Magnesium sulfate from lithium brines

Great Salt Lake, Utah, is the largest terminal lake in the United States. From its brine, salt, elemental magnesium, magnesium chloride, sodium sulfate, and potassium sulfate ate produced. Other well-known terminal lakes ate Qinghai Lake in China, Tu2 Golu in Turkey, the Caspian Sea and Atal skoje in the states of the former Soviet Union, and Urmia in Iran. There ate thousands of small terminal lakes spread across most countries of the world. Most of these lakes contain sodium chloride, but many contain ions of magnesium, calcium, potassium, boron, lithium, sulfates, carbonates, and nitrates. 

The worldwide production of lithium in aU forms was 21,1001 in 2006 (see Ref 27, p. 96). Lithium sulfate solutions are obtained by treating certain ores with sulfuric acid. Lithium is also produced from certain brines that have a low magnesium content. In both cases, adding carbonate precipitates lithium carbonate. Mixing a lithium carbonate slurry with calcium hydroxide produces lithium hydroxide, and lithium hydroxide monohydrate is crystallized from the supernatant solution. Lithium hydroxide is the least soluble alkali metal hydroxide, with a maximum concentration of... 

Brine can be pumped from the Salar s near-surface salt mass at relative high rates, such as >31.5 liter/sec (500-1000 gpm) without appreciable draw-down, although such high pumping rates would hasten the short-circuiting of brine from nearer the surface and from other areas of the Salar. The brine is saturated with salt, and contains variable concentrations of lithium, potassium, magnesium, sulfate and borate in different locations in the Salar (Tables 1.5 and 1.6 Fig. 1.12). The lithium concentration varies from about 1000-4000 ppm, and averages over 1500 ppm for the two commercial operations on the Salar. The total lithium... 

A third source of brine is found underground. Underground brines ate primarily the result of ancient terminal lakes that have dried up and left brine entrained in their salt beds. These deposits may be completely underground or start at the surface. Some of these beds ate hundreds of meters thick. The salt bed at the Salat de Atacama in Chile is over 300 m thick. Its bed is impregnated with brine that is being pumped to solar ponds and serves as feedstock to produce lithium chloride, potassium chloride, and magnesium chloride. Seades Lake in California is a similar ancient terminal lake. Brine from its deposit is processed to recover soda ash, borax, sodium sulfate, potassium chloride, and potassium sulfate. 

The main metals in brines throughout the world are sodium, magnesium, calcium, and potassium. Other metals, such as lithium and boron, are found in lesser amounts. The main nonmetals ate chloride, sulfate, and carbonate, with nitrate occurring in a few isolated areas. A significant fraction of sodium nitrate and potassium nitrate comes from these isolated deposits. Other nonmetals produced from brine ate bromine and iodine. 

Chemicals from brine, 5 784-803 calcium chloride, 5 793-795 iodine, 5 795—796 lithium, 5 796-797 magnesium compounds, 5 797-798 minerals from brine, 5 790-793 potassium compounds, 5 798-799 recovery process, 5 786-790 sodium carbonate, 5 799-800 sodium chloride, 5 800-801 sodium sulfate, 5 801-802 Chemicals Guideline, integrated,... 

Lithium may be recovered from natural chloride brines. Such recovery processes may require additional steps depending on the magnesium and calcium content of the brine. The process involves evaporation of brine, followed by removal of sodium chloride and interferring ions such as calcium and magnesium. Calcium is removed by precipitation as sulfate while magnesium is removed by treating the solution with lime upon which insoluble magnesium hydroxide separates out. Addition of sodium carbonate to the filtrate solution precipitates hthium carbonate. 

From the final pond the concentrated brine (Table 1.3) with a density of about 1.25 g/cc was pumped nearly 4.8 km (3 mi 1.5 mi in 1967, Gadsby, 1967) to the processing plant in the town of Silver Peak. The plant had been converted from a silver ore cyanide-leach plant that had operated there from 1864-1961. In the conversion all of the tanks and settlers were rubber lined to reduce iron contamination in the product, and considerable new equipment was added. The solar pond brine was first reacted with lime to remove most of the residual magnesium and some of the sulfate and borate ions, and then a small amount of soda ash was added to precipitate most of the calcium from the lime reactions. The slurry from these operations was settled and filtered, and the overflow solution sent to storage tanks. From there the brine was pumped through filter presses to be totally clarified, and then heated to 93°C (200°F lithium carbonate has an inverse solubility) and reacted with dry soda ash and hot wash and make-up waters to precipitate the lithium carbonate product. Extra water was added to prevent salt from crystallizing, since the pond brine was samrated with salt. The lithium carbonate slurry was thickened in a bank of cyclones, and the underflow fed to a vacuum belt filter where it was washed and dewatered. The cyclone overflow and filtrate were... 

Brine from the sylvinite ponds next went to the camallite ponds (Fig. 1.64), and from there to the 500,000 m bischoffite ponds (Fig. 1.65). These two series of lithium ponds were also periodically taken out of service to harvest predominantly camallite from the first ponds, and bischoffite from the later ponds. These minerals were stockpiled separately, with some of the bischoffite sold as magnesium chloride (with a capacity of 450,000 mt/yr), and the camallite saved for later conversion to potash. The six camallite ponds were divided into two groups of three, with the higher sulfate brine directed to one group, and then its end-liquor was returned to the Salar by being flooded onto its porous surface. The final brine from the bischoffite ponds contained 6.0-6.1% Li, and was sent to 40,000 m, about 3 m deep holding ponds to await tmck shipment to the lithium carbonate plant. The plant had a capacity of 22,000 mt/yr of Li2C03 in 2002, to be raised to 28,000 mt/yr in 2003 (Moura, 2002 Etchart, 2002 Nakousi, 2003). 

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