Bulk collector

The amount of chemical mass removed from the atmosphere by rain and snow is more easily measured, by collecting and analyzing precipitation, than is the mass removed by dry deposition. Figure 4-33 shows an apparatus widely used to measure the deposition of atmospheric acids in North America. When a sensor detects the presence of precipitation, a motor moves the small roof away from the bucket, allowing rain or snow to collect in the wet bucket. If the movable roof is omitted, the collector is said to be a bulk collector. 

In addition, precipitation has been collected on a daily basis at two rural sites in Thailand since mid-1991 in rural locations (Granat et al, 1996). Samples were analyzed for conductivity, pH, NHa ", Na", K+, Mg +, Ca " ", SO, NO and CD. A high correlation was observed between H" " andSO suggesting that sulfur played an important role in acidification. Also, a strong interrelationship between Na+ and CD was found. The authors found a high correlation between NH4+ and NOj but the reason for this relationship was not obvious. Bulk collectors gave results 10-30% higher than wet-only collectors. 

The amount of sulfur found in stand precipitation is significantly greater than in bulk precipitation, because forests collect atmospheric sulfur much more efficiently than do bulk collectors. In contrary to sulfur, nitrogen fluxes to bulk collectors may exceed the fluxes in stand precipitation. This is due to the uptake of nitrogen by the canopy. 

Measurements may be made directly with the extracts from filters, bulk collectors, particle collectors, solution bubblers, or diffusion tubes, or following concentration on solid cartridges or guard columns. Usually, air is first passed through the collected material and is then extracted into solutions for analysis. 

If condensation requires gas stream cooling of more than 40—50°C, the rate of heat transfer may appreciably exceed the rate of mass transfer and a condensate fog may form. Fog seldom occurs in direct-contact condensers because of the close proximity of the bulk of the gas to the cold-Hquid droplets. When fog formation is unavoidable, it may be removed with a high efficiency mist collector designed for 0.5—5-p.m droplets. Collectors using Brownian diffusion are usually quite economical. If atmospheric condensation and a visible plume are to be avoided, the condenser must cool the gas sufftciendy to preclude further condensation in the atmosphere. 

A wide variety of special-purpose incinerators (qv) with accompanying gas scmbbers and soHd particle collectors have been developed and installed in various demilitarisation faciUties. These include flashing furnaces that remove all vestiges of explosive from metal parts to assure safety in handling deactivation furnaces, to render safe small arms and nonlethal chemical munitions fluidized-bed incinerators that bum slurries of ground up propellants or explosives in oil and rotary kilns to destroy explosive and contaminated waste and bulk explosive. 

Excess collector can also reduce the separation by forming micelles in the bulk which adsorb some of the colhgend, thus keeping it from the surface. This effect of the micelles on Ki for the colhgend is given theoretically [Lemhch, Principles of Foam Fractionation, in Periy (ed.). Progress in Separation and Purification, vol. 1, Interscience, New York, 1968, chap. 1] by Eq. (22-44) [Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972] if F, is constant when C, > C-... 

Bulk alum can be stored in mild steel or concrete bins with dust collector vents located in, above, or adjacent to the equipment room. Recommended storage capacity is about 30 days. Dry alum in bulk form can be transferred or metered by means of screw conveyors, pneumatic conveyors, or bucket elevators made of mild steel. Pneumatic conveyor elbows should have a reinforced backing as the alum can contain abrasive impurities. 

Ferric sulfate is usually stored in the dry state either in the shipping bags or in bulk in concrete or steel bins. Bulk storage bins should be as fight as possible to avoid moisture absorption, but dust collector vents are permissible and desirable. Hoppers on bulk storage bins should have a minimum slope of 36 however, a greater angle is preferred. 

Soda ash is usually stored in steel bins and where pneumatie-filling equipment is used, bins should be provided with dust collectors. Bulk and bagged soda ash tend to absorb aonospheric COj and water, forming the less aetive sodium bicarbonate (NaHCOj). Material reeommended for unloading facilities is steel. 

On the basis of the function it performs, the flotation process can be divided into two categories (i) bulk and (ii) selective. The process is called bulk or collective flotation when it accomplishes the separation of several valuable components from the gangue minerals. In selective flotation, one valuable component is separated from several others. This selectivity could be accomplished by either using collectors selective with respect to a particular mineral or by differential flotation wherein two or more mineral concentrates are recovered consecutively from the same feed by using modifiers. 

In accordance with this model, the current path is made through the contact resistance external collector - volume collectors (Rki), then goes through many other resistances, such as bulk resistance of the conductive particles (Rvi) and the contact resistance between the conductive particles in the volume of the electrode (Rci) at the end, there is contact resistance between the conductive particles and active mass particles (Rmi). 

The type of collector and flowsheet configuration play an important role in gold recovery from these ores. With a flowsheet that uses bulk Cu-Pb flotation followed by Cu-Pb separation, the gold recovery is higher than that achieved with a sequential Cu-Pb flotation flowsheet. In laboratory tests, and Aerophine collector type, in combination with xanthate, had a positive effect on gold recovery as compared to either dithiophosphate or thionocarbamate collectors. Table 17.10 compares the metallurgical results obtained with an Aerophine collector to those obtained with a dithiophosphate collector. 

