Separation and Concentration Methods

Mineral Specific gravity Hardness (Mohs Scale) 

The development of flotation separation methods was originally for the purpose of separating zinc minerals from mixed lead-zinc ores and initially from gravity separation tailings. Once this great breakthrough was achieved, attention was turned to the separation and concentration of lead minerals and thereafter flotation became the primary method of concentrating sulfide ores. 

size rednction of the ore so that the individual mineral grains are liberated and separated from one another, and 

selective physiochemical separation of the individual mineral grains by froth flotation to form separate metal concentrates. 

Primary crushing may reduce as mined ore to less than 200 mm and then, in the conventional approach, it is further reduced in secondary and tertiary crushers followed by rod and ball mill grinding to the required particle size. Final sizing classification is usually achieved by operating the ball mill in closed circuit with hydrocyclones. 

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This chapter includes sections on The Analytical Method, Sampling and Sample Treatment, Separation and Concentration, Method Classification, and Determinative Methods. The principal thrust of this chapter is a general summary of some of the more common and current analytical methodologies employed for the determination of total elemental contents in a wide variety of biological and environmental materials. Coverage here is general the reader is referred to other chapters in this book for particular details on individual elements covered there and to the many publications referred in this chapter. The chapter... 

Study of membrane extraction processes is a matter of primary importance for intensive development of separation and concentration methods of different nature substrates, especially such valuable ones as rare and scattered metals. The imique properties of rare earth metals (REM) allow using them in different realms of modem science and technology when making selective catalysts, magnets (samarium and neodymium), optical systems, luminophors, and ceramic capacitors. REMs are used in metallurgy for production of special cast iron grades, steel, and nonferrous metals alloys. REM additives increase quality of metallurgical products improve their properties, particularly shock resistance, viscosity, and corrosion resistance. Such materials are used primarily in aerospace industry. Extraction of REM from minerals is a complex process. 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

The same analytical methods as for liquid sodium have been applied. Distillation separates and concentrates the impurities prior to analysis. Amalgamation has poor recovery value for oxygen compared to distillation (Table 1). ... 

The concentration of organic materials in seawater is too low to merit direct utilization of many of the modern analytical instruments concentration by a factor of a hundred or more is necessary in many instances. Furthermore, the water and inorganic salts interfere with many of the analytical procedures. Separation of the organic components from seawater therefore accomplishes two purposes it removes interfering substances, and at the same time concentrates enough organic matter to make analysis possible. It is not surprising that considerable effort has been put into methods of separation and concentration. 

There is an extensive literature on concentration, separation, and fractionation methods. References [1-5] give general reviews. 

Using the newer methods, such as gas chromatography, liquid-liquid chromatography, fluorometry, and mass spectrometry, it is possible to measure many compounds at the parts-per-billion level, and a few selected compounds with special characteristics at the parts-per-trillion level. Even with these sensitivities, however, a considerable concentration must usually be undertaken to permit the chemical or physical fractionation necessary to render the final analyses interpretable. A major effort has therefore been expended on the study of methods of separation and concentration, and this is discussed further in Chap. 8. 

The anthocyanin profile of the flowers of Vanda (Orchidaceae) was investigated with a similar technique. Flowers (2 kg) were extracted with 101 of methanol-acetic acid-water (9 l 10,v/v) at ambient temperature for 24 h. The extract was purified by column chromatography, paper chromatography, TLC and preparative RP-HPLC. Analytical HPLC was carried out in an ODS column (250 X 4.6 mm, i.d.) at 40°C. Gradient conditions were from 40 per cent to 85 per cent B in 30 min (solvent A 1.5 per cent H3P04 in water solvent B 1.5 per cent H3P04, 20 per cent acetic acid and 25 per cent ACN in water). The flow rate was 1 ml/min and analytes were detected at 530 nm. The chemical structures of acylated anthocyanins present in the flowers are compiled in Table 2.90. The relative concentrations of anthocyanins in the flower extracts are listed in Table 2.91. It can be concluded from the results that the complex separation and identification methods (TLC, HPLC, UV-vis and II NMR spectroscopy, FAB-MS) allow the separation, quantitative determination and identification of anthocyanins in orchid flowers [262],... 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

With analytical methods such as x-ray fluorescence (XRF), proton-induced x-ray emission (PIXE), and instrumental neutron activation analysis (INAA), many metals can be simultaneously analyzed without destroying the sample matrix. Of these, XRF and PEXE have good sensitivity and are frequently used to analyze nickel in environmental samples containing low levels of nickel such as rain, snow, and air (Hansson et al. 1988 Landsberger et al. 1983 Schroeder et al. 1987 Wiersema et al. 1984). The Texas Air Control Board, which uses XRF in its network of air monitors, reported a mean minimum detectable value of 6 ng nickel/m (Wiersema et al. 1984). A detection limit of 30 ng/L was obtained using PIXE with a nonselective preconcentration step (Hansson et al. 1988). In these techniques, the sample (e.g., air particulates collected on a filter) is irradiated with a source of x-ray photons or protons. The excited atoms emit their own characteristic energy spectrum, which is detected with an x-ray detector and multichannel analyzer. INAA and neutron activation analysis (NAA) with prior nickel separation and concentration have poor sensitivity and are rarely used (Schroeder et al. 1987 Stoeppler 1984). 

