L, the calcium content can reach 2g/L (calculated by Ca0, the same is shown below), the calcium content is at the highest value in the whole smelting separation process, the solution system belongs to a metastable solution of calcium, and the calcium can be reduced to about 1g/L by the treatment method;

(2) according to the method, the calcium ion concentration of the rare earth water phase after calcium reduction is further diluted to be close to or lower than the saturated solubility of calcium sulfate by adding low-calcium saponification wastewater, the measures greatly help the extraction transfer line to avoid calcium crystallization, the cleaning of the extraction line is delayed, the crystallization of calcium sulfate in the box body is slowed down, the extraction mixing and clarification time is ensured, the content of 2# line residual liquid is effectively reduced, and the total extraction yield is improved;

(3) total investment of the project: 412.2784 ten thousand yuan, each time, the box cleaning cost is 11 ten thousand per month, 2 tons of P507 organic, 5 tons of P204 organic and 40 tons of kerosene are supplemented, 5 tons of oxide loss is caused, the box cleaning time is prolonged to 6 months from the original 1 month, the annual cost is 510 ten thousand, the yield is improved by 0.3 percent from the original, the annual benefit is 40 ten thousand, and the investment recovery period is as follows: 412/550 is approximately equal to 0.75 year for 9 months;

(4) according to the invention, calcium sulfate crystal seeds are added for induced crystallization to reduce calcium, the slurry after calcium reduction is subjected to solid-liquid separation through a thickener, clear liquid flows into a buffer tank, and partial concentrated slurry is conveyed through a pump body to realize 'slurry return', so that the solid-liquid ratio of a calcium reduction reaction stirring tank is ensured to be in a reasonable range, redundant slurry is conveyed to a filter press through the pump body to be filtered, filtrate flows back to the buffer tank, and filter cakes are discarded;

(5) aiming at the problem of large water consumption in the extraction and separation process of rare earth elements, the invention uses partial extraction saponification wastewater to dilute the calcium ion concentration in the lanthanum cerium sulfate solution, realizes partial water circulation, reduces the wastewater treatment cost while utilizing water resources, and has obvious environmental protection benefit;

(6) the invention greatly reduces the crystallization degree of calcium sulfate in the extraction production line, has obvious calcium reduction effect, small equipment investment and low process operation cost, effectively implements the project, delays the crystallization degree of the extraction production line, prolongs the cleaning period, and plays an active role in controlling the extraction residual liquid and stably operating the whole transformation and separation integrated linkage extraction line.

(7) The cleaning process of the extraction box is abnormally hard, the extraction box belongs to the overlapping operation of special operations such as entering (limited) space, blind plate plugging, high-altitude operation, temporary power utilization and the like, the working environment is severe, the temperature in the extraction box is over 40 ℃ in winter, the conditions that workers are burnt by dilute sulfuric acid and have high-temperature heatstroke exist in the cleaning process, the cleaning of the extraction box is prolonged from the previous one-time cleaning every month to the current one-time cleaning every three to four months after the project is put into use, the annual workload of the cleaning of the extraction box of a company is effectively reduced, a full working rest period is won for vast cadres, more energy is applied to the production operation and development of the company, the staff conscientiously and the concentration force, and the development of the cadres plays an active role, and the extraction box is a civil engineering.

Drawings

FIG. 1 is a schematic process flow diagram of the present invention;

FIG. 2 is a schematic diagram showing the effect of the addition amount of active calcium sulfate seed crystals on the calcium reduction rate;

FIG. 3 is a graph showing the effect of stirring time on calcium reduction rate;

FIG. 4 is a graph showing the effect of aging time on calcium reduction rate;

FIG. 5 is a schematic diagram showing the effect of reaction temperature on the calcium reduction rate;

FIG. 6 is a graph showing the effect of the calcium ion concentration of the stock solution on the calcium reduction rate.

Detailed Description

The present invention will be further described with reference to the following drawings and examples, which include but are not limited to the following examples.

Example 1

FIG. 1 is a schematic view of the process of the present invention, which comprises the following steps:

step 1: leading the water phase of the high-calcium rare earth sulfate solution with the calcium content of 1.89g/L to an oil separation tank for oil separation at the highest calcium ion concentration enrichment point of the extraction production line, wherein the content of petroleum in the high-calcium water phase is less than 30ppm after the oil separation;

step 2: introducing 100m into calcium reduction groove³Adding 5000kg of calcium sulfate active seed crystal into the high-calcium rare earth sulfate solution after oil removal, starting stirring, and reacting for 60 min;

and step 3: and introducing the slurry of the calcium reduction tank into a thickener, aging for 60min, and analyzing the calcium content in the separated rare earth sulfate solution, wherein the calcium content is 1.23 g/L.

