Starting with a mixture of any of the above minerals it may be determined whether or not they can be separated byhigh tension, magnetic, or gravity methods and whether any one, or a combination of Electromagnetic Separation methods is required. If the minerals appear in different columns they may be separated by high tension and/or magnetic methods alone. Two or more minerals appearing in the same column can be separated by gravity concentration if they have sufficient difference in gravity (usually a difference of approximately I.O).
It should be noted that grain shape and/or size may alter separation characteristics. This is sometimes a detriment and other times useful. As an example, mica and quartz may in many cases be separated by high tension due to their grain shape.
Minerals behaviour characteristics shown are from tests made in our laboratories rather than theoretical. Mineral characteristics and behaviours sometimes vary from different deposits. The behaviour of minerals not shown can usually be predicted by the behaviour of similar minerals in the belowtable.
Magnets of the suspended or magnetic pulley type are often advisable for use with continuous pilot test plants as the occurrence of such foreign materials as tramp iron are not unusual in ore being testedon a large scale. The use of magnets will frequently prevent otherwise expensive and troublesome breakage in the crusher or damage to crushing rolls, with resultant shutdown and loss of testing time.
The (Suspended Type) Laboratory Magnet is usuallyplaced above the ore conveyor preceding the jaw crusher. Width of conveyor belt, depth of ore being conveyed and average percent of foreign material to be eliminated determine the size of magnet required. This type magnet isfurnished either circular or rectangular.
The high intensity (Pulley Type) Laboratory Magnet is one of the most practical, satisfactory, and economical magnets in use today. Used as the head pulley of a conveyor, the shaft of the magnetic pulley can very often be made to correspond with the shaft of the original pulley. It is only necessary then to place the magnetic pulley into the existing bearings. Magnetic pulleys are wound for either 110 or 220 volts and are furnished for direct current only. Rectifiers are available to enable use of alternating current. Let us make recommendations for your continuous laboratory or pilot test plant.
The Alnico Horseshoe Laboratory Magnet is a small extremely powerful hand magnet. It is an alloy of aluminum, nickel and cobalt, and is many times stronger than the ordinary horseshoe magnet. It is extremely resistant to demagnetization and is affected only slightly by shock or temperatures as high as 1200F. This magnet provides an invaluable tool for the assayer, mineralogist, andtest plant operator. Minerals that are even moderately magnetic may be separated from non-magnetic material with this magnet and it is small and light enough to carry about in your pocket.
The Dings (Rowand-Wether- ill)Magnet Separator (CrossBelt Type) is a super-highintensity machine for feebly magnetic materials. It finds its principal application onfinely divided materials which have a tendency to adhere to rolls and on minerals of similar magnetic susceptibilitywhere clean cut separations of a series of magnetic products are desired. Results obtained with the laboratory model determine the application of the commercial unit to a particular problem. The main belt travels between the poles of two horseshoe magnets wherethe magnetic particles are attracted upward to cross belts which carry them to the side beyond the magnetic influence at which point they discharge. The intensities of the magnets may be varied by rheostat control and the gaps betweenmagnets and main belt are adjustable to requirements.
The Dings-Crockett (Wet Type) Submerged Belt Separator is designed for wet separation and is widely used in the concentration of magnetite and other strongly magnetic materials. It gives an amazingly clean cut separation of tailings, middlings and concentrates, effecting magnetic recoveries averaging over 99%. Standard accessory equipment consists of a wide range rheostat and corresponding ammeter for adjusting magnet field intensities.
The Dings-Davis Laboratory Magnetic Tube Tester Separator has been accepted as standard for determinations ofmagnetic content of ores and for checking efficiencies of wet separators. It is applicable to highly magnetic material such as magnetite, powdered iron, flue dust and ferro-silicon. The grade of concentrate that can be produced at any mesh size is quickly determined with this apparatus.
The tube tester consists of an electro-magnet, between the poles of which a glass tube is set at an angle of approximately 45. The tube is supported by an agitating mechanism which is agitated by a small universal electric motor. The tube is simultaneously rotated and agitated between the magnetic poles when the apparatus is in operation. Let our engineers make recommendations for the type and size magnetic separator units best suited to your problems.
