CN112299451A - Method for preparing lithium hydroxide from lithium-containing low-magnesium brine in lithium phosphate form - Google Patents
Method for preparing lithium hydroxide from lithium-containing low-magnesium brine in lithium phosphate form Download PDFInfo
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Abstract
The invention provides a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, and relates to the technical field of lithium extraction in salt lakes. The method adopts inorganic alkaline compounds to adjust the pH value of the lithium-containing low-magnesium brine to more than 10 to precipitate calcium and magnesium, so as to obtain the lithium-containing brine without calcium and magnesium; adding a phosphoric acid solution for precipitation reaction, centrifuging and washing the obtained lithium phosphate precipitate, and dissolving the lithium phosphate precipitate in the phosphoric acid solution to obtain a lithium dihydrogen phosphate solution; and purifying the lithium dihydrogen phosphate solution, performing bipolar membrane electrodialysis, and concentrating and crystallizing the obtained lithium hydroxide solution to obtain a lithium hydroxide product. The method has simple and convenient operation, high removal rate of calcium, magnesium, sodium and potassium in the lithium-containing low-magnesium brine, high purity of the lithium hydroxide product after electrolysis, high material recycling rate and low cost, can continuously prepare the lithium hydroxide, and is particularly suitable for salt lake lithium extraction of Tibet, Qinghai and south America with remote geographical positions, high raw material transportation cost and low photovoltaic power generation and energy storage cost.
Description
Technical Field
The invention relates to the technical field of lithium extraction in salt lakes, in particular to a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate.
Background
At present, lithium element is widely used in various fields such as lithium batteries, glass, ceramics, alloys, lubricants, and medicines. Lithium resources can be classified into brine type and ore type according to their source. The process of extracting lithium from the ore comprises the steps of mineral separation, high-temperature calcination, leaching, purification, concentration, precipitation and the like of the ore such as spodumene, lepidolite, petalite, hectorite and the like, the processes need high energy consumption, the comprehensive cost of extracting lithium from the ore is high, and the price of lithium salt for extracting lithium from the ore is difficult to further reduce. Different from ore resources, the brine lithium resources contain dissolved lithium ions, compared with the process of extracting lithium from ore, the process of high-temperature calcination and leaching is omitted in the process of extracting lithium from salt lake brine, and the salt lake lithium extraction has the advantage of low cost naturally.
With the increase of the continuous mileage of the electric vehicle, a high nickel lithium battery represented by a tesla pine battery becomes an industry development trend, and battery-grade lithium hydroxide is needed for producing a positive electrode material of the high nickel lithium battery, so that the increase rate of the demand of the lithium hydroxide is obviously faster than that of lithium carbonate in the future.
At present, lithium hydroxide is produced by extracting lithium from salt lakes, lithium chloride is generally used for producing lithium carbonate, and then lithium hydroxide is produced by taking the lithium carbonate as a raw material and adopting a causticizing method. The patent CN106011917A abandons the traditional method, lithium chloride solution with the lithium ion content of 8-30 g/L, the sodium ion content of 6-20 g/L, the potassium ion content of less than or equal to 1500ppm, the total content of calcium and magnesium ions of less than or equal to 0.15ppm and the total content of sulfate radical and boron elements of less than or equal to 50ppm is used for ion membrane electrolytic cell electrolysis, and light salt water and chlorine are obtained at the anode side; and obtaining a mixed solution of hydrogen, lithium hydroxide, sodium hydroxide and trace potassium hydroxide on the cathode side. However, the concentration of sodium ions and potassium ions in the lithium chloride solution before electrolysis is high, and sodium hydroxide and potassium hydroxide are generated in the electrolysis process, so that firstly, the electrolysis production energy is reduced, the electrolysis cost is increased, and secondly, the cost and difficulty of producing a battery-grade lithium hydroxide product from a mixed solution of lithium hydroxide, sodium hydroxide and trace potassium hydroxide are increased.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate. The method provided by the invention is simple and convenient to operate, and has high removal rate of calcium, magnesium, sodium and potassium in the lithium-containing low-magnesium brine, so that the purity of the lithium hydroxide product is improved.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, which comprises the following steps:
(1) adjusting the pH value of the lithium-containing low-magnesium brine to more than 10 by adopting an inorganic alkaline compound to precipitate calcium and magnesium, so as to obtain the lithium-containing brine without calcium and magnesium; the concentration of lithium in the lithium-containing low-magnesium brine is more than 0.5g/L, and the concentration of magnesium is less than 6 g/L;
(2) adding a phosphoric acid solution into the lithium-containing brine from which calcium and magnesium are removed for precipitation reaction to obtain lithium phosphate precipitate;
(3) sequentially centrifuging and washing the lithium phosphate precipitate, and dissolving the lithium phosphate precipitate in a phosphoric acid solution to obtain a lithium dihydrogen phosphate solution;
(4) purifying the lithium dihydrogen phosphate solution, and performing bipolar membrane electrodialysis to obtain a lithium hydroxide solution and a phosphoric acid solution;
(5) and sequentially concentrating and crystallizing the lithium hydroxide solution to obtain lithium hydroxide and lithium hydroxide precipitation mother liquor.