And 4, step 4: and introducing the slurry at the bottom of the thickener into a filter press system for filter pressing, and analyzing the water content in the calcium sulfate slag to be less than or equal to 45 percent.

And 5: and introducing the sulfuric acid rare earth solution clear liquid separated by the thickener into a buffer tank, and introducing the calcium sulfate crystals precipitated at the bottom into the thickener for solid-liquid separation.

And 5: adding 41m into water phase after reducing calcium in buffer tank³The low-calcium wastewater further dilutes the concentration of calcium ions, and the analysis shows that the water phase content of the rare earth sulfate solution is less than or equal to 1.0 g/L.

Example 2

Influence of calcium sulfate active crystal seed addition on calcium reduction effect of lanthanum cerium sulfate solution

Wherein the lanthanum cerium sulfate solution is produced on site in a Gansu rare earth production line, the concentration of the rare earth is 8-10g/L, and the concentration of calcium ions is 2-3 g/L; the calcium sulfate seed crystal is prepared by reacting concentrated sulfuric acid and calcium hydroxide slurry, and the pH value in the reaction process is ensured to be 6-7.

500mL of lanthanum cerium sulfate solution is placed in a 1000mL beaker, calcium sulfate seed crystals with different proportions are weighed and added into the beaker, the mixture is stirred for 1h and is kept stand for 1h, the concentration of calcium ions (measured by calcium oxide) in a supernatant is analyzed, and an experimental result is shown in figure 2, and as can be seen from figure 2, when the active calcium sulfate seed crystals are added, the concentration of the calcium ions in the lanthanum cerium sulfate solution is reduced no matter how much the active calcium sulfate seed crystals are added, which indicates that the adding of the calcium sulfate seed crystals really has the effect of inducing calcium reduction. The influence of the addition of the calcium sulfate seed crystal on the reduction degree of the concentration of calcium ions in the solution is relatively complex, when the solid-to-liquid ratio of the calcium sulfate seed crystal to the lanthanum cerium sulfate solution is more than 5%, the reduction degree of the concentration of the calcium ions in the solution is not obviously influenced by increasing the addition of the calcium sulfate seed crystal, but when the solid-to-liquid ratio of the addition of the calcium sulfate seed crystal is less than 5%, the reduction degree in the lanthanum cerium sulfate solution is also sharply reduced along with the reduction of the addition of the calcium sulfate seed crystal. The calcium sulfate crystallization forming process is a process of converting calcium sulfate in a solution into a calcium sulfate crystallization phase, calcium sulfate is crystallized and separated from a supersaturated lanthanum-cerium sulfate solution, two stages of crystal nucleus formation and crystal growth are needed, whether a crystal nucleus body can be formed and how the crystal nucleus body can be formed are related to the direction of the phase change of a substance, and a new phase can be formed spontaneously only when the phase change driving force is increased to be large enough and the free energy exceeds the energy barrier for forming the crystal nucleus with the critical size. In the test, whether the calcium sulfate seed crystal is added or not, the influence of the addition proportion on the concentration of calcium ions in the lanthanum cerium sulfate solution is very large, the calcium sulfate seed crystal is similar to a catalyst in the nucleation process, the energy barrier of nucleation is reduced, the calcium sulfate seed crystal is a homogeneous nucleation mechanism under the condition that the calcium sulfate seed crystal is not added, although the supersaturation degree of the solution reaches a certain degree, a new phase cannot be formed in a certain time, a stable calcium sulfate crystal nucleus can be formed only when the energy barrier of nucleation activation is reached (or exceeded), and the concentration of the calcium ions in the lanthanum cerium sulfate solution is stable and unchanged when the calcium sulfate seed crystal is not added. After the calcium sulfate crystal seeds are added, the nucleation mechanism of the calcium sulfate becomes a heterogeneous nucleation mechanism, the added calcium sulfate crystal seeds play a role in catalyzing the formation of crystal nuclei, the nucleation free energy barrier of the calcium sulfate is reduced, the nucleation is easy to carry out, after the calcium sulfate crystal seeds are added, the calcium ion concentration in the lanthanum cerium sulfate solution is rapidly reduced, the surface of the calcium sulfate crystal seeds provides active centers for heterogeneous nucleation and crystal growth, the more the calcium sulfate crystal seeds are added, the more the provided active centers are provided, the more heterogeneous nucleation and crystal growth can be promoted, when the calcium sulfate crystal seeds are reduced to a certain degree, the provided active centers for nucleation and crystal growth are reduced, the crystallization speed is reduced along with reduction of the calcium ion concentration in the solution, and the reduction speed of the calcium ion concentration in the solution is reduced, so that the calcium ion concentration in the solution is rapidly reduced when the solid-to-liquid ratio of the calcium sulfate crystal seeds is less than 5%, in the case that the solid-to-liquid ratio of the calcium sulfate seed crystal is more than 5%, although the adding amount is increased or decreased, the speed and the degree of decrease of the concentration of calcium ions in the solution are not obviously influenced, because although the active centers provided by the calcium sulfate seed crystal are increased when the adding amount of the calcium sulfate seed crystal is increased, the mass transfer speed of the liquid phase reaches a certain limit, the speed of the calcium ions and sulfate ions in the solution transferring to the surface of the calcium sulfate seed crystal is limited, at the moment, the mass transfer is a speed control step for nucleation, and even if more calcium sulfate seed crystals exist, the nucleation speed can not be increased any more. Therefore, when the calcium sulfate seed crystal is changed, the change of the calcium ion concentration in the solution is not very different.

