Method and system for purifying magnesium sulfate solution

Abstract

The invention discloses a method and a system for purifying a magnesium sulfate solution. The method comprises the following steps: pretreating a magnesium sulfate solution containing nickel and cobalt impurities to remove suspended matters and organic matters in the magnesium sulfate solution; adding sodium hydrosulfide into the pretreated magnesium sulfate solution, enabling nickel and cobalt to respectively react with the sodium hydrosulfide to generate precipitates, and carrying out solid-liquid separation to obtain the purified magnesium sulfate solution and precipitates containing nickel sulfide and cobalt sulfide; evaporating and crystallizing the purified magnesium sulfate solution to obtain magnesium sulfate crystals, and drying to obtain a magnesium sulfate product; and carrying out post-treatment on the precipitate containing the nickel sulfide and the cobalt sulfide, and recovering nickel and cobalt in the precipitate. The method can efficiently remove nickel and cobalt impurities in the magnesium sulfate solution, has the advantages of high efficiency, environmental protection, recoverable resources and the like, and can reduce the production cost and improve the resource utilization rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a method and system for purifying magnesium sulfate solution. BACKGROUND

[0002] Magnesium sulfate solution is widely used in many industrial fields such as chemical industry, medicine, agriculture, etc. However, it often contains impurities such as nickel and cobalt. For example, magnesium sulfate waste solution produced in the production process of nickel sulfate contains about 50 g / L of magnesium, as well as a certain concentration of cobalt (e.g. <100 mg / L) and nickel (e.g. <100 mg / L) ions. The presence of these impurities can affect the quality of magnesium sulfate and the subsequent application effect. For example, in the medical field, the presence of impurities may affect the safety and effectiveness of drugs; in the electronics industry, the purity of magnesium sulfate solution is extremely high, and impurities may cause product performance to decline. Therefore, it is of great practical significance to purify magnesium sulfate solution to remove nickel and cobalt impurities.

[0003] The traditional purification method of magnesium sulfate solution mainly adopts alkali precipitation method, that is, by adding alkali substances such as sodium hydroxide, nickel and cobalt ions are generated to form hydroxide precipitate. This method has obvious drawbacks: first, the alkali consumption is large, which leads to the increase of production cost; second, a large amount of waste residue is produced, and these waste residues contain heavy metals, which will cause serious environmental pollution if not properly treated; third, the treatment efficiency is low, and it is difficult to remove nickel and cobalt impurities to a high purity requirement, which cannot meet the preparation needs of high-purity magnesium sulfate solution. Ion exchange method has certain advantages, but the cost is high and the equipment requirements are also harsh. Therefore, it is of great significance to develop a high-efficiency, low-cost and environmentally friendly method for purifying magnesium sulfate solution to remove nickel and cobalt impurities.

[0004] In addition, in the experimental study of magnesium sulfate solution purification and impurity removal, Ma Liyan et al. used neutralization and hydrolysis method and sodium carbonate precipitation method to purify magnesium sulfate solution, but they prepared high-purity basic magnesium carbonate, not high-purity magnesium sulfate product. SUMMARY

[0005] According to one embodiment of the present application, the purpose is to provide a method and system for purifying magnesium sulfate solution to solve the problems of large alkali consumption, large amount of waste residue, low treatment efficiency, and difficulty in meeting environmental protection and resource recycling needs existing in the existing purification method of magnesium sulfate solution.

[0006] The above-mentioned purpose can be achieved by the following technical solutions:

[0007] According to one aspect of the present application, the present application provides a method for purifying magnesium sulfate solution, comprising the following steps:

[0008] The magnesium sulfate solution containing nickel and cobalt impurities is pretreated to remove the suspended solids and organic matters therein;

[0009] Sodium hydrosulfide is added to the pretreated magnesium sulfate solution, the pH value of the solution is controlled between 6.5 and 7.5, and the nickel and cobalt are made to react with the sodium hydrosulfide respectively to form precipitates under stirring, so that the purified magnesium sulfate solution and the precipitates containing nickel sulfide and cobalt sulfide are obtained through solid-liquid separation;

[0010] The purified magnesium sulfate solution is subjected to evaporation crystallization to obtain magnesium sulfate crystals, which are then dried to obtain the magnesium sulfate product;

[0011] The precipitates containing nickel sulfide and cobalt sulfide are subjected to post-treatment to recover the nickel and cobalt therein.

[0012] Optionally, in the step of pretreating the magnesium sulfate solution containing nickel and cobalt impurities, the magnesium sulfate solution is filtered through a quartz sand filter and an activated carbon filter in sequence.

[0013] Optionally, in the quartz sand filter, the particle size of the filter material is 0.5-4 mm, and the porosity is 40%-45%.

[0014] Optionally, in the activated carbon filter, the filter material is coconut shell activated carbon, the particle size is 1.0-2.0 mm, and the filling height is 1000-1500 mm.

