Siliceous zinc ores

I.G. Matthew and D. Eisner, The Hydrometallui ical Treatment of Siliceous Zinc Ores , USPat.3.656.941.18 April 1972, (EZ Co.of Australasia Ltd.). 

BEirmiEU, who hasmade numcrons experiments on the subject of the assay of zinc ores, divides the latter into four classes, for each of which a particular method must be pursued. These are, firstly, ores in which the zine exists as oxide, or carbonate of tjie oxide -secondly, those in which tho zinc exists wholly C in part as silicate of the oxide thirdly, ores in which the zinc is entirely or in part in the form of sulphide and fourtidy, alloys of zinc. 

Further investigations were carried out over a large lead-zinc ore body in China, in which ore zones occur in both flanks of a reverse anticline. The ore is richer in the eastern flank, where it is controlled by an interlayer breccia zone. Smaller amounts of ore occur in fractures and fissures in siliceous limestone. The ore body is buried beneath 350 m of barren rock in the south and warps up northward, where it is buried beneath 250 m of barren rock.. The ore is richer in the north than in the south. The hangingwall rocks are conglomerates and red-bed sediments, in which interstitial water is abundant. The topography of the area is mgged. The soil is brick red and 0.8 to 10 m thick. 

H.L. Radino and Companhia Mercantil e Industrial Inga, Process of Zinc Extraction from Zinc Ores Comprising Soluble Silicates by Means of Hydrometallurgy , Australian Pat.224.195. 31 May 1957. 

Direct treatment of oxide, silicate and carbonate zinc ores is difficult if conventional zinc technology is used (leaching, purification by means of cementation with zinc powder and zinc electrowinning). There is only one case (Padaeng, Thailand) where conventional zinc flowsheets were successfully modified to treat zinc silicate ores. This was possible given the high-grade zinc ore treated (30% Zn) and the fact that this plant was able to solve Ae solid-liquid separation problems. 

The Angouran mine is a very well known mine which has been exploited only at low capacities. The Angouran deposit is located in northwest Iran and is comprised of oxidized zinc ores, mainly carbonates and silicates. 

Elemental zinc was officially discovered in Enrope in 1746 when calamine (zinc silicate) was rednced with charcoal to produce the metal. However, zinc had been used for many hundreds of years before tMs discovery because zinc ores and copper ores were used to form copper-zinc brass alloys. The main sources of zinc are ores composed of sphalerite (ZnS), smithsonite (ZnC03>, and an oxide mixture of zinc, iron, and manganese called franklinite. These ores are roasted to form the oxides of the metals and then reduced with carbon to produce the elemental metals. Zinc combines with many different metals to form useful alloys. As we have seen, the combination of zinc and copper produces the brass family of alloys. The combination of zinc and nickel with copper produces alloys with a silver color called German or silver brass. Zinc is also used in solder alloys with low melting points. 

The principal ores of zinc are sphalerite (sulfide), smithsonite (carbonate), calamine (silicate), and franklinite (zine, manganese, iron oxide). One method of zinc extraction involves roasting its ores to form the oxide and reducing the oxide with coal or carbon, with subsequent distillation of the metal. 

Zinc (76ppm of the earth s crust) is about as abundant as rubidium (78 ppm) and slightly more abundant than copper (68 ppm). Cadmium (0.16 ppm) is similar to antimony (0.2 ppm) it is twice as abundant as mercury (0.08 ppm), which is itself as abundant as silver (0.08 ppm) and close to selenium (0.05 ppm). These elements are chalcophiles (p. 648) and so, in the reducing atmosphere prevailing when the earth s crust solidified, they separated out in the sulfide phase, and their most important ores are therefore sulfides. Subsequently, as rocks were weathered, zinc was leached out to be precipitated as carbonate, silicate or phosphate. 

C21-0078. The only important ore of mercury is cinnabar, HgS. In contrast, zinc is found in several ores, including sulfides, carbonates, silicates, and oxides. Explain these observations in terms of hard and soft acids and bases. 

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Zinc is a bluish-white, lustrous metal which tarnishes in air. It is present in the earth s crust as sulfide (sphalerite), carbonate, or silicate ores, to the extent of only 78 ppm, making it the 23rd most abundant element.2 The metal is obtained from its ores by roasting and subsequent reduction with coke or by electrolysis. Approximately 8.36 million metric tons of zinc were produced worldwide in 2002 of this amount, two-thirds were from ores, while one-third was obtained from recycled zinc.3 The ease of mining and refining of the ore and the subsequent low price of the metal (ca. 1.2 kg-1 in 1998)3 have made zinc the third most popular non-ferrous metal (after aluminum and copper). 

The mixed willemite-smithsonite ore has the simplest mineral composition of the three basic ore types. The silicate, goethite and barite are the principal gangue minerals. Will-emite is a major zinc oxide mineral present as free crystals ranging from 50 to 500 pm in size. Smithsonite is usually stained with Fe-hydroxides and sometimes is associated with silicate as inclusion and/or attachments. The barite content of the ore may vary from several percent up to 12%. A few deposits of this ore type are found in Mexico and South America. 

In a letter to the Annals of Philosophy, dated Cambridge, February 18, 1820, Edward Daniel Clarke wrote as follows Some varieties of radiated blende from Przibram in Bohemia are described by Stromeyer as containing two or three per cent of cadmium. At a sale. .. in London, I procured specimens of the particular mineral thus alluded to, which were sold under the name of splendent fibrous blende from Przibram, pronounced Pritzbram. I found afterwards that they had been brought to England by Mr. J. Sowerby of Lisle-street, a dealer in minerals.. . . Upon my return to Cambridge, I endeavoured to obtain cadmium from this ore, and succeeded. . . (133). Clarke also found this element in die zinc silicate from Derbyshire, England, and his results were soon confirmed by W. H. Wollaston and J. G. Children. In 1822 Clarke published a paper on the presence of cadmium in commercial sheet zinc (134). 

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