Preferably, the lithium-containing low-magnesium brine comprises one or more of lithium-containing low-magnesium salt lake brine, lithium-containing low-magnesium desorption liquid prepared by removing impurities and concentrating lithium from salt lake brine through an adsorption method, lithium-containing low-magnesium concentrated liquid obtained by reverse osmosis of the lithium-containing low-magnesium desorption liquid, lithium-containing low-magnesium electrodialysis concentrated liquid obtained by monovalent ion selective electrodialysis treatment of the salt lake brine, lithium-containing low-magnesium nanofiltration solution obtained by nanofiltration magnesium removal treatment of the salt lake brine, lithium-containing low-magnesium brine obtained by adding sodium carbonate or sodium bicarbonate into high-magnesium brine to remove magnesium, underground brine, lithium precipitation mother liquor, lithium battery waste leachate and lithium ore leachate.
Preferably, the inorganic alkaline compound in step (1) comprises one or more of lithium hydroxide, sodium carbonate, calcium hydroxide, potassium hydroxide and ammonia water.
Preferably, the reaction temperature of the precipitation reaction in the step (2) is 40-95 ℃.
Preferably, the purification in the step (4) comprises performing plate-frame filtration, multi-media filtration, ultrafiltration and resin adsorption on the lithium dihydrogen phosphate solution in sequence; the concentration of lithium in the purified lithium dihydrogen phosphate solution is 2-25 g/L.
Preferably, the bipolar membrane electrodialysis in the step (4) is carried out in a bipolar membrane electrodialysis device;
the bipolar membrane electrodialysis device comprises an anode chamber, a bipolar membrane, a membrane stack and a cathode chamber which are sequentially arranged, wherein the membrane stack is composed of an anion selective dialysis membrane, a cation selective dialysis membrane and the bipolar membrane which are repetitive units; the anion selective side of the bipolar membrane faces the cation selective dialysis membrane.
Preferably, the bipolar membrane electrodialysis comprises the steps of:
introducing the purified lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane, introducing a low-concentration phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane, introducing a low-concentration lithium hydroxide solution between the bipolar membrane and the cation selective dialysis membrane, and respectively adding a lithium hydroxide solution into the cathode chamber and the anode chamber to serve as electrode solutions; then electrifying the bipolar membrane electrodialysis device to carry out bipolar membrane electrodialysis; the mass concentration of phosphoric acid in the low-concentration phosphoric acid solution is 2-22%, and the concentration of lithium in the low-concentration lithium hydroxide solution is 0.1-20 g/L.
Preferably, the voltage applied to each membrane stack unit in the bipolar membrane electrodialysis process is 1.2-3.0V, and the current density is 180-600A/m2。
Preferably, the bipolar membrane electrodialysis further comprises, after the bipolar membrane electrodialysis: and (3) recycling the phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane for preparing the lithium phosphate precipitate in the step (2) or recycling the phosphoric acid solution for preparing the lithium dihydrogen phosphate solution in the step (3).
Preferably, the bipolar membrane electrodialysis further comprises, after the bipolar membrane electrodialysis: and concentrating and purifying the lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane, and then recycling the lithium dihydrogen phosphate solution for bipolar membrane electrodialysis.
Preferably, the lithium hydroxide precipitation mother liquor is recycled for the step (1) of adjusting the pH value of the lithium-containing low-magnesium brine.
The invention provides a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, which comprises the following steps: (1) adjusting the pH value of the lithium-containing low-magnesium brine to more than 10 by adopting an inorganic alkaline compound to precipitate calcium and magnesium, so as to obtain the lithium-containing brine without calcium and magnesium; the concentration of lithium in the lithium-containing low-magnesium brine is more than 0.5g/L, and the concentration of magnesium is less than 6 g/L; (2) adding a phosphoric acid solution into the lithium-containing brine from which calcium and magnesium are removed for precipitation reaction to obtain lithium phosphate precipitate; (3) sequentially centrifuging and washing the lithium phosphate precipitate, and dissolving the lithium phosphate precipitate in a phosphoric acid solution to obtain a lithium dihydrogen phosphate solution; (4) purifying the lithium dihydrogen phosphate solution, and performing bipolar membrane electrodialysis to obtain a lithium hydroxide solution and a phosphoric acid solution; (5) and sequentially concentrating and crystallizing the lithium hydroxide solution to obtain lithium hydroxide and lithium hydroxide precipitation mother liquor. Firstly, adding alkali into lithium-containing low-magnesium brine to remove calcium and magnesium in the brine, then adding a phosphoric acid solution to generate a lithium phosphate precipitate, enriching lithium and simultaneously realizing the separation of lithium, sodium and potassium, then dissolving the lithium phosphate precipitate into the phosphoric acid solution, and then performing bipolar membrane electrodialysis on the obtained lithium dihydrogen phosphate solution. The method provided by the invention is simple and convenient to operate, and has high removal rate of calcium, magnesium, sodium and potassium in the lithium-containing low-magnesium brine, so that the purity of the electrolyzed lithium hydroxide product is improved.