[0015] Optionally, when the activated carbon filter is used to filter the magnesium sulfate solution, the flow rate is controlled at 1-2 m / h.

[0016] Optionally, in the activated carbon filter, the coconut shell activated carbon is an activated carbon after alkaline treatment.

[0017] Optionally, the amount of sodium hydrosulfide added is 1.5-2.5 times the theoretical equivalent of the total content of nickel and cobalt in the magnesium sulfate solution.

[0018] Optionally, in the step of making the nickel and cobalt react with the sodium hydrosulfide respectively to form precipitates under stirring, the reaction temperature is 20-50℃, the stirring speed is 100-300 r / min, and the reaction time is 0.5-2 hours.

[0019] Optionally, the magnesium sulfate product is a high-purity magnesium sulfate product.

[0020] Optionally, the temperature for evaporation crystallization is controlled at 50-70℃, and the temperature for drying treatment is controlled at 60-100℃.

[0021] Optionally, before the step of subjecting the purified magnesium sulfate solution to evaporation crystallization, the purified magnesium sulfate solution is subjected to detection to ensure that the content of nickel and cobalt is lower than 1.0 mg / L.

[0022] Optionally, the precipitate containing nickel sulfide and cobalt sulfide is treated by acid leaching method to recover nickel and cobalt therein; wherein, the acid ore ratio is 500-900 kg / t, the stirring time is 1-3 h, the liquid-solid ratio is 4-8:1, the temperature is 80-95 ℃, and the stirring speed is 300-800 r / min.

[0023] Optionally, while adding sodium hydrosulfide to the pretreated magnesium sulfate solution, an auxiliary reagent is added, and the auxiliary reagent is one or more selected from surfactants and complexing agents.

[0024] According to one aspect of the present application, the present application provides a system for purifying a magnesium sulfate solution, the system comprising:

[0025] a pretreatment unit for pretreating the magnesium sulfate solution containing nickel and cobalt impurities to remove suspended solids and organic matter therein;

[0026] a sodium hydrosulfide purification unit for adding sodium hydrosulfide to the pretreated magnesium sulfate solution, controlling the pH value of the solution to be between 6.5 and 7.5, and stirring to make nickel and cobalt react with sodium hydrosulfide to form precipitates;

[0027] a precipitate separation unit for performing solid-liquid separation on the material obtained from the sodium hydrosulfide purification unit to obtain a purified magnesium sulfate solution and a precipitate containing nickel sulfide and cobalt sulfide;

[0028] a crystallization and drying unit for evaporating and crystallizing the purified magnesium sulfate solution to obtain magnesium sulfate crystals, and then drying the magnesium sulfate crystals to obtain a magnesium sulfate product;

[0029] a post-treatment unit for post-treating the precipitate containing nickel sulfide and cobalt sulfide to recover nickel and cobalt therein.

[0030] Beneficial effects: According to one embodiment of the present application, the method and system for purifying a magnesium sulfate solution can efficiently remove nickel and cobalt impurities in the magnesium sulfate solution, reduce the use of alkali in the conventional precipitation method, reduce the amount of waste residue, realize environmental protection and resource recovery, effectively remove nickel and cobalt impurities in the magnesium sulfate solution, and prepare a high-purity magnesium sulfate product to meet the demand of industrial production for high-purity magnesium sulfate.

[0031] Compared with the prior art, some embodiments of the present application have the following advantages:

[0032] 1) Environmentally friendly and efficient: Sodium hydrosulfide is used as a purifying agent, avoiding the use of large amounts of alkali in traditional methods, reducing the generation of waste residue, and reducing the risk of environmental pollution. The generation efficiency of sulfide precipitate is high, which can quickly remove nickel and cobalt impurities, and improve the treatment efficiency. By controlling the pH value within a suitable range, the effective dissociation of sodium hydrosulfide can be ensured, and the generation of hydrogen sulfide gas can be avoided, reducing environmental pollution. Through the synergistic treatment mechanism of pretreatment-sodium hydrosulfide precipitation, nickel and cobalt ions in the magnesium sulfate solution can be effectively removed, and the precipitation efficiency can be improved, i.e., the solution purification efficiency can be improved.

[0033] 2) High-purity product: Through the pretreatment and sodium hydrosulfide purification process, the nickel and cobalt impurities in the magnesium sulfate solution can be removed to a very low level, and a high-purity magnesium sulfate solution (purity ≥ 99.5) can be prepared, meeting the application requirements of high-end industrial fields.

