Lithium mainly exists in two forms in nature, one is in the form of lithium ore (mainly spodumene, lepidolite, lithium feldspar, etc.) . It exists in the form of lithium ions in various brines (including salt lakes, groundwater and seawater). According to statistics, there are about 350 million tons (LCE) of ore lithium resources and 1.3 billion tons (LCE) of salt lake brine lithium resources in the global proven reserves of lithium resources.
According to the different types of lithium resources, the extraction process is also different. The main extraction processes are introduced as follows:
1. Extraction technology
for lithium ore Calcination-sulfuric acid leaching
uses spodumene as raw material to produce lithium carbonate by calcination transformation and sulfuric acid leaching, which is the most widely used and mainstream production mode in the world. At the same time, it is also a relatively mature process in industry. The spodumene concentrate is roasted at a high temperature in a rotary kiln, and is subjected to ball milling, sufficient sulfuric acid mixing and roasting after cooling, and then is subjected to water leaching, and sodium is added to precipitate into lithium carbonate after impurity removal. The
sulfate mixed sintering method
comprises the following steps of: mixing and sintering lithium ore and sulfate, dissolving the sintered clinker, removing impurities from the obtained solution taking lithium sulfate and potassium sulfate as main components, filtering, evaporating and separating to obtain a lithium sulfate solution, and adding sodium carbonate to precipitate lithium carbonate to obtain a lithium carbonate product. After the
sodium carbonate is pressurized, leached
and activated, the lithium ore and the sodium carbonate are proportioned, boiled and dissolved, and finally the lithium is separated and recovered by lithium precipitation. The operation of the process is simple and the recovery rate is high.
Limestone roasting method Lim
estone sintering method is to mix limestone and other raw materials with lithium ore according to a certain mass ratio, sinter, leach with water, filter to obtain lithium leaching solution, realize the separation of calcium, aluminum, silicon and other impurities in minerals, and then purify to obtain lithium hydroxide solution. The lithium product can be obtained by concentrated crystallization or carbonization.
2. The extraction technology
of salt lake brine can be divided into sulfate salt lake, chloride salt lake, carbonate salt lake and nitrate salt lake according to the type of salt lake. Correspondingly, the process of lithium extraction is also quite different. The main extraction process is as follows:
The brine containing lithium is naturally evaporated and concentrated by the concentration-conversion method
. When the lithium content reaches an appropriate concentration, the separation processes such as boron removal, magnesium removal and calcium removal are carried out, and then soda ash is added to precipitate lithium in the form of lithium carbonate. The process has the advantages of simple process, low energy consumption and low cost, and is suitable for the brine with low alkaline earth metal content and low magnesium-lithium ratio.
The production process of
solid phase calcination method is a technology for extracting lithium from salt lake brine with high ratio of magnesium to lithium. Firstly, the salt lake brine is subjected to salt pan evaporation, salt precipitation and concentration, and then heated and evaporated to obtain a solid phase containing LiCl. The solid is calcined at high temperature, and then the calcined sinter is leached with water. Because the lithium salt is easily soluble in water, it is transferred into the solution. The magnesium oxide obtained by the conversion of magnesium chloride calcined at high temperature is almost insoluble in water, so it remains in the calcination residue. The separation of magnesium and lithium is achieved by calcination and leaching processes. And then treat that leaching solution to remove impurity such as sulfate radicals, a small amount of magnesium, boron and the like in the leaching solution, purifying the filtrate, evaporate and concentrating the filtrate, and precipitating the filtrate by adopting a sodium carbonate method to obtain the lithium carbonate. The
solvent extraction method
comprises the following steps of: performing salt pan solarization on salt lake brine, separating out sodium chloride, carnallite and part of bischofite step by step, acidifying the obtained concentrated brine, feeding the acidified concentrated brine into an extraction tank, performing multi-stage countercurrent extraction washing, back extraction, acid washing and the like, The obtained back extraction liquid is subjected to evaporation concentration, roasting, leaching and impurity removal in the finished product process, and then subjected to evaporation concentration and soda ash precipitation to prepare a lithium carbonate product.
Adsorption
method The production process of adsorption method first uses selective adsorbent to adsorb lithium ions in brine, and then elutes lithium ions, so as to separate lithium ions from other ions, which is convenient for conversion and utilization in subsequent processes. The concentrated brine containing lithium obtained by solarization and evaporation of the salt pan by
the electrodialysis method
is subjected to circulation (continuous type, continuous partial circulation type or batch circulation type) process concentration of lithium by using anion and cation monovalent selective ion exchange membranes through a one-stage or multi-stage electrodialyzer to obtain the lithium-rich low-magnesium brine. Then the lithium carbonate product can be prepared by deep impurity removal, refining and concentration, conversion and drying. Gradient extraction of lithium
from
solar pond is to evaporate the brine at low temperature in winter to remove a large amount of mirabilite and natron in the brine, so that the lithium element in the brine can be rapidly enriched. Lithium carbonate is then extracted using the solar pond process. The method for preparing the lithium salt
from the sulfate type salt lake brine on the
plateau comprises the following steps of: evaporating the sulfate type salt lake brine to a sodium chloride saturated state, freezing in winter to separate out mirabilite, and evaporating the brine after the mirabilite is separated out in spring and summer to separate out sodium chloride; The method comprises the following steps: naturally evaporating the brine from which sodium chloride is separated to remove impurities to obtain the brine with high magnesium chloride content; mixing the brine with high magnesium chloride content with mirabilite to react to separate out sodium salt and magnesium salt until the brine is rich in boron and lithium; evaporating the brine rich in boron and lithium until the content of boron or lithium reaches a preset value, and mixing the brine with water or the original brine to react to separate out boron ore; and performing solid-liquid separation to obtain the lithium-rich brine.
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