Laboratory studies conducted on Falconbridge ores, also from the Sudbury Region, during 1980 [16] showed that PGM recovery can be improved with the use of a secondary collector. Figure 18.5 shows the effect of level of secondary collector on PGM recovery in a Cu-Ni bulk concentrate. The highest PGM recoveries were achieved using isobutyl dithiophosphate (Minerec 2087) as the secondary collector. 

Figure 18.5 Effect of secondary collectors on PGM recovery in a bulk Cu-Ni concentrate.

Throughout the development testwork, emphasis was placed on finding an effective reagent scheme that would produce a bulk concentrate with satisfactory tantalum, niobium and zircon recoveries. The Ta/Nb-Zr separation study concentrated mainly on magnetic separation. The floatability of Ta/Nb and Zr depend on type of collector, modifier and depressant system used. 

In order to achieve high bulk concentrate recoveries, relatively high additions of collector are required. 

The sulphosuccinamate collector was extremely effective in flotation of rutile, as well as ilmenite and zircon from a fine sand deposit. Laboratory testing conducted on Wimmera heavy mineral sand from Australia indicated that the use of sulphosuccinamate achieved a high titanium recovery in the bulk cleaner concentrate. Table 25.4 shows the results obtained on the Wimmera heavy mineral sand. The sand was scrubbed and deslimed before flotation. Between 90% and 95% Ti02 was recovered using a 60g/t addition of succina-mate collector. 

The bulk flotation can be accomplished with the addition of small doses of oleic acid plus oxidized emulsion of fuel oil. The fuel oil is treated with 10% solution of NaOH at a temperature of 60-80°C for 1 h. The following method was used for rutile-zircon separation the concentrate was thickened, followed by heat conditioning to 60°C. After the heat treatment, the zircon was floated without the addition of collector. The zirconium tailing is the rutile concentrate. The zircon concentrate was thickened, followed by gravity cleaning. In some cases, the heat-treated pulp is washed before zircon flotation. The following metallurgical results were obtained ... 

Method 3 - It involves bulk titanium/zircon flotation using succinamate collector followed by bulk concentrate pretreatment and selective zircon flotation. This method was developed for beneficiation of the Wimmera heavy mineral sand from Australia [12], The beneficiation flowsheet with type and level of reagents is shown in Figure 25.17. 

In these tests, the mixture of Na2Si03/tall oil was added to the scrubber before desliming. Collector used in the bulk circuit was sulphosuccinate. In the rutile circuit, phosphoric acid ester was used. Silica was rejected in a bulk talking. The overall metallurgical results obtained in the continuous operation are shown in Table 25.12. 

If minority carrier current (1BC, dotted line, symbols in Fig. 3.2) is detected at the collector, it can be concluded that the emitter is no sink for minorities. The absolute value of IEB depends not only on the charge state of the emitter-base junction and surface recombination velocity, but as well on bulk diffusion length and on sample thickness. However, the latter two parameters are constants for a given sample. 

This is the regime of cathodic currents. The silicon atoms of the electrode do not participate in the chemical reaction in this regime. An n-type electrode is under forward bias and the current is caused by majority carriers (electrons). The fact that photogenerated minority carriers (holes) are detectable at the collector indicates that the front is under flat band or accumulation. A decrease of IBC with cathodization time is observed. As Fig. 3.2 shows, the minority carrier current at the collector after switching to a cathodic potential is identical to that at VQcp in the first moment, but then it decreases within seconds to lower values, as indicated by arrows in Fig. 3.2. This can be interpreted as an increase of the surface recombination velocity with time under cathodic potential. It can be speculated that protons, which rapidly diffuse into the bulk of the electrode, are responsible for the change of the electronic properties of the surface layer [A17]. However, any other effect sufficient to produce a surface recombination velocity in excess of 100 cm s 1 would produce similar results. 

The schematic of the temperature sensor on the bulk chip is shown in Fig. 5.3. The bulk chip temperature is measured via the voltage difference between a pair of diode-connected pnp-transistors (parasitic transistors as available in the CMOS process, collectors tied to substrate) working at different current densities. Transistor Qi is biased with a current of 40 pA, and transistor Q2 is biased with a current of 10 pA. 

The one hundred year history of froth flotation may be classified into three periods. The earliest stage is from the end of the 19 century to the early 20 century, i.e. surface flotation or bulk oil flotation. The natural hydrophobic sulphide minerals can be collected by the addition of oil. Froth flotation came into practice in 1909 with the use of pine oil, mechanical flotation machine in 1912, and xanthate and aerofloat as collectors in 1924—1925 (Gaudin, 1932 Sutherland and Wark, 1955). 

Workers have shown theoretically that this effect can be caused both at the microstructural level (due to tunneling of the current near the TPB) as well as on a macroscopic level when the electrode is not perfectly electronically conductive and the current collector makes only intermittent contact. ° Fleig and Maier further showed that current constriction can have a distortional effect on the frequency response (impedance), which is sensitive to the relative importance of the surface vs bulk path. In particular, they showed that unlike the bulk electrolyte resistance, the constriction resistance can appear at frequencies overlapping the interfacial impedance. Thus, the effect can be hard to separate experimentally from interfacial electrochemical-kinetic resistances, particularly when one considers that many of the same microstructural parameters influencing the electrochemical kinetics (TPB area, contact area) also influence the current constriction. 

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