Refractory ores

Chlorination and fluorination, as processes of metal extraction, are important not only because they are effective in liberating metal values from refractory ores but also because the chlorides and the fluorides are excellent interprocess intermediates for metal reduction. The chlorides have the additional advantage of being compounds which may be made very pure by certain additional processes. 

Gold ores grouped as refractory are those in which the gold does not lend itself easily to dissolution in cyanide solutions. There are at least three different types of refractory ores that are encountered ... 

APOL [Alkaline pressure oxidation leaching] A process for extracting gold from refractory ores, developed by Davy McKee (Stockton, UK). 

Effect of amine-modified C11SO4 on gold-bearing sulphide flotation from carbonaceous refractory ore... 

Baum, W., Mineralogy as a Metallurgical Tool in Refractory Ore, Progress Selection and Optimization, Randol Gold Forum, Squaw Valley, 1990. 

This ore type belongs to the refractory ore type, found in Egypt and North Africa. 

There are several fairly large niobium deposits around the world that belong to the refractory ore type. Some of these deposits can be found in Brazil, Africa and Greenland. Typically, these ores are heavily oxidized and mostly contain iron oxides and aluminium silicates. A typical example of such a deposit is the Mrima Hill deposit found in southeast Kenya, which was a case study in which new technology was examined. 

Locked-cycle test results obtained from the Mrima Hill niobium refractory ore... 

The National Science Foundation is funding research at the South Dakota School of Mines, Rapid City, South Dakota, to develop an alternative approach to the extraction of precious metals from refractory ores which will pose a much lesser threat to environmental quality than the presently predominant cyanide leaching process. 

Shallow, L.J. (1999) Refractory ores at the Rain Mine, Elko County, Nevada structural controls, wallrock alteration, petrography and geochemistry. Master s Thesis, University of Nevada, Reno, NV. 

BIOPRO A biological process for leaching gold from refractory ores. Developed by Newmont Mining. 

The smelting process consists in the formation of an alloy of gold with silver and lead, and is similar to that employed in extracting silver. It is applicable to ores rich in silver, and also to refractory ores containing arsenic and antimony, for which the other processes are unsuitable. 

There is currently much interest in the use of microorganisms to recover toxic or valuable metals from solution and to extract metals from low-grade or refractory ores. In both cases, the availability of this new technology depends upon the exploitation of natural processes in which microorganisms cause the deposition or the solubilization of minerals. 

There has also been some interest in heap leaching of low-quality refractory ores. This is a two-stage process, as bacterial leaching of the ore must be followed by leaching with alkaline cyanide to solubilize the gold. The heap must also be washed and neutralized before the cyanide leach can be applied (103). 

Lorenzen, L. van Deventer, J.S.J. (1992b). The mechanism of leaching of gold from refractory ores. Minerals Engineering, 5, 1377-1387. doi 10.1016/0892-6875(92)90173-7... 

The Bayer process has similarly experienced significant change in recent years. It is an excellent example of large-scale, nonoxidative pressure leaching. Changes in Bayer process technology have resulted mainly from the need to treat more refractory ores. Bauxite ore types are important since the difficulty of digestion depends on the form of the hydrated aluminum oxide present. Aluminum in bauxite usually exists in one of three forms ... 

Concentrated acids are usually only employed for refractory ores which do not respond to less severe breakdown techniques, and for the same reason might be expected to be used at fairly high temperatures. If cost, availability, and plant corrosion did not already provide sufficient grounds for a choice of sulphuric acid, its higher boiling-point than other acids would usually do so. 

Sodium hydroxide is used, either in the molten condition (m.p. 318X) or as a concentrated solution at about 200°C, for the breakdown of refractory ores such as phosphates or silicates. Usually, the oxide, hydrated oxide or hydroxide of the metal is produced and this can be dissolved in dilute acid for further purification, after first washing free from the other... 

Southern Greenland is known to contain a huge natural stock of uranium in low-grade material from which extraction is difficult and recovery poor (the so-called refractory ores). It is related to alkaline intrusion. 

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