Mineral liberation size

The particle size of the tungsten ore which determines the degree of disintegration necessary to liberate the tungsten mineral (liberation size). 

In contrast to minerals, the size-reduction process of solid wastes is relatively simple, as they are mostly composed of liberated materials. Also, the physical properties and mechanical characteristics of solid waste, which determine the... 

Beneficiation of tungsten ores by gravity was the classical method, followed by a cleaning step (Fig. 5.1). The recovery depends on the ore characteristics (mainly liberation size) and ranges typically between 60 and 85%. The main loss is in the slimes, because the tungsten minerals are the most fiiable ones present in ores. 

Consider wet processing for particle diameter <6 mm to minimize dusting and electrostatics. For particle diameter >150 pm, prefer wet belt <150 pm, prefer wet drum. Match magnetic gradient to the diameters of the particles. Match the machine to the liberation size (liberation size is 0.01 of the diameter of the mineral crystal). For wet machines, pump 4 Mg water/Mg sohds, although 90% of the water can be recirculated. 

For minerals, the liberation size is 0.01 of the diameter of the mineral crystal. 

Match magnetic gradient to the diameter of the particles. Match the machine to the liberation size (liberation size is 0.01 of the diameter of the mineral crystal, Section 5.18). 

Compared to the other flotation systems, the material is much coarser in potash flotation, due to a large liberalization size of the crystals. The rather small difference in density between the mineral salt and the brine makes it possible to float much larger particles in the brine system as compared to water systems. 

The beneficiation of raw potash ore into marketable products, similar to potash mining operations, requires a somewhat efferent scheme and equipment for each processing plant. The ore composition (mineralogy), ore grade (K2O content), liberation size (amount of masd-mum particle size required to attow separation of the different minerals), and type and amount of slimes (insolubles such as clay, anhydrite, dolomite, silica, etc.) are different for every deposit, and perhaps may be h W variable writhin a single deposit. Accordingly, themodr, ern potash processir plant must have an ef ient, hic y versatile process to accommodate variations in the feed yet still maintain product quality at as low a production cost as possible. 

A detailed laboratory study has been presented by Dresler et al. (1998) on the Roast, Acid-Leach Process that exactly follows the process previously used by the LCA (now EMC) at their North Carolina deposit. It is reviewed here because of the additional details that it supplies on this very effective spodumene process. Their ore was from Wekusko Lake, Manitoba, which as at LCA s deposit was an unzoned and low-grade (0.79% Li) spodumene ore, but with a very small crystal size. Electron micrographs showed that each of the minerals in the ore (Table 1.18) was present as discrete crystals, but the liberation size was quite small. Consequently, they ground the ore to a —212 p,m (—65 mesh) size, and made into a 23% slurry to be agitated and conditioned with 2 kg of sodium hydroxide/mt of ore for 20 min. 

The raw ROM (run of mine) ore is reduced in size from boulders of up to 100 cm in diameter to about 0.5 cm using jaw cmshers as weU as cone, gyratory, or roU-type equipment. The cmshed product is further pulverized using rod mills and ball mills, bringing particle sizes to finer than about 65 mesh (230 p.m). These size reduction (qv) procedures are collectively known as comminution processes. Their primary objective is to generate mineral grains that are discrete and Hberated from one another (11). Liberation is essential for the exploitation of individual mineral properties in the separation process. At the same time, particles at such fine sizes can be more readily buoyed to the top of the flotation ceU by air bubbles that adhere to them. 

Various techniques are available to separate the different types of particles that may be present in a sohd mixture. The choice depends on the physicochemical nature of the sohds and on site-specific considerations (for example, wet versus diy methods). A key consideration is the extent of the liberation of the individual particles to be separated. Particles attached to each other obviously cannot be separated by direct mechanical means except after the attachment has been broken. In ore processing, the mineral values are generally liberated by size reduction (see Sec. 20). Rarely is liberation complete at any one size, and a physical-separation flow sheet wih incorporate a sequence of operations that often are designed first to rejec t as much... 

The hberation of a valuable constituent does not necessarily translate direclly into recoveiy in downstream processes. For example, flotation tends to be more efficient in intermediate sizes than at coarse or fine sizes [Mclvor and Finch, Minerals Engineeiing, 4(1), 9-23 (1991)]. For coarser sizes, failure to liberate may be the hmitation finer sizes that are liberated may still be carried through by the water flow. A conclusion is that overgrinding should be avoided by judicious use of size classifiers with recycle grinding. 

FIG. 20-10 Fraction of mineral B that is liberated as a function of volumetric abundance ratio D of gangue to mineral B (1/grade), and ratio of grain size to particle size of broken fragments (1/Bneness). [ V egel and Li, Trans. Soc. Min. Eng.-Am. Inst. Min. Metall. Pet. Eng., 238, 179 (1967).]... 

Once the comminution process is completed, the succeeding operations in mineral processing are taken over by what is known as separation. Regardless of the method or methods used, the aim is always the same-to take a natural aggregate of minerals (an ore) and separate it into two or more mineral products. In general, the products of separation are (i) the concentrate which contains the valuable minerals and (ii) the tailings which contain primarily materials of little or no value. It may be borne in mind that minerals have been liberated, either by grinding or by chemical means, must usually be sized prior to... 

Separation processes, as could be seen from Figure 2.1, position themselves at the back end of the sequence in operations in the mineral processing flowsheet. The front-end operations has been found virtually to terminate with the liberation or the size-reduction processes involving crushing and grinding. It is important to limit the amount of size reduction to that at which adequate liberation is accomplished. The term adequacy is related to the cost involved in comminution and to performance of the concentration methods that follows. The concentration is obtained by separation processes which rely on differences in the properties of the particles, the physical and physico-chemical characteristics of minerals. In this context, it will only be relevant to refer to Table 2.5 which presents a summary of the processes along with the properties of the minerals that are exploited. 

Flotation is an important technique in mineral processing, where it is used to separate different types of ores. When used to separate solid-solid mixtures, the material is ground to a particle size small enough to liberate particles of the chemical species to be recovered. The mixture of solid particles is then dispersed in the flotation medium, which is usually water. The mixture is then fed to a flotation cell, as illustrated in Figure 8.12a. Here, gas is also fed to the cell where gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid particles are collected from the surface by an overflow weir or mechanical scraper. The separation of the solid particles depends on the different species having different surface properties such that one species is preferentially attached to the bubbles. A number of chemicals can be added to the flotation medium to meet the various requirements of the flotation process ... 

In general, the run-of-mine ore is composed of quartz and silicates, 40-50%, and sulphides (pyrite, marcasite, pyrrhotite and arsenopyrite). The principal tin mineral is cassiterite, with minor amounts of stannite. Based on liberation studies, a large portion of the tin is liberated at 300-400 pm size. A portion of the tin is liberated at-12 pm size. The generalized gravity concentration flowsheet is shown in Figure 21.9. 

A large hard rock rutile deposit was discovered in central Chile. This ore is relatively complex with variable head grade of rutile ranging from 2% to 4% Ti02. The liberation of rutile occurs at about 100 mesh nominal size. The major gangue minerals present in this ore include feldspars, calcite and some silicates. 

Materials mined from a mineral deposit usually consist of a heterogeneous mixture of solid phases that are generally crystalline and contain various minerals. Crushing and grinding operations are used to liberate the mineral species from one another and to reduce the size of the solids to a range suitable for subsequent processing. Of the various separation techniques, those of froth flotation and agglomeration exploit the chemical and physical properties of the surfaces of minerals, which can be controlled by various chemical interactions with species in an aqueous phase. 

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