[0034] 3) Process optimization: The entire process flow is designed in an integrated manner, from pretreatment to crystallization and drying, with close connection between each step, simple operation, and realization of industrialized continuous production, improving production efficiency and reducing production cost. In some preferred embodiments, pretreatment is carried out by quartz sand filtration and activated carbon filtration in sequence to remove suspended solids and organic matter; after purification, residue acid leaching post-treatment is carried out to realize the recycling of nickel and cobalt, and the liquid is combined with the evaporation crystallization and drying steps to realize an integrated process from purification to high-purity product preparation, improving production efficiency and forming a complete purification process.

[0035] 2) Resource recovery: The nickel and cobalt sulfide precipitate obtained by precipitation separation can be further treated to realize the recycling of nickel and cobalt, improving resource utilization and reducing production cost. For example, nickel and cobalt metals can be recovered by acid leaching to realize the recycling of resources and improve resource utilization.

[0036] 5) Cost reduction: Compared with some complex ion exchange processes, the sodium hydrosulfide used in the present application has a relatively low price, and the reaction conditions are mild, and the equipment requirements are not high, greatly reducing the treatment cost. At the same time, by controlling the reaction conditions, the excessive use of reagents can be reduced, further saving costs. DETAILED DESCRIPTION

[0037] In order to better illustrate the present application, the technical solutions of the present application are described in detail below. Obviously, the following examples are only a part of the examples of the present application, but not all examples. The following description of at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its applications or uses. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0038] The application provides a method for purifying a magnesium sulfate solution, and a system for purifying a magnesium sulfate solution is used to purify the magnesium sulfate solution, the system comprises a pretreatment unit, a sodium hydrosulfide purification unit, a precipitation separation unit, a crystallization and drying unit and a post-treatment unit, and the method comprises the following steps: pretreating a magnesium sulfate solution containing nickel and cobalt impurities to remove suspended solids and organic matter in the magnesium sulfate solution; adding sodium hydrosulfide to the pretreated magnesium sulfate solution, so that the nickel and the cobalt react with the sodium hydrosulfide to form precipitates, and then the solid-liquid separation is performed to obtain a purified magnesium sulfate solution and a precipitate containing nickel sulfide and cobalt sulfide; performing evaporation crystallization on the purified magnesium sulfate solution to obtain magnesium sulfate crystals, and then performing drying treatment to obtain a magnesium sulfate product; and performing post-treatment on the precipitate containing nickel sulfide and cobalt sulfide to recover the nickel and the cobalt.

[0039] Through the synergistic treatment mechanism of the pretreatment and the sodium hydrosulfide purification, the nickel and the cobalt impurities in the magnesium sulfate solution can be efficiently removed, the purity requirement of the high-purity magnesium sulfate solution is met, and the problems of environmental pollution, high waste residue treatment cost and low treatment efficiency caused by the large use of alkali in the prior art are solved. The method has the advantages of high efficiency, environmental protection, resource recycling and the like, can reduce the production cost, improve the resource utilization rate, and has a wide application prospect. The above method is suitable for the purification treatment of various magnesium sulfate solutions containing nickel and cobalt impurities, for example, magnesium sulfate waste liquid generated in the production process of nickel sulfate used as a battery raw material. The purified magnesium sulfate solution meets the quality requirement of the high-purity magnesium sulfate product, the evaporation crystallization obtains high-purity magnesium sulfate crystals, and the drying treatment obtains a high-purity magnesium sulfate product, and the method is particularly suitable for the industrial production process of the high-purity magnesium sulfate. In addition, by optimizing the process parameters of each step, the purification efficiency and the product quality can be further improved, and the specific content will be described in detail in the following examples.

[0040] In the application, the magnesium sulfate solution is pretreated before the sodium hydrosulfide purification. For example, a quartz sand filter, an activated carbon filter, an ultrafiltration membrane filter, a microfiltration membrane filter or the like is used to remove suspended solids, organic matter and other impurities in the magnesium sulfate solution, so as to provide good water inlet conditions for the subsequent purification treatment.