Further, the phosphoric acid solution obtained after the bipolar membrane electrodialysis is reused for preparing lithium phosphate precipitate or preparing lithium dihydrogen phosphate solution, the lithium dihydrogen phosphate solution after the bipolar membrane electrodialysis is concentrated and purified and then reused for the bipolar membrane electrodialysis, and lithium hydroxide precipitation lithium mother liquor after the lithium hydroxide solution is concentrated and crystallized is reused for adjusting the pH value of the lithium-containing low-magnesium brine. The method provided by the invention has the advantages of high material recycling rate and low cost, can continuously prepare the lithium hydroxide, and is particularly suitable for lithium extraction in salt lakes of Tibet, Qinghai and south America, which have the advantages of remote geographical positions, high raw material transportation cost and low photovoltaic power generation and energy storage cost.
Drawings
FIG. 1 is a schematic diagram of the bipolar membrane electrodialysis device and the principle thereof, in FIG. 1, a 1-bipolar membrane, a 2-anion selective dialysis membrane, a 3-cation selective dialysis membrane, a 4-anode and a 5-cathode are shown.
Detailed Description
The invention provides a method for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, which comprises the following steps:
(1) adjusting the pH value of the lithium-containing low-magnesium brine to more than 10 by adopting an inorganic alkaline compound to precipitate calcium and magnesium, so as to obtain the lithium-containing brine without calcium and magnesium; the concentration of lithium in the lithium-containing low-magnesium brine is more than 0.5g/L, and the concentration of magnesium is less than 6 g/L;
(2) adding a phosphoric acid solution into the lithium-containing brine from which calcium and magnesium are removed for precipitation reaction to obtain lithium phosphate precipitate;
(3) sequentially centrifuging and washing the lithium phosphate precipitate, and dissolving the lithium phosphate precipitate in a phosphoric acid solution to obtain a lithium dihydrogen phosphate solution;
(4) purifying the lithium dihydrogen phosphate solution, and performing bipolar membrane electrodialysis to obtain a lithium hydroxide solution and a phosphoric acid solution;
(5) and sequentially concentrating and crystallizing the lithium hydroxide solution to obtain lithium hydroxide and lithium hydroxide precipitation mother liquor.
The invention adopts inorganic alkaline compound to adjust the pH value of the lithium-containing low-magnesium brine to more than 10 to precipitate calcium and magnesium, and the lithium-containing brine without calcium and magnesium is obtained; the concentration of lithium in the lithium-containing low-magnesium brine is more than 0.5g/L, and the concentration of magnesium is less than 6 g/L. In the invention, the lithium-containing low-magnesium brine preferably comprises one or more of lithium-containing low-magnesium salt lake brine, lithium-containing low-magnesium desorption liquid prepared by removing impurities and concentrating lithium from salt lake brine through an adsorption method, lithium-containing low-magnesium concentrated liquid obtained by reverse osmosis of the lithium-containing low-magnesium desorption liquid, lithium-containing low-magnesium electrodialysis concentrated liquid obtained by monovalent ion selective electrodialysis treatment of the salt lake brine, lithium-containing low-magnesium nanofiltration solution obtained by removing magnesium from the salt lake brine through nanofiltration, lithium-containing low-magnesium brine obtained by adding sodium carbonate or sodium bicarbonate into high-magnesium brine and removing magnesium, underground brine, lithium-precipitating mother liquor, lithium battery waste leachate and lithium ore leachate. The invention has no special requirements on various methods for obtaining the lithium-containing low-magnesium brine, and the corresponding methods well known by the technical personnel in the field can be adopted.
In the present invention, the inorganic basic compound preferably includes one or more of lithium hydroxide, sodium carbonate, calcium hydroxide, potassium hydroxide, and ammonia water. The inorganic alkaline compound is preferably adopted to adjust the pH value of the lithium-containing low-magnesium brine to 11-12.5.
The carbonate type salt lake brine such as Tibet Zaubu, Jie Ruan and Dang Xiong is taken as an example for explanation, and the carbonate type salt lake brine comprises the conventional components of Li+、Na+、K+、Ca2+、Mg2+、Cl-、CO3 2-、HCO3 -、SO4 2-Plasma, adding alkali into the lithium-containing brine to increase the pH value of the solution to more than 10 and remove Ca2+、Mg2+High valence cation impurity to make Ca in brine2+And Mg2+With Ca (OH)2、CaCO3Basic magnesium carbonate, Mg (OH)2To remove calcium and magnesium from the lithium-containing low-magnesium brine.