Example 3

Influence of stirring reaction time on calcium removal effect of lanthanum cerium sulfate solution

500mL of lanthanum cerium sulfate solution is placed in a 1000mL beaker, 25g of calcium sulfate seed crystal is weighed according to the solid-to-liquid ratio of 5% and added into the beaker, the mixture is stirred for different time, the mixture is kept stand for 1h, the concentration of calcium ions (measured by calcium oxide) in supernatant is analyzed, specific data are shown in figure 3, and as can be seen from figure 3, after the calcium sulfate seed crystal is added, the concentration of the calcium ions in the lanthanum cerium sulfate solution is rapidly reduced to a certain degree (within 1 h) and is almost kept unchanged along with the extension of the stirring time. At the start of crystallization, a strong driving force is provided for crystallization due to the greater supersaturation of the system, so that the crystallization at the start proceeds explosively, as observed experimentally in solutions where the calcium ion concentration decreases to lower concentration levels in a shorter time. However, as the crystallization process is carried out, the supersaturation degree of the solution is relatively and rapidly reduced, the driving force of crystallization is correspondingly reduced, and finally, when the supersaturation degree is close, a crystallization equilibrium state is reached, namely the calcium sulfate saturated solution at the temperature, namely, the concentration of calcium ions in the solution is not greatly changed along with the extension of the stirring time after the calcium sulfate seed crystal is added in the experiment. In the reaction process, the reaction time plays an important role, and the length of the reaction time determines the completeness of the reaction and determines the generation amount and the crystal form of calcium sulfate.

Example 4

Influence of aging time on calcium removal effect of lanthanum cerium sulfate solution

500mL of lanthanum cerium sulfate solution is placed in a 1000mL beaker, 25g of calcium sulfate seed crystal is weighed according to the solid-to-liquid ratio of 5% and added into the beaker, the mixture is stirred for 1h and is kept stand for different time, the concentration of calcium ions (in terms of calcium oxide) in the supernatant is analyzed, specific data are shown in figure 4, and as can be seen from figure 4, the concentration of the calcium ions in the lanthanum cerium sulfate solution is rapidly reduced to a certain degree (within 1 h) along with the extension of the aging time and is almost kept unchanged along with the extension of the aging time. At the initial stage of aging, the calcium sulfate crystals in the lanthanum cerium sulfate solution have more small particles, the crystals do not grow, the particles are finer, the solubility is higher, the small particles are in dynamic balance of dissolution and precipitation, the supersaturation degree of the solution is increased by the dissolution of the small particles, and the dissolved calcium ions are precipitated and precipitated on the surface of the large particles of the calcium sulfate crystals along with the extension of the aging time until the concentration of the calcium ions in the calcium sulfate precipitates in the lanthanum cerium sulfate solution is in a metastable state again, so that the growth of the small particles is facilitated in the aging process, and the precipitation and filtration of the calcium sulfate are facilitated.

Example 5

Influence of reaction temperature on calcium removal effect of lanthanum cerium sulfate solution

500mL of lanthanum cerium sulfate solution is placed in a 1000mL beaker, 25g of calcium sulfate seed crystal is weighed according to the solid-to-liquid ratio of 5% and added into the beaker, the mixture is stirred for 1 hour at different reaction temperatures, the mixture is kept stand for 1 hour, the concentration of calcium ions (measured by calcium oxide) in the supernatant is analyzed, the specific data is shown in figure 5, and as can be seen from figure 5, the reduction amplitude of the concentration of the calcium ions in the lanthanum cerium sulfate solution is not changed greatly along with the increase of the reaction temperature. The influence of the temperature on the crystallization process is complex, the temperature is increased, the viscosity and the surface tension of the solution are reduced, the diffusion of ions and the reaction rate are accelerated, the increase of the nucleation rate is facilitated, but the supersaturation degree of the solution is reduced along with the increase of the temperature, and the growth rate of crystals is reduced due to the reduction of the nucleation driving force.