[0041] In some preferred embodiments, the magnesium sulfate solution is pretreated by using a quartz sand filter and an activated carbon filter in sequence. Through physical filtration and adsorption, impurities such as suspended solids and organic matter in the magnesium sulfate solution can be effectively removed, avoiding the influence of these impurities on the subsequent purification reaction, and providing a clean solution environment for the sodium hydrosulfide purification step. The inventors of the present application have analyzed the magnesium sulfate solution and the existing form of nickel and cobalt in it in depth, and have realized that the magnesium sulfate solution (especially obtained from salt lake brine, seawater magnesium extraction or industrial by-products) may contain two types of key impurities, namely mechanical impurities and organic / polar impurities. Among them, the mechanical impurities, such as undissolved Mg(OH)2 particles, silicate colloids, ore debris, etc., these solid particle residues will hinder the crystallization of sulfides (NiS / CoS) (form colloidal suspensions). The organic / polar impurities, such as humic acid, surfactant residues, organic ligands complexing nickel and cobalt, etc., the presence of these impurities will complex nickel and cobalt ions, and if the nickel and cobalt ions are complexed, it is difficult to directly precipitate by sodium hydrosulfide alone, thus reducing the sodium hydrosulfide precipitation efficiency. Based on this, in the preferred embodiments of the present application, the interstitial gaps of quartz sand are used to intercept suspended solids, and the mechanical impurities are removed, and the adsorption of activated carbon is used to adsorb organic / polar impurities in the solution (so that nickel and cobalt mainly exist as free ions Ni 2+ / Co 2+ ), through the above two-stage filtration, the two types of key impurities in the magnesium sulfate solution that affect the precipitation of nickel and cobalt are accurately removed, the solution turbidity is controlled to ≤1 NTU, and a "clean liquid phase environment" is provided for the subsequent precipitation, so that the sulfides are directly precipitated in the crystalline state, avoiding the generation of colloids and the waste of precipitants. In addition, the magnesium sulfate solution is weakly acidic and contains Cl-, the use of quartz sand filter and activated carbon filter can avoid the problems of short service life and easy introduction of Fe 2+ / Cu 2+ etc. impurities in conventional equipment.

[0042] Preferably, in the quartz sand filter, the quartz sand filter material has a micron-level particle size of 0.5-4 mm and a porosity of 40%-45%. By using the filter material with the specific particle size and porosity, particles ≥5 μm are removed, avoiding the blockage of large particles in the subsequent activated carbon pore channels.

[0043] Preferably, in the activated carbon filter, the filter material type is coconut shell activated carbon with high specific surface area, the particle size range is 1.0-2.0 mm, and the filling height is 1000-1500 mm, which can further improve the adsorption effect of organic / polar impurities. Further preferably, a smaller flow rate is used for activated carbon filtration, for example, the flow rate is controlled at 1-2 m / h, thereby prolonging the contact time to sufficiently adsorb the complex impurities. Further preferably, the activated carbon can be subjected to alkaline treatment, for example, modified treatment by soaking with NaOH, etc., to enhance the adsorption of acidic organic ligands. More specifically, when NaOH is used for the modification treatment of activated carbon, 20 wt.% NaOH is used, the mass ratio of activated carbon to NaOH solution is 1:5-1:10, and the soaking time is 12-24 h.

[0044] By optimizing the parameters in the pretreatment steps of the quartz sand filter and the activated carbon filter respectively, the solution turbidity can be further reduced, and the pretreatment effect can be improved.

[0045] Further, the quartz sand filter adopts multi-layer grading, and based on the porosity, the suspended solids retention efficiency can be ≥95%. The bottom layer of coarse sand (as a support layer): 2.0-4.0 mm, thickness 100-150 mm; the middle layer of medium sand (as a filter layer): 0.8-1.2 mm, thickness 500-800 mm; the top layer of fine sand (surface layer filtration): 0.5-0.8 mm, thickness 200-300 mm. The quartz sand filter material type is refined quartz sand, wherein the SiO2 content is ≥99%, the clay content is <0.5%, and there are no impurity particles. Using the above specific quartz sand filter and activated carbon filter for pretreatment, the solution turbidity can be controlled at ≤0.3 NTU, which creates more favorable conditions for subsequent precipitation.

[0046] In the present application, sodium hydrosulfide is used as a purifying agent, and a pretreatment-sodium hydrosulfide precipitation synergistic treatment mechanism is adopted to improve the solution purification efficiency. Compared with other sulfides, sodium hydrosulfide can selectively precipitate nickel and cobalt ions without introducing other impurities, and has the advantages of high selectivity, high safety, and low cost. By using sodium hydrosulfide as a purifying agent, nickel and cobalt are reacted with sodium hydrosulfide to form precipitates, and then solid-liquid separation is performed to purify the magnesium sulfate solution, which avoids the use of a large amount of alkali in the traditional method, reduces the generation of waste residues, and reduces the environmental pollution risk.

[0047] Sodium hydrosulfide purification principle: under weakly acidic to neutral conditions, sodium hydrosulfide dissociates into sulfhydryl ions (HS-), nickel ions (Ni 2+ ) and cobalt ions (Co 2+ ) react with sulfhydryl ions to form nickel sulfide (NiS) and cobalt sulfide (CoS) precipitates, and the reaction equation is as follows:

[0048] Ni2+ + HS - → NiS↓ + H +

[0049] Co 2+ + HS - → CoS↓ + H + .

[0050] The inventors of the present application have found that sodium hydrosulfide (NaHS) dissociates into Na + , HS - in aqueous solution, and HS - can further weakly dissociate into H + and S 2 -, and the release of S 2 - is more controllable; based on this, the inventors have realized selective precipitation, i.e., high-selective removal of nickel and cobalt and retention of magnesium, by controlling the release rate of sulfur ions, avoided the introduction of new impurities, and met the stringent requirements for purification of magnesium sulfate solution.