Diazinon can be measured in air after pre-concentration from air onto some adsorbent material with subsequent extraction. Following extraction from the adsorbent, separation and detection methods include GC/MS (Hsu et al. 1988 Kuwata and Yasuhara 1994), GC/NPD (Williams et al. 1987), and GC/FPD in the P mode (NIOSH 1994). The method of Williams et al. (1987) applicable to both diazinon and diazoxon. The NIOSH method (Method 5600, NIOSH 1994) has been fully validated for use in occupational settings where regulatory exposure limits are of concern. 

The most common method for the separation and concentration of flavor chemicals before chromatography is solvent extraction. If the aroma active components in a sample are less than a microgram/liter then solvent extraction followed by fractional distillation can be used to concentrate the analytes above 1 4g/liter. This is done for two reasons (1) to remove the odorants from some of the interfering substances and nonvolatiles, and (2) to concentrate the sample for greater sensitivity. The choice of solvent(s) depends on a number of issues, but similar results can be obtained with many solvents. Table Gl.1.2 lists a number of solvents, their polarity, and physical properties. Pentane is the least polar and ethyl acetate the most. The sample must be an aqueous or dilute sample, dissolved or slurried into water to a final concentration of 80% to 90% water. Dilute aqueous samples will present the greatest polarity difference between the solvent and the sample, driving more volatiles into the extracting solvent. 

The solubilisation of proteins and amino acids in organic solvents by reversed micelles provides a new method for the selective recovery, separation and concentration of bioproducts using liquid->liquid extraction techniques. Selectivity is affected by electrostatic interactions between the charged residues or moieties of the solute and the surfactant headgroups. These interactions are mediated by electrostatic screening as affected by solution ionic strength. The more hydrophobic the amino acid residue, the more favourable is the solubilisation of this residue in the partially structured water pool of the reversed micelle relative to the bulk, unstructured water phase. 

The infrared identification method presented here is a selected combination of available methods for sample extraction, removal of interferences, separation and concentration of insecticides, and infrared spectrometry of micro samples. The method was developed using fish exposed in the laboratory to a variety of known pesticides it was applied successfully to fish samples collected at the site of a large fish kill. The procedure consists of the following steps ... 

The isolation and concentration of petroleum products can be performed in several ways. The most efficient method is passive adsorption. In this method, the sample along with a tube filled with Tenax TA adsorbent is placed in a thermostated (60-70 °C) tightly closed container, such as a glass jar, for over 10 h. Under these conditions, a balance between compounds present in the headspace of the sample and the sample adsorbed on the polymer adsorbent is established. Adsorbed compounds are subjected to thermodesorbtion then, the desorbed compounds together with the carrier gas are injected onto a GC column, where they are separated and then identified. This approach has enabled easy detection and identification of trace amounts of petroleum products. Headspace analysis with passive adsorption on Tenax TA is normally used for separation and concentration of analytes. Gas chromatography coupled with an autothermal desorber and a mass spectrometer (ATD-GC-MS) is the best technique for separation of multicomponent mixtures... 

There are many methods of separating and concentrating the elements in a given solution as exemplified by the techniques used in analytical chemistry. Oxidation, hydrolysis, and precipitation are among the techniques used in large-scale operation. 

The metal values associated with other minerals but not amenable to separation and concentration by the standard beneficiation techniques such as flotation can usually be recovered by chemical methods. The Climax Molybdenum process to recover the molybdenum oxide values associated with the sulfide ore and the Union Carbide process for the separation of molybdenum from tungsten in a floatation concentrate are in this category. 

The velocity and concentration profiles are developed along the HFs by means of the mass conservation equation and the associated boundary conditions for the solute in the inner fluid. This analysis separates the effects of the operation variables, such as hydrodynamic conditions and the geometry of the system, from the mass transfer properties of the system, described by diffusion coefficients in the aqueous and organic phases and by membrane permeability. The solution of such equations usually involves numerical methods. Different applications can be found in the literature, for example, separation and concentration of phenol, Cr(VI), etc. [48-51]. 

The experimental results in Figure 39.9 revealed that when the flow rate of the aqueous phase is higher than that of the organic phase in a hydrophobic membrane and with feed in 4 M HNO3 and 20% TBP as an extractant, the transport of uranium across the membrane is fast. Therefore, a HF contactor in strip dispersion mode with 20% TBP in nph as an extractant could be successfully used for the separation and concentration of U(VI) from nitric acid media. The feasibihty of this technique for the separation of U(VI) from dilute solutions using 0.01 M HNO3 solution as strippant even in the presence of fission products from waste streams makes it a viable alternative to conventional methods. 

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