After the lithium-containing brine without calcium and magnesium is obtained, the lithium-containing brine without calcium and magnesium is added with a phosphoric acid solution for precipitation reaction to obtain lithium phosphate precipitate. In the present invention, the phosphoric acid solution preferably has a mass concentration of 8.7%; the molar weight of phosphoric acid in the phosphoric acid solution is preferably 33-45% of the molar weight of lithium. In the invention, the reaction temperature of the precipitation reaction is preferably 40-95 ℃, and more preferably 50-80 ℃. In the invention, the precipitation reaction is preferably carried out under the condition of stirring, and the stirring time is preferably 20-30 min. Adding a phosphoric acid solution into the lithium-containing brine from which calcium and magnesium are removed, wherein the phosphoric acid solution reacts with residual alkali in the brine on one hand and reacts with lithium ions in the brine on the other hand to produce precipitates, and the separation of lithium, sodium, potassium and boron is realized while enriching lithium; the course of the precipitation reaction is shown in equation 1. The solubility of lithium phosphate is about 0.39g/L, corresponding to a lithium ion concentration of 0.07g/L, which is much lower than that of lithium carbonate. After the precipitation reaction, the lithium phosphate precipitate is preferably separated from the brine by filtration, which is not particularly required by the present invention, and which is well known to those skilled in the art.
Reaction formula 1: h3PO4+3OH-+3Li+→3H2O+Li3PO4↓
After the lithium phosphate precipitate is obtained, the lithium phosphate precipitate is sequentially centrifuged and washed, and then dissolved in a phosphoric acid solution to obtain a lithium dihydrogen phosphate solution. The method of centrifugation is not particularly required in the present invention, and a centrifugation method well known to those skilled in the art may be used; the method removes impurities such as water, sodium, potassium and the like which are remained in lithium phosphate precipitation through centrifugation. In the invention, the washing is preferably deionized water washing, and Na remained on lithium phosphate is further removed by water washing+、K+、Cl-、SO4 2-Boron, and the like. In the present invention, the phosphoric acid in the phosphoric acid solution is twice as much as the lithium phosphate precipitate. After adding the phosphoric acid solution, the phosphoric acid solution and lithium phosphate mainly generate lithium dihydrogen phosphate (LiH)2PO4) The solubility of lithium dihydrogen phosphate is 1260g/L (0 ℃), and the corresponding lithium ion concentration is 84.8 g/L; in addition, dilithium hydrogen phosphate (Li) may be formed in the solution2HPO4) The solubility of dilithium hydrogenphosphate was 44.3g/L (0 ℃ C.), corresponding to a lithium ion concentration of 5.6 g/L; the main reaction of phosphoric acid solution and lithium phosphate precipitation occurs as shown in equation 2:
reaction formula 2: 2H3PO4+Li3PO4→3Li++3H2PO4 -
After the lithium dihydrogen phosphate solution is obtained, the lithium dihydrogen phosphate solution is purified and subjected to bipolar membrane electrodialysis to obtain a lithium hydroxide solution and a phosphoric acid solution. In the invention, the purification comprises plate-frame filtration, multi-medium filtration, ultrafiltration and resin adsorption of the lithium dihydrogen phosphate solution in sequence. In the present invention, the plate and frame filtration is carried out in a plate and frame filter press; the plate-frame filter press is an intermittent solid-liquid separation device, and is characterized in that filter plates and filter frames are arranged to form filter chambers, feed liquid is fed into each filter chamber under the pressure action of a feed delivery pump, and solid and liquid are separated through a filter medium. The invention has no special requirements on the plate and frame filter press, and can adopt corresponding devices which are well known to the technical personnel in the field, and the invention has no special requirements on the operation method of the plate and frame filter, and can adopt the operation method which is well known to the technical personnel in the field. In the invention, the pressure of the plate-and-frame filtration is preferably 0.3-3 MPa, and the filtration pore size is preferably 3-10 microns. In the invention, the multi-medium filtration is carried out in a multi-medium filter which is of a columnar, rectangular or square structure and comprises a plurality of layers of filter media, wherein the upper layer of the filter media is a relatively fine filter material such as activated carbon, and the lower layer of the filter media is a relatively high-density filter material, and the multi-medium filter realizes more excellent filtering effect by utilizing the plurality of media and is mainly used for removing suspended matters, colloids, organic matters and the like in raw water; if necessary, the multimedia filter may be pressurized to facilitate filtration. In the invention, the ultrafiltration uses the pressure difference at two sides of the ultrafiltration membrane as a driving force, the ultrafiltration membrane is used as a filtering medium, under a certain pressure, when a stock solution flows across the surface of the membrane, a plurality of fine micropores densely distributed on the surface of the ultrafiltration membrane only allow water and small molecular substances to pass through to form a permeate, and substances with a volume larger than the micropore diameter of the surface of the membrane in the stock solution are intercepted, so that the purposes of purifying, separating and concentrating the stock solution are realized, and the contents of COD (chemical oxygen demand), SS (suspended substances) and macromolecular dissolved substances in water can be greatly reduced through ultrafiltration. In the invention, the aperture of the ultrafiltration membrane is preferably 0.01-0.05 micron. In the invention, the resin used for resin adsorption is preferably ion exchange resin and/or chelating resin; the invention selectively separates specific metal ions from a solution containing the metal ions through the resin in the form of ionic bonds or coordinate bonds, and particularly removes divalent and above metal ions.