[0051] In some preferred embodiments, by adjusting the pH of the solution to the range of weakly acidic to neutral, the concentration of S 2 - can be maintained in an interval that can only precipitate nickel and cobalt but not magnesium, based on the dissociation characteristics of sodium hydrosulfide, selective precipitation can be achieved by precise control of pH.

[0052] Preferably, when sodium hydrosulfide is used for purification, the pH value of the solution is controlled to be between 6.5 and 7.5, for example, 6.5, 7.0, 7.5, etc. By controlling the pH value in the above suitable range, the effective dissociation of sodium hydrosulfide can be ensured, and the generation of hydrogen sulfide gas can be avoided, reducing environmental pollution. The inventors of the present application have found that if the pH value is too high, for example, pH > 7.5, the dissociation of HS - is intensified, the concentration of S 2- suddenly increases, leading to the precipitation of Mg 2+ and the loss of magnesium; excessive S 2 - combines with H + to generate HS - , resulting in a decrease in the effective utilization rate of sodium hydrosulfide; the sulfide precipitate is refined into a colloid, making filtration difficult, and the residual amount of nickel and cobalt increases. If the pH value is too low, for example, < 6.5, H2S gas escapes, the concentration of sulfur ions is insufficient, and the removal rate of nickel and cobalt decreases; and under this acidic condition, Ni 2+ / Co 2+ may form complex ions with residual Cl - in the solution, which can inhibit sulfide precipitation; the hydrolysis of Mg 2+ in the magnesium sulfate solution is intensified, and the generated Mg(OH)2 colloid is mixed with the sulfide precipitate, leading to the "encapsulation of mixed crystals" phenomenon in the subsequent crystallization process.

[0053] In some preferred embodiments, based on the dissociation characteristics of sodium hydrosulfide, by controlling the addition amount of NaHS and the reaction pH, the sudden increase of S2 - Excessive concentration leads to Mg 2+ The problem of co-precipitation is solved to further improve the purification efficiency.

[0054] Preferably, when sodium hydrosulfide is used for purification, the amount of sodium hydrosulfide added is 1.5 to 2.5 times the theoretical equivalent of the total content of nickel and cobalt in the magnesium sulfate solution. The inventors of this application have found that excessive sodium hydrosulfide will lead to S 2 Excessive concentrations can cause magnesium precipitation and H2S gas release, while insufficient concentrations can result in incomplete nickel and cobalt removal. A slight excess of sodium hydrosulfide balances reaction kinetics (complete nickel and cobalt precipitation) and selectivity (avoiding magnesium loss). By further optimizing the amount of sodium hydrosulfide added within the aforementioned pH range, the effectively dissociated hydrosulfide ions can completely precipitate the nickel and cobalt ions in the magnesium sulfate solution, improving purification efficiency and product quality. Furthermore, during the raw material preparation stage, a sodium hydrosulfide solution with a concentration of 20-35 wt.% can be prepared for ease of use.

[0055] The inventors of the present application have recognized that the sulfide precipitation process follows "nucleation-growth" kinetics. In some preferred embodiments, the purification efficiency and product quality can be improved by controlling the reaction temperature.

[0056] Preferably, when using sodium hydrosulfide for purification, the reaction temperature is controlled at 20-50°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, etc. Too low a temperature will reduce the reaction rate and form fine colloidal particles that are difficult to filter; too high a temperature may cause H2S to volatilize, affect the stability of magnesium sulfate, and even trigger side reactions.

[0057] Furthermore, the reaction time can be controlled to be 0.5 to 2 hours, for example, 0.5 hour, 1 hour, 1.5 hours, 2 hours, etc. Furthermore, the reaction is carried out in a stirring manner with a stirring speed of 100 to 300 r / min, for example, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, etc.

[0058] In some preferred embodiments of the present invention described above, based on the purification principle of sodium hydrosulfide, further optimization of the reaction method and reaction temperature further improves purification efficiency and product quality. Furthermore, compared to some complex ion exchange processes, the sodium hydrosulfide used in the present invention is relatively inexpensive, and the reaction conditions are mild, requiring minimal equipment, significantly reducing processing costs. Furthermore, by controlling the reaction conditions, excessive use of reagents can be reduced, further saving costs.

[0059] In some preferred embodiments, an auxiliary agent is added at the same time as sodium hydrosulfide is used as the purifying agent, forming a synergistic purifying effect. The auxiliary agent can be one or more selected from surfactants and complexing agents. Surfactants such as polyethylene glycol can promote the agglomeration of sulfide particles and reduce colloidal residues. Complexing agents such as citric acid can preferentially complex magnesium ions, further inhibiting their reaction with S 2 - reaction, enhancing selectivity. It should be noted that the amount of auxiliary agent added is not limited here and can be adjusted according to the above principles. For example, 0.02 g / L to 0.08 g / L of a surfactant or the like can be added at the same time as sodium hydrosulfide is added.

