Lepidolite deposits

Lepidolite is a lithium potassium mica it also belongs to the class of aluminum silicates. Various empirical formulas have been proposed for it, probably because its actual composition varies somewhat. In fact, none of these minerals are pure crystals of definite composition. Of the lepidolite deposits which have been discovered in the United States so far, none warrant mining today. Lepidolite is processed in the United States, but the ore is imported from southern Africa. 

In the early lithium operations prior to 1960 a 610 m adit was used to enter underground workings in the lepidolite deposit at the 61 m level. Cars were loaded through overhead chutes, and then hauled by diesel locomotives to the beneficiation plant 450 m from the adit. The ore was crushed to about a — 76 mm size and screened, the waste removed by hand sorting from a conveyor belt, and the waste and fines stockpiled for potential future use. The concentrates were often of almost mineral collector s appearance, and they were trucked to the port at Beira for overseas shipment, and later delivered by the Rhodesian Railways. Petalite was mined in an open pit, and also hand sorted, but amblygonite was only obtained by selective hand mining in outcrop areas (Kesler, 1960). 

Cesium, an alkali metal, occurs in lepidolite, pollucte (a hydrated silicate of aluminum and cesium), and in other sources. One of the world s richest sources of cesium is located at Bernic Lake, Manitoba. The deposits are estimated to contain 300,000 tons of pollucite, averaging 20% cesium. 

The element is much more abundant than was thought several years ago. It is now considered to be the 16th most abundant element in the earth s crust. Rubidium occurs in pollucite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of the oxide. It is found in lepidolite to the extent of about 1.5%, and is recovered commercially from this source. Potassium minerals, such as those found at Searles Lake, California, and potassium chloride recovered from the brines in Michigan also contain the element and are commercial sources. It is also found along with cesium in the extensive deposits of pollucite at Bernic Lake, Manitoba. 

Numerous processes have been proposed for extracting potash from felspar, leucite, alunite, and other minerals rich in this substance, but the cost is so great that very few proposals yet made ofier promise of successful competition with the Stassfurt deposits. This is even the case with alunite, where mere calcination to 1000° drives off water and sulphuric acid, leaving water-soluble potassium sulphate, and alumina. Humphry Davy in his paper On Some Chemical Agencies of Electricity (1807), indicated in Cap. Ill, found that when water was electrolyzed in cavities contained in celestine, fluorspar, zeolite, lepidolite, basalt, vitreous lava, agate, or glass, the bases separated from the acid and accumulated about the cathode. It is therefore probable that if water with finely divided potash minerals in suspension were electrolyzed, the alkali would be separated in a convenient simple way. 

Occurrence.—Rubidium is widely distributed in nature, being found in small quantities in association with the other alkali-metals. It constitutes about 1 per cent, of lepidolite, and is present in the Stassfurt salt deposits, in the soil, in many natural waters, and in the ashes of numerous plants. 

The most important mineral for the industrial extraction of lithium is spodumene (LiAlSi206), which is found together with lepidolite, petalite and amblygonite (all with Li contents of 4 to 7%) and in salt lakes. The largest known reserves are in Chile (largest known deposit), Australia, USA and Canada. The main producer countries are the USA (North Carolina), Chile, Australia, Russia, Zimbabwe, Brazil and China. The worldwide reserves including the lithium content in salt lakes is estimated to be 7.3 10 t (as lithium), of which 60% is in salt lakes. 

Like the other alkali metals, cesium is a soft, silvery metal, but it appears golden if it has been exposed to small amounts of oxygen. It is not found in its metallic state in nature it is obtained as a byproduct of lithium processing of the mineral lepidolite. Its most significant ore is pollucite, and the world s largest pollucite deposit is found in Bernic Lake, Manitoba, Canada. Cesium s average crustal abundance is about 3 parts per million. Cesium is the most electropositive stable element and will ignite if exposed to air. Cesium burns blue in the flame test. 

Lepidolite. A lithium mineral, approximating to LiKAIp2Si304 sp. gr. 2.9 m.p. 1170 C. The largest deposits are in Rhodesia but it also occurs in USA the average Li20 content is about 4%. Lepidolite is a source of Li for special glasses, pottery bodies and glazes, and vitreous enamels account must be taken of its F content. 

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