In the invention, the concentration of lithium in the purified lithium dihydrogen phosphate solution is preferably 2-25 g/L, and more preferably 8-16 g/L.
Through the purification process, the quality of the lithium dihydrogen phosphate solution meets the water inlet quality requirement of bipolar membrane electrodialysis, and a battery-grade lithium hydroxide product is easily prepared. In the invention, the water inlet quality requirement of the bipolar membrane electrodialysis is as follows: the water temperature is 20-35 ℃; COD (chemical oxygen demand) < 20mg/L, wherein the organic matter component cannot contain aromatic hydrocarbons; turbidity < 1 NTU; the oil content is less than 0.1 mg/L; the surfactant is less than 0.1 mg/L; SS (suspended substance) < 1 mg/L; the silicon dioxide is less than 1 mg/L; iron is less than 0.3 mg/L; manganese is less than 0.1 mg/L; mg (magnesium)2+，Ca2+Less than 1 mg/L; other high valence heavy metal ions are less than 0.1 mg/L.
After purification, the bipolar membrane electrodialysis is carried out on the purified lithium dihydrogen phosphate solution to obtain a lithium hydroxide solution and a phosphoric acid solution. In the present invention, the bipolar membrane electrodialysis is carried out in a bipolar membrane electrodialysis device; the bipolar membrane electrodialysis device preferably comprises an anode chamber, a bipolar membrane, a membrane stack and a cathode chamber which are sequentially arranged, wherein the membrane stack is composed of an anion selective dialysis membrane, a cation selective dialysis membrane and the bipolar membrane which are repetitive units; the bipolar membrane is a membrane formed by compounding an anion selective dialysis membrane and a cation selective dialysis membrane, one side of the bipolar membrane has cation selective permeability, the other side of the bipolar membrane has anion selective permeability, and the anion selective side of the bipolar membrane faces to the cation selective dialysis membrane. In the invention, the bipolar membrane electrodialysis takes potential difference as driving force, and utilizes the selective permeability of an anion-cation exchange membrane and the bipolar membrane to decompose water to generate H+And OH-To prepare the acid and base. In the present invention, the bipolar membrane electrodialysis device and the schematic diagram are shown in FIG. 1, a 1-bipolar membrane, a 2-anion selective dialysis membrane, a 3-cation selective dialysis membrane, a 4-anode, and a 5-cathode are shown.
In the present invention, the bipolar membrane electrodialysis preferably comprises the steps of: introducing the purified lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane, introducing a low-concentration phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane, introducing a low-concentration lithium hydroxide solution between the bipolar membrane and the cation selective dialysis membrane, and respectively adding a lithium hydroxide solution into the cathode chamber and the anode chamber to serve as electrode solutions; and then electrifying the bipolar membrane electrodialysis device to carry out bipolar membrane electrodialysis. In the invention, the mass concentration of phosphoric acid in the low-concentration phosphoric acid solution is preferably 2-22%, and more preferably 2-6%; the concentration of lithium in the low-concentration lithium hydroxide solution is preferably 0.1-20 g/L, and more preferably 0.5-5 g/L.
In the invention, the voltage applied to each membrane stack unit in the bipolar membrane electrodialysis process is preferably 1.2-3.0V, and the current density is preferably 180-600A/m2. Lithium ions (Li) in a lithium dihydrogen phosphate solution during bipolar membrane electrodialysis+) Passing through cation selective dialysis membrane to reach between anion selective side of bipolar membrane and cation selective dialysis membrane, and obtaining anion (H) in lithium dihydrogen phosphate solution2PO4 -) Passing through the anion selective dialysis membrane to a location between the cation selective side of the bipolar membrane and the anion selective dialysis membrane; water electrolysis in bipolar membranes to generate hydrogen ions (H)+) And hydroxide ion (OH)-) Hydrogen ions pass through the cation selective side of the bipolar membrane to reach between the cation selective side of the bipolar membrane and the anion selective dialysis membrane, and H2PO4 -Combining to generate phosphoric acid, and allowing hydroxide ions to pass through the anion selective side of the bipolar membrane to reach between the anion selective side of the bipolar membrane and the cation selective dialysis membrane to combine with lithium ions to generate lithium hydroxide. Further, oxygen is generated on the anode surface in the anode chamber, and hydrogen is generated on the cathode surface in the cathode chamber. As the electrodialysis proceeds, the concentration of the lithium dihydrogen phosphate solution added between the cation-selective dialysis membrane and the anion-selective dialysis membrane decreases, the concentration of the low-concentration phosphoric acid solution added between the bipolar membrane and the anion-selective dialysis membrane increases, and the concentration of the low-concentration lithium hydroxide solution added between the bipolar membrane and the cation-selective dialysis membrane increases. As a result, a lithium dihydrogen phosphate solution is obtained in high concentration by a bipolar membrane electrodialysis processLithium hydroxide solution and phosphoric acid solution, while obtaining a low concentration lithium dihydrogen phosphate solution as a by-product.