[0060] After the purifying reaction is complete, the density difference between the nickel and cobalt sulfide precipitate and the magnesium sulfate solution can be used to allow the precipitate to settle and accumulate at the bottom by standing. Further, the solution can be allowed to stand for 30 to 60 minutes, for example, 30 minutes, 40 minutes, 50 minutes, 60 minutes, or the like, and then the precipitate can be separated from the solution by solid-liquid separation, such as filtration or centrifugation. The magnesium sulfate solution after removal of nickel and cobalt (i.e., the purified magnesium sulfate solution) and the precipitate containing nickel and cobalt sulfides are obtained after separation. The filtration can use a plate-and-frame filter press or the like, and the centrifugation can use a centrifuge, with the appropriate separation method selected according to the production scale and actual needs. In addition, the solid-liquid separation method can also use air flotation (by introducing gas into the solution, allowing the precipitate to adhere to the gas bubbles and float up) or other solid-liquid separation methods to achieve solid-liquid separation.

[0061] In addition, before evaporation and crystallization, the purified magnesium sulfate solution can be detected to ensure that the nickel and cobalt contents meet the expected standards, for example, to ensure that the contents of cobalt and nickel in the purified magnesium sulfate solution are both less than 1.0 mg / L to meet the needs of subsequent evaporation and crystallization processes.

[0062] In preferred embodiments, when preparing the magnesium sulfate product from the purified magnesium sulfate solution, evaporation and crystallization are performed first, and then drying is performed. Preferably, the temperature of the evaporation and crystallization is controlled at 50 to 70°C, for example, 50°C, 60°C, 70°C, or the like, to avoid high temperatures causing MgSO4·7H2O to lose water (beginning to lose crystallization water at 70°C and above), while inhibiting Na + co-crystallization (Na2SO4 solubility increases significantly with increasing temperature). In addition, the drying temperature can be controlled at 60 to 100°C, for example, 60°C, 80°C, 100°C, or the like. By controlling the evaporation and crystallization conditions, the quality of the magnesium sulfate product is further improved, and the combination of purification and crystallization and drying steps achieves an integrated process from purification to high-purity product preparation, improving production efficiency.

[0063] Further, by using vacuum evaporation method, the boiling point of the solution is reduced, low-temperature evaporation is realized, the crystal hydration structure is protected, and the volatilization of H2S residual gas is reduced. Further, the vacuum degree can be controlled to be -0.08 to -0.09 MPa.

[0064] In the present application, the precipitate containing nickel sulfide and cobalt sulfide obtained by precipitation separation can recover the nickel and cobalt metals therein through further post-treatment, realize the recycling of resources, and improve the resource utilization rate.

[0065] In some preferred embodiments, in the step of post-treating the precipitate containing nickel sulfide and cobalt sulfide, an acid leaching treatment method is used to recover the nickel and cobalt metals therein, realize the recycling of resources, improve the resource utilization rate, and reduce the production cost.

[0066] Further, the acid-ore ratio is 500 to 900 kg / t, for example, 500 kg / t, 600 kg / t, 700 kg / t, 800 kg / t, 900 kg / t, etc., the stirring time is 1 to 3 h, the liquid-solid ratio is 4 to 8:1, for example, 4:1, 5:1, 6:1, 7:1, 8:1, etc., the temperature is 80 to 95℃, for example, 80℃, 85℃, 90℃, 95℃, etc., and the stirring speed is 300 to 800 r / min. By controlling the acid leaching conditions, efficient recovery of nickel and cobalt metals is realized.

[0067] The technical solutions of the present application will be described below in conjunction with the embodiments of the present application,

[0068] Example 1

[0069] The nickel content in the magnesium sulfate solution containing nickel and cobalt impurities is 50 mg / L, and the cobalt content is 30 mg / L.

[0070] First, filtration is performed through a refined quartz sand filter to remove suspended solids and organic matter. In the quartz sand filter, the bottom layer of coarse sand is 3.0 mm thick, the middle layer of medium sand is 1.0 mm thick, and the top layer of fine sand is 0.6 mm thick, so that the porosity is 42% and the suspended solids retention efficiency is 98%. Then, a coconut shell activated carbon filter treated with 20 wt.% NaOH is used for filtration (wherein the wt.% ratio of activated carbon / NaOH solution is 1:8 when the coconut shell activated carbon filter is treated with NaOH, and the soaking time is 12 h), the particle size range is 1.5 mm, the filling height is 1200 mm, and the flow rate is controlled at 2 m / h, to obtain the pretreated solution.

