Know How Lithium Mining Process Is Carried Out
26 July, 2017
For many years, the commercial production of lithium was dependent on mineral ore sources like lepidolite, petalite, and spodumene. Extracting the metal from these ores proved to be more expensive than actually extracting it from lithium-containing brines. As a matter of fact, it would cost you double to extract lithium from hard rock than it would from brines. That is why most lithium sources have been kicked out of the market in last two decades. Salar brines are underground reservoirs containing dissolved salts in very high concentrations. These salts include sodium, potassium, and lithium. You will generally find them in salars, which are surfaces below dried lakebeds.
The Lithium Mining Process
Before lithium is extracted from brines, this salt-rich water is pumped out to the surface. It is directed into a number of ponds for solar evaporation to take place, a process that could take several months to complete. Since salar brines are naturally found low rainfall, high altitude areas, solar evaporation is the most cost-effective and ideal way to precipitate these salts. The first salt to harvest from the ponds is potassium, which can be found in first ponds. Later ponds contain high lithium concentrations. Economically-viable lithium brines must contain several hundred parts ppm (parts per million) of the metal, sometimes up to 7000 parts per million.
Upon reaching an optimum concentration, the lithium chloride in the evaporation ponds has to be pumped into a recovery plant for filtration as well as extraction in order to get rid of all unwanted boron and magnesium. It is after this that the remainder is reacted with soda ash (sodium carbonate). This process helps precipitate lithium carbonate. It is then filtered and dried, after which it can now be perfectly delivered. Any excess residual brine collected in the process will have to be pumped back into salars.
Generally, this lithium carbonate, in form of white powder, is important intermediary because it is easily converted into industrial chemicals and salts. It can also be processed or converted into the lithium metal.
Extracting lithium from other minerals including spodumene, unlike from salar brine, is a complex process that will require the completion of several hydrometallurgical processes. That explains its higher cost. The ore is first crushed and heated in a rotary calcining kiln. This helps in converting the metal’s crystal phase to beta from the initial alpha phase in a process known as decrepitation. This method allows sodium to displace all the lithium in the core. The resultant spodumene concentrate undergoes a cooling and milling process to form fine white powder. This powder is then mixed with sulphuric acid and again roasted. To separate any waste from this concentrated solution, while precipitating out any calcium or magnesium from the solution there is need to use filter system and thickener. The final stage entails adding soda ash (or sodium carbonate) to crystalize the lithium carbonate. It is then heated, filtered and dried. The end product is 99 per cent pure lithium carbonate.
Conversion of the Carbonate into a real Metal
The entire conversion process is done using lithium chloride placed in an electrolytic cell. The next step involves thoroughly mixing lithium chloride with potassium chloride in an 11: 9 ratio. This process produces a eutectic electrolyte in molten form. To help in increasing the conductivity of lithium and at the same time lower its fusion temperature, potassium chloride is added to the electrolyte. Upon fusion and electrolysis at about 450 degrees Celsius, lithium in molten form, rises to the surface and collects in cast iron enclosures while chlorine gas is allowed to escape. To prevent oxidation and any damage from other atmospheric elements, the pure lithium metal extracted is enfolded in paraffin wax. This conversion from lithium carbonate to pure lithium metal has been found to have a conversion ratio of about 5.3:1.
Australia and Chile are the largest sources of lithium in the world. However, China, Argentina and the US are also major producers. Lithium carbonate is usually sold by miners to refiners on three- to five-year contracts. The miners then go ahead with the process of producing and marketing the lithium metal and downstream chemicals.
The US Geological Survey estimates the world’s lithium production at more than 37,000 metric tonnes. Most of it is used as chemicals and salts while only about ten per cent of it undergoes electrolysis for use as a metal. Lithium recycling has grown remarkably since the setting up of a lithium-ion battery recycling plant in Japan in 1992. More plants have since been set up in Canada, the US, Japan, Germany, and Belgium. These countries all process batteries to extract lithium and other components from them.