Example 6

Influence of calcium ion concentration of lanthanum-cerium sulfate stock solution on calcium removal effect of lanthanum-cerium sulfate solution

500mL of lanthanum cerium sulfate solution with different calcium ion concentrations is placed in a 1000mL beaker, 25g of calcium sulfate seed crystal is weighed according to the solid-to-liquid ratio of 5% and added into the beaker, the mixture is stirred for 1h and kept stand for 1h, the calcium ion concentration (calcium oxide meter) of the supernatant is analyzed, specific data are shown in figure 6, the data in figure 6 show that the calcium reduction rate in the solution is reduced along with the reduction of the initial calcium ion concentration within a certain range, the supersaturation degree crystallization theory of the solution considers that the supersaturation degree is a key factor influencing the linear growth rate of the crystal and the number density of crystal nucleus particles, the crystallization kinetics considers that the nucleation rate of the crystal is in direct proportion to the n power of the supersaturation degree of the solution, the growth rate of the crystal is also in direct proportion to the m power of the supersaturation degree of the solution, the probability of crystal nucleus formation and the growth rate of the crystal are larger, and the calcium ion concentration is easier to combine with each other to generate calcium sulfate crystal theoretically as the calcium ion concentration is increased, and the faster the crystal growth process. The generation of calcium sulfate crystals is a process of dissolution and re-precipitation, the concentration of calcium ions in feed liquid is a direct reason for the generation of calcium sulfate precipitation crystal nuclei, the length-diameter ratio appearance of the crystals is also greatly influenced, and the solution has enough power to crystallize, nucleate and grow only when the concentration of the calcium ions in the solution reaches a certain value. When the calcium ion concentration in the solution is lower than the saturation concentration, the added calcium sulfate crystal seeds are dissolved until the calcium ion concentration in the solution is saturated again.

The optimal process conditions for the crystal seed method induced calcium reduction of the lanthanum-cerium sulfate solution are as follows: the adding amount of the calcium sulfate seed crystal is 5 percent, the stirring time is 1 hour, and the aging time is 1 hour. The higher the calcium ion concentration is, the more obvious the calcium reduction effect is, the more calcium sulfate crystal seeds are precipitated in vitro, and the final calcium reduction rate can reach more than 50%. When the calcium content is lower than the saturated concentration of lanthanum cerium sulfate, the calcium sulfate crystal seed is dissolved until the solution is saturated again, so the saponified wastewater is introduced into a feed inlet of an extraction line from a calcium-reduced lanthanum cerium sulfate storage tank and is supplemented, the calcium ion of the lanthanum cerium sulfate solution is lower than the saturated concentration, and the calcium sulfate crystal precipitated on the extraction line can be partially dissolved; the stirring intensity has no obvious influence on the calcium reduction effect, but the slurry must be uniformly stirred to provide uniform saturation for the reaction; the reaction temperature has no obvious influence on the calcium reduction effect, and the method can meet the actual production conditions, and the current project is already in test operation, so that the effect is obvious.

The above-mentioned embodiment is only one of the preferred embodiments of the present invention, and should not be used to limit the scope of the present invention, but all the insubstantial modifications or changes made within the spirit and scope of the main design of the present invention, which still solve the technical problems consistent with the present invention, should be included in the scope of the present invention.

Claims (2)

1. A method for removing calcium ions in the extraction separation process of sulfuric acid rare earth is characterized by comprising the following steps:

step 1: determining a calcium ion concentration enrichment point of an extraction production line, and introducing a high-calcium water phase of an extraction section to an oil separation tank for oil separation;

step 2: introducing the high-calcium water phase in the oil separation tank into a calcium reduction tank, adding calcium sulfate active crystal seeds, starting stirring reaction, adding the calcium sulfate active crystal seeds according to the solid-liquid ratio of 5% by mass, and reacting for 60 min;

and step 3: introducing the slurry of the calcium reduction tank into a thickener and then aging to realize solid-liquid separation, wherein the aging time of the slurry in the thickener is 60 min;

and 4, step 4: introducing the low-calcium clear liquid on the upper layer of the thickener into a buffer tank, and introducing calcium sulfate crystals settled at the bottom of the buffer tank into the thickener for solid-liquid separation; returning the slurry at the bottom of the thickener to a calcium reduction tank; introducing calcium sulfate crystals precipitated from the bottom slurry of the thickener into a filter pressing system for filter pressing to remove the calcium sulfate crystals, and introducing the clear liquid after calcium reduction into a buffer tank;

and 5: adding low-calcium wastewater into the water phase subjected to calcium reduction in the buffer tank to further dilute the calcium ion concentration to be below the calcium ion saturated concentration, and then returning to the extraction separation system.

2. The method of claim 1, wherein in step 5, the low-calcium wastewater is low-calcium saponified wastewater generated by extraction saponification in the rare earth sulfate extraction separation process.

Images