[0071] The pretreated solution is added with sodium hydrosulfide solution with a concentration of 30wt.% and the amount of sodium hydrosulfide added is 2 times the theoretical equivalent of the total content of nickel and cobalt, the pH value of the solution is controlled at 7.0, the reaction temperature is 30℃, the stirring reaction is carried out for 60 minutes, the stirring speed is 200r / min, so that the nickel and cobalt react with sodium hydrosulfide to form a precipitate; the reacted solution is left to stand for 45 minutes to make the precipitate settle; then, the precipitate is separated by a plate and frame filter press.

[0072] The pressure filtration residue is treated by acid leaching to recover the nickel and cobalt therein. The acid-ore ratio is 600kg / t, the stirring is carried out for 2 hours, the liquid-solid ratio is 6:1, the test temperature is 90℃, the stirring speed is 500r / min, and the nickel and cobalt recovery rate is 99%.

[0073] The treated solution is evaporated and crystallized at 60℃ to obtain magnesium sulfate crystals, which are then dried at 80℃ to constant weight to obtain the high-purity magnesium sulfate product.

[0074] The nickel content in the product is 0.1mg / L, the cobalt content is 0.1mg / L, and the magnesium loss rate is less than 0.15%. The quality requirements of high-purity magnesium sulfate are met.

[0075] Example 2

[0076] The difference from Example 1 is that when the sodium hydrosulfide solution is added to the pretreated solution, the amount of sodium hydrosulfide added is 1.5 times the theoretical equivalent of the total content of nickel and cobalt, and the pH value of the solution is controlled at 6.5. The other conditions are the same as those in Example 1.

[0077] The nickel content in the prepared high-purity magnesium sulfate product is 0.15mg / L, the cobalt content is 0.2mg / L, and the magnesium loss rate is less than 0.16%. The quality requirements of high-purity magnesium sulfate are met.

[0078] Example 3

[0079] The difference from Example 1 is that after the sodium hydrosulfide solution is added to the pretreated solution, the reaction temperature is 50℃. The other conditions are the same as those in Example 1.

[0080] The nickel content in the prepared high-purity magnesium sulfate product is 0.12mg / L, the cobalt content is 0.19mg / L, and the magnesium loss rate is less than 0.19%. The quality requirements of high-purity magnesium sulfate are met.

[0081] Example 4

[0082] The difference from Example 1 is that the polyethylene glycol 0.05g / L is added to the pretreated solution at the same time as the sodium hydrosulfide solution. The other conditions are the same as those in Example 1.

[0083] The prepared high-purity magnesium sulfate product has a nickel content of 0.10 mg / L, a cobalt content of 0.14 mg / L, and a magnesium loss rate of less than 0.15%, meeting the quality requirements of high-purity magnesium sulfate.

[0084] Example 5

[0085] The difference from Example 1 is that when the coconut shell activated carbon filter is treated with NaOH, the wt.% ratio of activated carbon / NaOH solution is 1:5, and the soaking time is 24 h; when the NaOH-treated coconut shell activated carbon filter is used for filtration, the flow rate is controlled at 1 m / h. The other conditions are the same as in Example 1.

[0086] The prepared high-purity magnesium sulfate product has a nickel content of 0.15 mg / L, a cobalt content of 0.18 mg / L, and a magnesium loss rate of less than 0.16%, meeting the quality requirements of high-purity magnesium sulfate.

[0087] Example 6

[0088] The difference from Example 1 is that the coconut shell activated carbon filter is not treated with NaOH. The other conditions are the same as in Example 1.

[0089] The prepared high-purity magnesium sulfate product has a nickel content of 0.19 mg / L, a cobalt content of 0.21 mg / L, and a magnesium loss rate of less than 0.18%, meeting the quality requirements of high-purity magnesium sulfate.

[0090] Comparative Example 1 (traditional alkali precipitation method)

[0091] Sodium hydroxide is used as a precipitant to adjust the pH value of the solution to 9.0, so that the nickel and cobalt ions form hydroxide precipitates. After treatment, the nickel content in the solution is 5 mg / L, and the cobalt content is 4 mg / L, which is much higher than the purification effect of the embodiments of the present application, and a large amount of waste residue is generated, resulting in high treatment cost.

[0092] This comparative example consumes a large amount of sodium hydroxide, and the amount of sodium hydroxide used is 7.6 times the theoretical equivalent of the total content of nickel and cobalt, increasing the production cost; at the same time, magnesium is co-precipitated, and the magnesium loss rate is >20%.

[0093] The unit price of industrial-grade sodium hydroxide is about 800 yuan / ton, and the reagent cost per ton of solution is 0.084 yuan, which is 61.54% higher than that of sodium hydrosulfide (1.5 times the theoretical amount, reagent cost per ton of solution is 0.052 yuan) in the present application.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that the reaction temperature is 70℃ after adding sodium hydrosulfide solution to the pretreated solution. The other conditions are the same as in Example 1.