After electrodialysis is carried out, the mass concentration of phosphoric acid in a phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane is preferably 2-25%, and more preferably 5-12%; the concentration of lithium in the lithium hydroxide solution between the bipolar membrane and the cation selective dialysis membrane is preferably 0.1-30 g/L, and preferably 6-20 g/L; the concentration of lithium in the lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane is preferably 2-20 g/L, and more preferably 2-12 g/L.
After electrodialysis is carried out, the phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane is preferably recycled for the process for preparing lithium phosphate precipitate in the scheme, or for the process for preparing lithium dihydrogen phosphate solution in the scheme; the lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane is preferably concentrated and purified and then is recycled for the electrodialysis process.
After the lithium hydroxide solution is obtained through the bipolar membrane electrodialysis process, the lithium hydroxide solution is sequentially concentrated and crystallized to obtain lithium hydroxide and lithium hydroxide precipitation mother liquor. In the present invention, the concentration and crystallization include one or more of reverse osmosis concentration, electrodialysis concentration, MVR evaporative concentration, single-effect evaporative concentration crystallization, and multi-effect evaporative concentration crystallization. The invention has no special requirements on the reverse osmosis concentration, the electrodialysis concentration, the MVR evaporation concentration, the single-effect evaporation concentration crystallization and the multi-effect evaporation concentration crystallization, and adopts corresponding devices and operations which are well known by the technical personnel in the field. After lithium hydroxide and lithium hydroxide precipitation mother liquor are obtained, the lithium hydroxide precipitation mother liquor is preferably recycled for adjusting the pH value of the lithium-containing low-magnesium brine in the scheme.
The following examples are provided to illustrate the preparation of lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, but they should not be construed as limiting the scope of the invention.
Example 1
The composition of Tibet Zaubuye salt lake brine is shown in Table 1, the salt lake brine has pH of 9.2 and density of 1.24g/cm3。
TABLE 1 Zabu Ye salt lake brine composition
| Composition (I) | K+ | Ca2+ | Mg2+ | Cl- | CO3 2- | SO4 2- | B2O3 | Li+ | Na+ |
| Concentration (g/L) | 31.6 | 0.002 | 0.02 | 120.6 | 34.1 | 29.8 | 8.4 | 0.81 | 100.1 |
Taking 100L of the salt lake brine sample, adding lithium hydroxide lithium precipitation mother liquor to adjust the pH value to 11, filtering to remove generated precipitates to obtain a brine sample after calcium and magnesium removal, analyzing the lithium concentration in the brine sample to be 0.79g/L by using plasma inductively coupled atomic emission spectroscopy (ICP), and analyzing the calcium and magnesium content in the brine sample, wherein Mg and Ca in the solution are both smaller than the ICP-AES inspection limit, so that the calcium and magnesium are completely removed;
taking 50L of a halogen water sample after calcium and magnesium removal, wherein the total lithium content is 39.5g, adding 2500g of phosphoric acid with the mass fraction of 8.7%, and stirring and reacting for 30 minutes at 50 ℃; after completion, the reaction mass was filtered to separate lithium phosphate precipitated therein, and centrifuged, washed and dried to obtain 165g of lithium phosphate product, which was determined to have a purity of 99% by ICP analysis, indicating that about 75% of the lithium therein was converted to lithium phosphate precipitate;
dissolving 100g of the lithium phosphate with the purity of 99 percent in a phosphoric acid solution with the mass fraction of 8.7 percent in twice equivalent, and sequentially carrying out plate-frame filtration, multi-medium filtration, ultrafiltration and chelate resin adsorption treatment to prepare LiH with the lithium concentration of 10g/L2PO41.8L of solution, wherein the concentration of sodium ions is 0.3g/L, the concentration of potassium ions is 0.1g/L, and other water quality is as follows: the water temperature is 20-35 ℃; COD (chemical oxygen demand) < 20mg/L, wherein the organic matter component does not contain aromatic hydrocarbons; turbidity < 1 NTU; the oil content is less than 0.1 mg/L; the surfactant is less than 0.1 mg/L; SS (suspended substance) < 1 mg/L; the silicon dioxide is less than 1 mg/L; iron is less than 0.3 mg/L; manganese is less than 0.1 mg/L; mg (magnesium)2+，Ca2+Less than 1 mg/L; other high-valence heavy metal ions are less than 0.1 mg/L;
adding 1L lithium dihydrogen phosphate solution with lithium concentration of 10g/L, 1L lithium hydroxide solution with lithium concentration of 1g/L and 1L phosphoric acid solution with mass fraction of 5% into bipolar membrane electrodialysis device as shown in FIG. 1, applying voltage of 1.8V and current density of each membrane stack unitIs 300A/m2(ii) a Through electrodialysis, the lithium concentration in lithium dihydrogen phosphate is reduced to 2g/L, and the lithium concentration in the lithium hydroxide aqueous solution is increased to 9g/L, so that the lithium primary conversion rate is 80%, a phosphoric acid solution with the mass fraction of 8.7% is generated, and the phosphoric acid solution is recycled;
and performing electrodialysis concentration and MVR evaporation concentration crystallization on the prepared lithium hydroxide solution to obtain a battery-grade lithium hydroxide product with the main content of 99.5% and lithium hydroxide precipitation lithium mother liquor, wherein the lithium hydroxide precipitation lithium mother liquor is reused for removing calcium and magnesium from brine.