The Stearns (Ring Type) Laboratory Magnetic Separator differs materially from the cross belt type; a steel take-off ring is employed in place of belts, to carry the magnetic material beyond the conveyor belt to final delivery. The laboratory unit is popular in many types of ore testing for treating small quantities of material for the recovery of feebly magnetic minerals. Standard accessories include rheostat, ammeter and switch, all mounted on a switch panel.
Prior to the extraction of the metal from the ore, it is necessary to separate, the ore from the gangue.This separation can often be achieved by physical means since mineral and gangue generally occur as separate solid phases.
This method of separation is used when either the ore particles or the gangue associated with it possess magnetic properties. For example, chromite Fe(CrO2)2 being magnetic can be separated from the non-magnetic silicious gangue by magnetic separation.
Collectors: These attach themselves by polar groups to grains of some mineral and form water repelling films on those minerals. Hence, these minerals attach with bubbles and go to froth. Collectors will attach with themselves only to minerals with definite chemical composition and lattice structure. They are high molecular weight organic compounds. The most common among them are xanthates, carboxylic acids and their salts.
Activators and Depressants:Minerals similar in chemical composition, such as sulphides of copper, lead and zinc exhibit an almost equal ability to absorb collectors; for this reason, when present in the same suspension, they will tend to froth together. For the purpose of selective floatation, this tendency may be controlled by supplementary reagents, known as depressors. Depressors are inorganic compounds, which form films on solid particles, thereby preventing the absorption by collectors. The film is produced through a chemical reaction between the depressor and the surface layer of the mineral.
The collector effect may be enhanced by activators. They are inorganic compounds soluble in water. Added to the suspension, an activator can destroy or modify the depressor film on the solid particles so that they are now able to absorb the collector ions or molecules and becomes floatable. For example, galena (PbS) is usually associated with zinc sulphide (ZnS), pyrites (FeS2) and quartz (SiO2).
Floatation is carried out by using potassium ethyl xanthate (Collector) along with sodium cyanide and zinc vitriol (depressants). They depresses the floatation property of ZnS grains by forming a complex, so mainly PbS passes into the froth when air is blown in. The froth spills over and is collected. After galena as been removed with the froth, the process is repeated by adding CuSO4(activator). This break the depressor film on ZnS grains hence, now these grains are available for collector, which are removed with the froth. The acidification of remaining slurry leads to the floatation of pyrites.
Question : How does NaCN act as a depressant in preventing ZnS from forming the froth? Solution: NaCN forms a layer of zinc complex, Na2[Zn(CN)4] on the surface of ZnS and thus prevents it from the formation of froth.
Leaching method is used for concentrating ores of aluminium, silver, gold etc. For example, bauxite (AI2O3.2H2O), is concentrated by this method. Crude bauxite contains ferric, oxide, titanium oxide and silica. These impurities are removed by making use of the amphoteric nature of alumina. Finely powdered bauxite is treated with an aqueous solution of caustic soda at 420-440 K under pressure for several hours. Alumina present in bauxite dissolves forming soluble sodium aluminate. AI2O3 + 6NaOH 2Na3AIO3 + 3H2O The impuritie remain unaffected and separate as insoluble red mud, which is filtered off. The filtrate is diluted and a little freshly precipitated aluminium hydroxide is added which causes the precipitation of aluminum hydroxide. This is filtered and calcinated to get highly pure alumina.Na3.AIO3 + 3H2O AI(OH3) + 3NaOH 2AI(OH)3 AI2O3 + 3H2O
Thickening: Prior to precipitation, it is sometimes advantageous to concentrate the solution. This is especially true to learn materials, the leached solution of which are usually diluted or contain large amount of impurities. This concentration is called thickening. It is accomplished by means of ion-exchange method.
Precipitation The metal sought or its compounds obtained by leaching are precipitated from the solution after it has been separated from the undissolved residue by means of filtering or settling. In elemental form, a metal can be precipitated from a solution either electrochemically, as in copper, zinc or nickel or by cementation according to reaction.
To read more,Buy study materials of General Principles & Isolation of Elementscomprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.
