Patent Description:
Lithium is an important rare element, known as an "energy metal" and an "important element to promote the world forward. " Lithium metal and its compounds have been widely used in the fields of electronics, metallurgy, chemical industry, medicine, nuclear energy, aerospace and energy. Lithium resources exist in the form of solid mines and salt lake brines; since salt lakes are rich in lithium resources and the production cost is low, at present, the field of lithium extraction that is relatively mature and enables large-scale production is the extraction of lithium from salt lakes.

Researchers have done a lot of research on the extraction of lithium and developed a variety of technologies, including precipitation and calcination process, membrane separation technology, adsorption technology, ion exchange technology and solvent extraction technology. Among them, the solvent extraction technology has large processing capacity, simple operation and low pollution, thus being extensively researched and developed. The Patent <CIT> discloses a solvent extraction method for extracting lithium from a high-magnesium solution. In the method, lithium is extracted preferably by using <NUM>% TBP (tributyl phosphate) and <NUM>% DIBK (diisobutyl ketone) as the extractant, and Fe (III) as the co-extracting ion; and iron and lithium are back-extracted with water after the loaded organic phase is washed. NaCl is added to the stripping solution, and iron is extracted with TBP and diethylhexyl phosphate to achieve separation of iron and lithium. In the process, two extraction and stripping cycles are used, the iron is difficult to control during the operation, and DIBK has high water solubility and serious loss. In <NUM>, the Qinghai Salt Lake Research Institute of the Chinese Academy of Sciences used a tributyl phosphate-ferric chloride-kerosene system to conduct a scale-up test of lithium extraction from the brine of the Dachaidan Salt Lake, and obtained an anhydrous lithium chloride product with a purity of <NUM>%. In <NUM>, the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences and Qinghai Institute of Salt Lakes, Chinese Academy of Sciences studied the process of extracting lithium from Qinghai high-magnesium-lithium-ratio salt lake brine with a <NUM>% N235 (N,N-bis(<NUM>-ethylhexyl)acetamide)-<NUM>% TBP-<NUM>% sulfonated kerosene system, and the experiment results of the three-stage countercurrent extraction cascade showed that the extraction rate of lithium reached <NUM>%. Patent <CIT> provides a process for extracting lithium from salt lake brine to produce lithium carbonate. The extraction system includes an extractant, a co-extractant, and a diluent. The extractant is a phosphate ionic liquid containing functional groups for extracting lithium. The solution after extracting and degreasing is removed of magnesium with sodium carbonate and sodium hydroxide, and then subjected to lithium precipitation with sodium carbonate. The process uses dilute hydrochloric acid for back extraction, and the organic phase can be regenerated only by washing with pure water, which reduces the saponification and iron removal procedures, simplifies the process route, and greatly reduces the production cost.

At present, the extraction systems that have undergone industrial experiments or have been used in industrial production in China include amide extractant (N503, N523), neutral phosphine extractant TBP, and ketone extractant DIBK, which all need the addition of ferric chloride as a co-extractant, and the extraction with ferric chloride as a co-extractant must be carried out under acidic conditions to ensure the formation of FeCl<NUM>- and prevent the hydrolysis of Fe<NUM>+. In addition, the back extraction of Li+ requires a strong acid solution of above <NUM> mol/L which causes serious corrosion of the equipment, and emulsification occurs during the use of FeCl<NUM>. Iron is difficult to back-extract after it is combined with the organic. On the one hand, this will increase the organic density and viscosity, which causes it difficult to separate the phases (the salt lake lithium extraction usually uses a centrifugal extractor, which has high investment costs). On the other hand, this will reduce the organic loading.

<CIT> discloses an extraction solvent for extracting separating lithium element and a method for extracting separating the lithium element thereof, and belongs to the technical field of wet process metal metallurgy. An acid extracting agent or the mixture of the acid extracting agent and a neutral phosphorous extracting agent is taken as an extracting agent, and the lithium element in a solution containing lithium is extracted and separated by a saponated extracting agent to obtain a solution containing the lithium element. The extracting solvent and the method have the advantages that ferric chloride is not taken as a synergist, the application is wide, the obtaining of the extracting agent is easy, the investment is low, the cost is low, the use is convenient, safe and reliable, industrial production is convenient, the lithium element can be recovered from production waste water of lithium carbonate and the like, and the lithium element can be extracted from high-impurity and complex raw materials of high magnesium-lithium brine and the like. The solvent and the method are particularly suitable for extracting the lithium element in brine in China to help to improve the problems of low lithium resource grade, high separation difficulty, severe pollution and high cost in China.

Therefore, there is an urgent need to provide a method for recovering lithium in which an extraction system has good selectivity of lithium and sodium, high loading capacity and short process flow.

The objective of the present disclosure is to provide a method for recovering lithium from lithium-containing wastewater. The lithium-containing wastewater is sulfate raffinate wastewater produced during the recovery process of a ternary battery. The method for extracting lithium does not require the addition of ferric chloride as co-extractant, the extraction system has good selectivity of lithium and sodium, high loading capacity and short process flow, and the system enables good phase separation without the need of a centrifugal extractor, resulting in low equipment investment, which has a breakthrough significance in the battery recycling industry.

The invention is defined by appended claim <NUM>, preferred embodiments are defined in the dependent claims.