Example 2
The underground brine in Jiangxi mainly comprises the following components in percentage by weight (g/L): li+，0.097；Mg2+，0.929；Na+，120.6；K+，0.421；Ca2+，4.045；Cl-196.7, preparing desorption solution containing lithium and low magnesium by removing magnesium and concentrating lithium by an adsorption method of an aluminum adsorbent, wherein the desorption solution mainly comprises the following components in percentage by weight (g/L): li+，0.23；Mg2+，0.004；Na+，0.43；K+，0.002；Ca2+，0.015；Cl-And 1.88, further performing reverse osmosis on the desorption solution to obtain a lithium-containing low-magnesium concentrated solution, wherein the concentrated solution mainly comprises the following components in percentage by mass (g/L): li+，2.3；Mg2+，0.04；Na+，4.3；K+，0.02；Ca2+，0.15；Cl-，18.8。
Taking 100L of the concentrated solution, adding lithium hydroxide lithium precipitation mother liquor and sodium hydroxide solution to adjust the pH value to 11.5, filtering to remove generated precipitate to obtain a calcium and magnesium removed halogen water sample, analyzing the lithium concentration in the halogen water sample to be 2.25g/L by using plasma inductively coupled atomic emission spectrometry (ICP), and simultaneously analyzing the calcium and magnesium content in the halogen water sample and the Mg content in the solution2+And Ca2+The calcium and the magnesium are completely removed when the calcium and the magnesium are both less than the checking limit of ICP-AES;
taking 50L of a halogen water sample after calcium and magnesium removal, wherein the total lithium content is 112.5g, adding 7200g of phosphoric acid with the mass fraction of 8.8%, and stirring and reacting for 20 minutes at 80 ℃; after completion, the reaction mass was filtered to separate lithium phosphate precipitated therein, and centrifuged, dehydrated, washed, and dried to obtain 535g of lithium phosphate product, which was determined to have a purity of 99.2% by ICP analysis, indicating that about 85% of the lithium therein was converted to lithium phosphate precipitate;
dissolving 100g of the lithium phosphate with the purity of 99.2 percent in a phosphoric acid solution with the mass fraction of 8.8 percent in twice equivalent, and preparing the LiH with the lithium concentration of 8g/L after plate-and-frame filtration, multi-medium filtration, ultrafiltration and chelate resin adsorption treatment in sequence2PO42.25L of solution, wherein the concentration of sodium ions is 0.1g/L, the concentration of potassium ions is 0.005g/L, and other water quality is as follows: the water temperature is 20-35 ℃; COD (chemical oxygen demand) < 20mg/L, wherein the organic matter component does not contain aromatic hydrocarbons; turbidity < 1 NTU; the oil content is less than 0.1 mg/L; the surfactant is less than 0.1 mg/L; SS (suspended substance) < 1 mg/L; the silicon dioxide is less than 1 mg/L; iron is less than 0.3 mg/L; manganese is less than 0.1 mg/L; mg (magnesium)2+，Ca2+Less than 1 mg/L; other high-valence heavy metal ions are less than 0.1 mg/L;
1L of a lithium dihydrogen phosphate aqueous solution having a lithium concentration of 8g/L, 1L of a lithium hydroxide solution having a lithium concentration of 0.5g/L and 1L of a phosphoric acid solution having a mass fraction of 6%, as shown in FIG. 1, were charged into a bipolar membrane electrodialysis device, and a voltage of 1.6V and a current density of 250A/m were applied to each membrane stack unit2(ii) a Through electrodialysis, the lithium concentration in lithium dihydrogen phosphate is reduced to 2g/L, and the lithium concentration in the lithium hydroxide aqueous solution is increased to 6.5g/L, so that the lithium primary conversion rate is 75%, a phosphoric acid solution with the mass fraction of 8.8% is generated, and the phosphoric acid solution is recycled;
and carrying out multi-effect evaporation, concentration and crystallization on the prepared lithium hydroxide solution to obtain a battery-grade lithium hydroxide product with the main content of 99.7% and lithium hydroxide precipitation mother liquor, and reusing the lithium hydroxide precipitation mother liquor for removing calcium and magnesium from brine.