In nature, metals are not available in pure form. They are found contaminated with other elements in materials called ores. The unwanted material in an ore is called gangue. The process of removing the gangue from the ore to obtain the pure metal is called the concentration of ores. In this article, we look at the four major methods of concentration of ores.
In this process, the upward running water stream is used for washing the powdered ore. The gangue particle is washed off leaving heavier ore particles in it. It can be considered as a type of gravity separation.
It is used to remove gangue from sulfide ores. Suspension is created in water and ore is powdered and this collector and froth stabilizers are added. Collectors in this increase the non-wettability of the metal part of ore which allows it to form froth. And the froth stabilizers sustain the froth. Oil wets metal and water wet gangue. Paddles constantly stir up the suspension to form froth. And then this froth metal is skimmed off the top and dried for recovering the metal.
This process is used when the ore is soluble insolvent. The powdered ore is dissolved in a strong solution of NaOH, this chemical solution dissolves the metal in ore and is extracted and separated from the gangue by extraction of chemical solution. From bauxite ore, the extraction of aluminum metal is done using this process.
Ores are solid material from which a pure metal can be obtained. The process of removal of unwanted material from the ore is known as concentration or dressing or benefaction of ores. It involves several steps. The separation of required material from the ore is dependent on the differences in physical properties of the compound of the metal present and that of the gangue.
It is based on the difference in gravity of the particles of the gangue and the ore. So, it is considered as a type of gravity separation. During this process, an upward stream of running water is used to wash the powdered ore. The lighter gangue particles are washed leaving the heavier ore particles. Hydraulic washing is used for ores that have tin or lead, as they are heavier than the gangue.
It is based on the principle of magnetic properties of the ore components. If either the ore particles or the gangue are capable of being attracted in a magnetic field, magnetic separation can be used. Ore is kept in a conveyer which passes through the magnetic roller.
This method is used to separate gangue from the sulphide ores. This process is used for sulfide ores of Cu, Pb and Zn. Suspension of powdered ore is prepared using water. To this suspension, collectors and froth stabilizers are added. Pine oils, fatty acids are used as collectors to enhance the non-wettability of the mineral particles. Whereas froth stabilizers such as cresols, aniline, are added to stabilize the froth. A rotating paddle agitates the mixture and draws air in it. This results in the formation of froth which carries the mineral particles. The froth is light and is scanned off. It is then dried for recovery of the ore particles. Sometimes depressants are used to separate the sulphide ores by adjusting the proportion of oil to water. Such as, in case of an ore containing Zinc sulphide and lead sulphide. The depressant used is sodium cyanide.
Mineral processing, art of treating crude ores and mineral products in order to separate the valuable minerals from the waste rock, or gangue. It is the first process that most ores undergo after mining in order to provide a more concentrated material for the procedures of extractive metallurgy. The primary operations are comminution and concentration, but there are other important operations in a modern mineral processing plant, including sampling and analysis and dewatering. All these operations are discussed in this article.
Routine sampling and analysis of the raw material being processed are undertaken in order to acquire information necessary for the economic appraisal of ores and concentrates. In addition, modern plants have fully automatic control systems that conduct in-stream analysis of the material as it is being processed and make adjustments at any stage in order to produce the richest possible concentrate at the lowest possible operating cost.
Sampling is the removal from a given lot of material a portion that is representative of the whole yet of convenient size for analysis. It is done either by hand or by machine. Hand sampling is usually expensive, slow, and inaccurate, so that it is generally applied only where the material is not suitable for machine sampling (slimy ore, for example) or where machinery is either not available or too expensive to install.
Many different sampling devices are available, including shovels, pipe samplers, and automatic machine samplers. For these sampling machines to provide an accurate representation of the whole lot, the quantity of a single sample, the total number of samples, and the kind of samples taken are of decisive importance. A number of mathematical sampling models have been devised in order to arrive at the appropriate criteria for sampling.
After one or more samples are taken from an amount of ore passing through a material stream such as a conveyor belt, the samples are reduced to quantities suitable for further analysis. Analytical methods include chemical, mineralogical, and particle size.
