Leaching acidity

Most U.S. production (20 x 10 lbs ia 1996) of primary vanadium compounds has been as by-products or coproducts of uranium and of ferrophosphoms derived from smelting Idaho phosphates. Most of this processiag was from leaching acids, residues, and spent catalysts. The only domestic commercially mined ore, for its sole production of vanadium, is Arkansas brookite. It has contributed significantly to domestic supply siace ca 1969, however, it has not been mined siace 1992 (25). 

In the study of soil science, most attention has historically been paid to the aluminosilicate clays, which dominate the properties of temperate soils, the first to be scientifically studied. More recently, the importance of the amorphous aluminosilicates has been shown in young soils, in soils derived from volcanic ash and in leached, acidic soil (e.g. podzols or spodosols). The hydrous oxides are especially important components of old, highly weathered soils, such as those found in the tropics (e.g. oxisols). This is an important distinction as the charge on the aluminosilicate clays is predominantly a permanent negative charge, while the amorphous aluminosilicates and hydrous oxides have a variable,... 

Alfisols Forest soils of humid and subhumid climates with strongly leached acidic A horizon con-... 

Ultisols Strongly-leached acidic A and E horizons over well-developed, kaolinite-rich (base-poor)... 

Ultisols. Mineral soils that have an argillic horizon with a base saturation of <35% when measured at pH 8.2. Ultisols are strongly leached, acid forest soils with relatively low native fertility. They are found primarily in humid temperate and tropical areas of the world, typically on older, stable landscapes. These soils are characterized by an accumulation of clays in the subsurface horizon and exhibit strong yellowish or reddish colors resulting from the presence of iron oxides. Ultisols are divided into five suborders Aquults, Humults, Udults, Ustults, and Xerults. 

Percolation leaching may also be regarded as a partially counter-current process. In its simple form the process involves the passing of the leaching acid down a column, or through a bed, of ore which has been ground to a suitable particle size. A suitable grid or filter medium is used as a support... 

Iron minerals and tramp iron introduced from the crushing and grinding stages can often be removed conveniently before leaching by electromagnetic separation. This has been shown to result in substantial economies in the use of leaching acid when the grade of ore is of the same order as, or even less than, the iron content. 

The breakdown of an ore with a concentrated acid, on an industrial scale, is only justified if the mineral values are fairly high in concentration and of some economic importance. A high acid wastage upon unwanted minerals, e.g. carbonates, oxides, sulphates, phosphates and silicates, can normally be expected if these are present, and in any case the quantity of acid required merely to wet the ore and form a workable pulp is of necessity high. Corrosion problems are generally more severe than with dilute leaching acids and require more expensive materials of construction. 

Various continuous leaching processes have also been employed. Usually the powder and leaching acid are fed in a co-current manner into a rotating or stirred vessel and at some point it is necessary to separate the resulting metal powder under conditions where it is not allowed to remain static for long periods. The complexity of a safe continuous system, coupled with the relatively small scale of operation, usually leads to a preference for a batch leaching system. 

Search Minerals Inc., 1320 - 885 West Georgia Street, Vancouver, Canada V6C 3E8 Keywords Nickel, Cobalt, Atmospheric Leaching, Acid, Saprolite, Caron Plant, SALT... 

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