In order to achieve the objective mentioned above, the following technical solutions are used in the present disclosure:
A method for recovering lithium from lithium-containing wastewater, comprising the following steps:.

The feed liquid mentioned above is a sulfate system, in which it is found that using bis(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid and tributyl phosphate in combination to extract lithium-containing wastewater, the highest extraction rate is obtained.

Preferably, in step (<NUM>), the lithium-containing wastewater is sulfate raffinate wastewater after extraction of a nickel-cobalt-manganese ternary material.

In step (<NUM>), the Li+ concentration of the lithium-containing wastewater is <NUM>-<NUM>/L.

In step (<NUM>), the Na+ concentration of the lithium-containing wastewater is <NUM>-<NUM>/L.

In step (<NUM>), the organic phase consists of the following components by mass percentage: <NUM>%-<NUM>% of an extractant, <NUM>%-<NUM>% of a co-extractant and <NUM>%-<NUM>% of a diluent.

The extractant is bis(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid.

The co-extractant is tributyl phosphate.

In step (<NUM>), the saponifying agent used for saponifing the organic phase is sodium hydroxide.

In step (<NUM>), the saponified organic phase and the lithium-containing wastewater are in a volume ratio of <NUM>: (<NUM>-<NUM>) for extraction.

Preferably, in step (<NUM>), the amount of sodium hydroxide is <NUM>-<NUM> times the concentration of Li+ in the wastewater.

Preferably, in step (<NUM>), the extraction is conducted at a temperature of <NUM>-<NUM>, and the extraction lasts for <NUM>-<NUM>.

Preferably, in step (<NUM>), a rotation speed of shaking in the extraction is <NUM>-300rpm, and the shaking lasts for <NUM>-<NUM>.

In step (<NUM>), the extraction is multi-stage countercurrent extraction.

For a more thorough understanding of the present disclosure, preferred experimental schemes of the present disclosure will be described below in conjunction with examples to further illustrate the features and advantages of the present disclosure. The scope of protection of the present disclosure is defined by the scope of the appended claims.

A method for recovering lithium from lithium-containing wastewater was provided, comprising the following steps:.

The detection results of the content of lithium in the raffinate are shown in Table <NUM>. The single-stage extraction rate of lithium is <NUM>%.

The detection results of the content of lithium in the raffinate are shown in Table <NUM>. The extraction rate of lithium is <NUM>%.

Table <NUM> indicates that in an acidic environment, the higher the pH, the higher the extraction rate of lithium.

The detection results of the lithium content in the raffinate and the lithium content in the organic phase are shown in Table <NUM>. The total extraction rate of lithium is <NUM>%.

It can be seen from Table <NUM> that the higher the saponification factor, the higher the total extraction rate.

The difference between Example <NUM> and Comparative example <NUM> was that the organic phase was prepared from <NUM>% C272 (bis(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid) and <NUM>% sulfonated kerosene calculated by mass percentage.

The detection results of the content of lithium in the raffinate are shown in Table <NUM>.

The difference between Example <NUM> and Comparative example 1was that the organic phase was prepared from <NUM>% TBP (tributyl phosphate) and <NUM>% sulfonated kerosene calculated by mass percentage.

The test results of the content of lithium in the raffinate are shown in Table <NUM>. The extraction rate of calcium by this combined extractant is <NUM>%, and the extraction rate of Li by C272 (bis(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid) is <NUM>%, and the extraction rate of Li by TBP (tributyl phosphate) is <NUM>%.

It can be seen from the data in Table <NUM> that the extraction organic system is also suitable for the recovery of lithium in the hydrochloric acid system. The lithium extraction capacity of the organic phase for the two systems does not show significant difference, but the use of the hydrochloric acid system needs the addition of ferric chloride as a co-extractant, resulting in the occurrence of emulsification caused by the hydrolysis of Fe<NUM>+.

Claim 1:
A method for recovering lithium from lithium-containing wastewater, comprising the following steps:
(<NUM>) adjusting a pH of the lithium-containing wastewater to be <NUM>-<NUM>; and
(<NUM>) preparing and saponifying an organic phase successively, adding a saponified organic phase to the lithium-containing wastewater for extraction, and separating an aqueous phase to obtain a loaded organic phase containing lithium ions; wherein a solution for adjusting the pH of the lithium-containing wastewater is sulfuric acid; the organic phase comprises the following components: an extractant, a co-extractant and a diluent;
wherein, the organic phase consists of the following components by mass percentage: <NUM>%-<NUM>% of the extractant, <NUM>%-<NUM>% of the co-extractant and <NUM>%-<NUM>% of the diluent;
the extractant is bis(<NUM>,<NUM>,<NUM>-trimethylpentyl) phosphinic acid; the co-extractant is tributyl phosphate; the diluent is sulfonated kerosene;
a solution used for saponifying is sodium hydroxide;
the saponified organic phase and the lithium-containing wastewater are in a volume ratio of <NUM> : (<NUM>-<NUM>) for extraction;
the extraction is multi-stage countercurrent extraction;
wherein in step (<NUM>), the lithium-containing wastewater mainly comprises Li+, Na+ and SO<NUM><NUM>-; the Li+ concentration of the lithium-containing wastewater is <NUM>-<NUM>/L; the Na+ concentration of the lithium-containing wastewater is <NUM>-<NUM>/L.