The embodiment shows that the method provided by the invention is simple and convenient to operate, has high removal rate of calcium, magnesium, sodium and potassium in brine, improves the purity of the lithium hydroxide product, has high material recycling rate and low cost, and can continuously prepare the lithium hydroxide.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (11)
1. A process for preparing lithium hydroxide from lithium-containing low-magnesium brine in the form of lithium phosphate, comprising the steps of:
(1) adjusting the pH value of the lithium-containing low-magnesium brine to more than 10 by adopting an inorganic alkaline compound to precipitate calcium and magnesium, so as to obtain the lithium-containing brine without calcium and magnesium; the concentration of lithium in the lithium-containing low-magnesium brine is more than 0.5g/L, and the concentration of magnesium is less than 6 g/L;
(2) adding a phosphoric acid solution into the lithium-containing brine from which calcium and magnesium are removed for precipitation reaction to obtain lithium phosphate precipitate;
(3) sequentially centrifuging and washing the lithium phosphate precipitate, and dissolving the lithium phosphate precipitate in a phosphoric acid solution to obtain a lithium dihydrogen phosphate solution;
(4) purifying the lithium dihydrogen phosphate solution, and performing bipolar membrane electrodialysis to obtain a lithium hydroxide solution and a phosphoric acid solution;
(5) and sequentially concentrating and crystallizing the lithium hydroxide solution to obtain lithium hydroxide and lithium hydroxide precipitation mother liquor.
2. The method according to claim 1, wherein the lithium-containing low-magnesium brine comprises one or more of lithium-containing low-magnesium salt lake brine, lithium-containing low-magnesium desorption solution prepared by removing impurities and concentrating lithium from salt lake brine through an adsorption method, lithium-containing low-magnesium concentrated solution obtained by reverse osmosis of the lithium-containing low-magnesium desorption solution, lithium-containing low-magnesium electrodialysis concentrated solution obtained by monovalent ion selective electrodialysis treatment of salt lake brine, lithium-containing low-magnesium nanofiltration solution obtained by removing magnesium from salt lake brine through nanofiltration, lithium-containing low-magnesium brine obtained by adding sodium carbonate or sodium bicarbonate into high-magnesium brine and removing magnesium from the high-magnesium brine, underground brine, lithium precipitation mother liquor, lithium battery waste leachate and lithium ore leachate.
3. The method according to claim 1, wherein the inorganic alkaline compound in step (1) comprises one or more of lithium hydroxide, sodium carbonate, calcium hydroxide, potassium hydroxide and ammonia water.
4. The method according to claim 1, wherein the precipitation reaction in the step (2) is carried out at a reaction temperature of 40 to 95 ℃.
5. The method according to claim 1, wherein the purification in step (4) comprises subjecting the lithium dihydrogen phosphate solution to plate-and-frame filtration, multi-media filtration, ultrafiltration and resin adsorption in this order; the concentration of lithium in the purified lithium dihydrogen phosphate solution is 2-25 g/L.
6. The process according to claim 1 or 5, characterized in that the bipolar membrane electrodialysis in step (4) is carried out in a bipolar membrane electrodialysis device;
the bipolar membrane electrodialysis device comprises an anode chamber, a bipolar membrane, a membrane stack and a cathode chamber which are sequentially arranged, wherein the membrane stack is composed of an anion selective dialysis membrane, a cation selective dialysis membrane and the bipolar membrane which are repetitive units; the anion selective side of the bipolar membrane faces the cation selective dialysis membrane.
7. The method according to claim 6, characterized in that said bipolar membrane electrodialysis comprises the following steps:
introducing the purified lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane, introducing a low-concentration phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane, introducing a low-concentration lithium hydroxide solution between the bipolar membrane and the cation selective dialysis membrane, and respectively adding a lithium hydroxide solution into the cathode chamber and the anode chamber to serve as electrode solutions; then electrifying the bipolar membrane electrodialysis device to carry out bipolar membrane electrodialysis;
the mass concentration of phosphoric acid in the low-concentration phosphoric acid solution is 2-22%, and the concentration of lithium in the low-concentration lithium hydroxide solution is 0.1-20 g/L.
8. The method of claim 7, wherein the step of removing the metal oxide is performed by a chemical vapor deposition processIn the bipolar membrane electrodialysis process, the voltage applied to each membrane stack unit is 1.2-3.0V, and the current density is 180-600A/m2。
9. The method of claim 7, further comprising, after the bipolar membrane electrodialysis: and (3) recycling the phosphoric acid solution between the bipolar membrane and the anion selective dialysis membrane for preparing the lithium phosphate precipitate in the step (2) or recycling the phosphoric acid solution for preparing the lithium dihydrogen phosphate solution in the step (3).
10. The method of claim 7, further comprising, after the bipolar membrane electrodialysis: and concentrating and purifying the lithium dihydrogen phosphate solution between the cation selective dialysis membrane and the anion selective dialysis membrane, and then recycling the lithium dihydrogen phosphate solution for bipolar membrane electrodialysis.
11. The method of claim 1, wherein the lithium hydroxide precipitation mother liquor is recycled for adjusting the pH value of the lithium-containing low-magnesium brine in the step (1).
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