[0096] The prepared high-purity magnesium sulfate product has nickel content of 0.16 mg / L, cobalt content of 0.17 mg / L, and magnesium loss rate of less than 0.89%.

[0097] The description of the application is given for the purpose of exemplification and description and is not intended to be exhaustive or to limit the application to the precise form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Embodiments were chosen and described in order to best explain the principles of the application and its practical application and to thereby enable others skilled in the art to best utilize the application with various modifications as are suited to the particular use contemplated.

Claims

1. A method for purifying magnesium sulfate solution, characterized in that, include: Pre-treat magnesium sulfate solution containing nickel and cobalt impurities to remove suspended solids and organic matter; adding sodium hydrosulfide to the pretreated magnesium sulfate solution, controlling the pH value of the solution between 6.5 and 7.5, stirring to allow nickel and cobalt to react with the sodium hydrosulfide to form precipitates, and performing solid-liquid separation to obtain a purified magnesium sulfate solution and a precipitate containing nickel sulfide and cobalt sulfide; The purified magnesium sulfate solution is evaporated and crystallized to obtain magnesium sulfate crystals, which are then dried to obtain a magnesium sulfate product; The precipitate containing nickel sulfide and cobalt sulfide is post-treated to recover nickel and cobalt.

2. The method for purifying magnesium sulfate solution according to claim 1, wherein In the step of pretreating the magnesium sulfate solution containing nickel and cobalt impurities, the magnesium sulfate solution is filtered through a quartz sand filter and an activated carbon filter in sequence.

3. The method for purifying magnesium sulfate solution according to claim 2, wherein In the quartz sand filter, the filter material particle size is 0.5 to 4 mm and the porosity is 40% to 45%; In the activated carbon filter, the filter material type is coconut shell activated carbon, the particle size range is 1.0-2.0 mm, and the filling height is 1000-1500 mm; When the magnesium sulfate solution is filtered using an activated carbon filter, the flow rate is controlled at 1 to 2 m / h.

4. The method for purifying magnesium sulfate solution according to claim 3, wherein In the activated carbon filter, the coconut shell activated carbon is activated carbon treated with alkalinity.

5. The method for purifying magnesium sulfate solution according to claim 1, wherein The amount of sodium hydrosulfide added is a theoretical equivalent of 1.5 to 2.5 times the total content of nickel and cobalt in the magnesium sulfate solution.

6. The method for purifying magnesium sulfate solution according to claim 1, wherein In the step of stirring nickel and cobalt to react with sodium hydrosulfide to form precipitates, the reaction temperature is 20-50° C., the stirring speed is 100-300 r / min, and the reaction time is 0.5-2 hours.

7. The method for purifying magnesium sulfate solution according to claim 1, wherein The magnesium sulfate product is a high-purity magnesium sulfate product.

8. The method for purifying magnesium sulfate solution according to claim 1, wherein The temperature of evaporation crystallization is controlled at 50-70°C; the temperature of drying treatment is controlled at 60-100°C.

9. The method for purifying magnesium sulfate solution according to claim 1, wherein Before the step of evaporating and crystallizing the purified magnesium sulfate solution, the method further includes: testing the purified magnesium sulfate solution to ensure that the nickel and cobalt contents are both less than 1.0 mg / L; The precipitate containing nickel sulfide and cobalt sulfide is treated by acid leaching to recover the nickel and cobalt therein; wherein, the acid-ore ratio is 500-900 kg / t, stirring is 1-3 hours, the liquid-solid ratio is 4-8:1, the temperature is 80-95°C, and the stirring speed is 300-800 r / min.

10. The method for purifying magnesium sulfate solution according to claim 1, wherein When sodium hydrosulfide is added to the pretreated magnesium sulfate solution, an auxiliary reagent is added, wherein the auxiliary reagent is one or more selected from a surfactant and a complexing agent.

11. A system for purifying magnesium sulfate solution for the method for purifying magnesium sulfate solution according to any one of claims 1 to 10, characterized in that: The system comprises: A pretreatment unit is used to pretreat the magnesium sulfate solution containing nickel and cobalt impurities to remove suspended solids and organic matter therein; The sodium hydrosulfide purification unit is used to add sodium hydrosulfide to the pretreated magnesium sulfate solution, control the pH value of the solution between 6.5 and 7.5, and stir to allow nickel and cobalt to react with the sodium hydrosulfide to form precipitates; A precipitation separation unit is used to perform solid-liquid separation on the material obtained from the sodium hydrosulfide purification unit to obtain a purified magnesium sulfate solution and a precipitate containing nickel sulfide and cobalt sulfide; The crystallization and drying unit is used to evaporate and crystallize the purified magnesium sulfate solution to obtain magnesium sulfate crystals, and then dry them to obtain magnesium sulfate products; The post-processing unit is used to post-process the precipitate containing nickel sulfide and cobalt sulfide to recover the nickel and cobalt therein.