Even before the 16th century, comprehensive schemes of assaying (measuring the value of) ores were known, using procedures that do not differ materially from those employed in modern times. Although conventional methods of chemical analysis are used today to detect and estimate quantities of elements in ores and minerals, they are slow and not sufficiently accurate, particularly at low concentrations, to be entirely suitable for process control. As a consequence, to achieve greater efficiency, sophisticated analytical instrumentation is being used to an increasing extent.
In emission spectroscopy, an electric discharge is established between a pair of electrodes, one of which is made of the material being analyzed. The electric discharge vaporizes a portion of the sample and excites the elements in the sample to emit characteristic spectra. Detection and measurement of the wavelengths and intensities of the emission spectra reveal the identities and concentrations of the elements in the sample.
In X-ray fluorescence spectroscopy, a sample bombarded with X rays gives off fluorescent X-radiation of wavelengths characteristic of its elements. The amount of emitted X-radiation is related to the concentration of individual elements in the sample. The sensitivity and precision of this method are poor for elements of low atomic number (i.e., few protons in the nucleus, such as boron and beryllium), but for slags, ores, sinters, and pellets where the majority of the elements are in the higher atomic number range, as in the case of gold and lead, the method has been generally suitable.
A successful separation of a valuable mineral from its ore can be determined by heavy-liquid testing, in which a single-sized fraction of a ground ore is suspended in a liquid of high specific gravity. Particles of less density than the liquid remain afloat, while denser particles sink. Several different fractions of particles with the same density (and, hence, similar composition) can be produced, and the valuable mineral components can then be determined by chemical analysis or by microscopic analysis of polished sections.
Coarsely ground minerals can be classified according to size by running them through special sieves or screens, for which various national and international standards have been accepted. One old standard (now obsolete) was the Tyler Series, in which wire screens were identified by mesh size, as measured in wires or openings per inch. Modern standards now classify sieves according to the size of the aperture, as measured in millimetres or micrometres (10-6 metre).
In order to separate the valuable components of an ore from the waste rock, the minerals must be liberated from their interlocked state physically by comminution. As a rule, comminution begins by crushing the ore to below a certain size and finishes by grinding it into powder, the ultimate fineness of which depends on the fineness of dissemination of the desired mineral.
In primitive times, crushers were small, hand-operated pestles and mortars, and grinding was done by millstones turned by men, horses, or waterpower. Today, these processes are carried out in mechanized crushers and mills. Whereas crushing is done mostly under dry conditions, grinding mills can be operated both dry and wet, with wet grinding being predominant.
Some ores occur in nature as mixtures of discrete mineral particles, such as gold in gravel beds and streams and diamonds in mines. These mixtures require little or no crushing, since the valuables are recoverable using other techniques (breaking up placer material in log washers, for instance). Most ores, however, are made up of hard, tough rock masses that must be crushed before the valuable minerals can be released.
In order to produce a crushed material suitable for use as mill feed (100 percent of the pieces must be less than 10 to 14 millimetres, or 0.4 to 0.6 inch, in diameter), crushing is done in stages. In the primary stage, the devices used are mostly jaw crushers with openings as wide as two metres. These crush the ore to less than 150 millimetres, which is a suitable size to serve as feed for the secondary crushing stage. In this stage, the ore is crushed in cone crushers to less than 10 to 15 millimetres. This material is the feed for the grinding mill.
In this process stage, the crushed material can be further disintegrated in a cylinder mill, which is a cylindrical container built to varying length-to-diameter ratios, mounted with the axis substantially horizontal, and partially filled with grinding bodies (e.g., flint stones, iron or steel balls) that are caused to tumble, under the influence of gravity, by revolving the container.
A special development is the autogenous or semiautogenous mill. Autogenous mills operate without grinding bodies; instead, the coarser part of the ore simply grinds itself and the smaller fractions. To semiautogenous mills (which have become widespread), 5 to 10 percent grinding bodies (usually metal spheres) are added.
Yet another development, combining the processes of crushing and grinding, is the roll crusher. This consists essentially of two cylinders that are mounted on horizontal shafts and driven in opposite directions. The cylinders are pressed together under high pressure, so that comminution takes place in the material bed between them.