Pachuca

The leaching is 50—60°C without external heating. The cone-bottom tanks are equipped with a pipe from just above the solution level to near the bottom through which air is blown forming bubbles which lower the density of the slurry. These leach tanks, caHed Pachucas, are fairly efficient and are stiH popular although many plants employ mechanical agitators. Most plants use 3—5 tanks in series with acid and calcine being fed to the first and, in some cases, downstream from the first tank as weH. 

The Dorr agitator (Coulson and Richardson, loc. cit.) consolidates in one unit the principles of the thickener and the Pachuca tank. Resembling a rake-equipped thickener, it differs in that the rake is driven by a hollow shaft through which the solids-liquid suspension is lifted and circulated by an air stream. The rake moves the pulp to the center, where it can be entrained by the air stream. The unit may be operated batchwise or continuously. 

Pachuca tank The simplest and most inexpensive device for agitating the pulp. Agitation is achieved by the injection of air under pressure into the bottom of a tall tank. The rising gas draws the surrounding liquid with it to the surface... 

The soil was collected from the Mezquital Valley, located near Pachuca in the State of Hidalgo (Mexico). The irrigation water used was slightly alkaline with a pH of 8.4. The experiment was carried out under greenhouse conditions. Soil collected from three sub sites was placed into cylindrical pots. Five treatments were established in order to study the effect of wastewater and urea on the cultivation of maize (Zen mays L.). The treatments were a) SMWW, maize plant plus wastewater b) SMUREA, maize plant plus urea as fertilizer c) SUREA, uncultivated soil and urea as fertilizer d) SWW, uncultivated soil plus wastewater and e) SCONTROL treatment, soil plus tap water. Soils from the SMWW and SWW treatments were irrigated with 1000 mL of wastewater every 7 days from the first day onwards, making a total of 13 times overall. This means that a total amount of mineral N equivalent to 120 kg N ha-1 was added to each maize plant, i.e. the recommended amount of N fertilizer for maize. 

An example of an agitated vessel in which compressed air is used is the Pachuca tank, shown in Figure 10.8. This is a cylindrical tank with a conical bottom, fitted with a central pipe connected to an air supply. Continuous circulation is obtained with the central pipe acting as an air lift. Additional air jets are provided in the conical portion of the base and are used for dislodging any material which settles out. 

The Mexican method referred to by Father de Acosta and Baron von Humboldt was the cold amalgamation, or patio, process introduced at Pachuca by Bartolome de Medina about the middle of the sixteenth century. As early as March 4, 1552, the governing princess (Princesa Gobemadora) in Valladolid acknowledged an urgent request for mercury to be used in the exploitation of silver (28). In this process, salt, mercury,... 

Figure 3. Regional map showing locations of Guatemalan (l=San Martin Jilotepeque 2=El Chayal 3=Ixtepeque) and Mexican (4=Pachuca 5=Zaragoza) obsidian sources used in the study.

Source determination of all 70 Postclassic obsidian samples was possible using the field-portable XRF instrument. Although the majority of the samples (56%, n=39) represent the Ixtepeque source, 29% (n=20) of the sample comes from El Chayal, and 11% (n=8) can be sourced to San Martin Jilotepeque. In addition to these Guatemalan sources, two different Mexican sources were identified in the Postclassic sample Pachuca (3%, n=2) and Zaragoza (1%, n=l) (Figure 4). 

The pulp-water systems encountered in the agitation of paper stock represent a highly specialized case of solid-liquid agitation, discussed in a few papers (CIO, K5, 04), which will not be reviewed here. Lamont (L2) discusses the operation of pachuca tanks, used for ore-leaching operations, in which agitation results from air introduced at the tank bottom. 

The selective leaching of the nickel and cobalt from the gangue material is carried out in Pachuca-type leaching vessels with 98% sulfuric acid at temperatures between 450 and 500°F and with equivalent pressures between 400 and 600 psi. A typical leach liquor contains 6 gm/liter Ni, 0.6 gm/liter Co, 0.6 gm/liter Fe, 2.3 gm/liter Al, and 67 gm/liter SO4. Each batch is leached for about 90 min to extract 95% of the metal values. Preheating and heating of the ore slurry is by direct steam absorption in the reaction vessel. The barren residue is separated from the leach liquor by countercurrent decantation to a density of 55-60% solids. The solids are washed with very little dilution and about 99.5% of the soluble value are recovered. 

The air-life fermentor consists of two concentric columns. The outer column has a conical bottom section with a perforated plate acting as a gas distributor. The inner column is positioned over this plate. Compressed air, enriched with CO2, is used to lift a suspension of mineral and bacterial culture in medium through this inner column. The suspension then falls to the reservoir and is air-lifted up the column again. The air-lift fermentor provides a good supply of oxygen and is able to keep high pulp densities (25%) of ore fully suspended in the medium. An illustrative example is provided by the work of Helle and Onken (47). Pachucas operate in a similar fashion to the air-lift fermentor, but there is no inner column. Air enters at the conical base of the reactor, aerates the medium, and suspends and circulates the mineral particles. Pachucas are useful reactors for building up culture stocks. 

Typically, this additional biological step is carried out in a pachuca, a cone-bottomed column familiar to the mining industry. Ground or milled ore, mixed with the aqueous bacterial solution, is introduced into the top of the column, and air is injected at the base. The injected air serves a number of functions it maintains the solid in suspension, it mixes the solid with liquid— giving a three-phase gas/liquid/ solid system—and it provides the oxygen and carbon dioxide required by the bacteria. The bacteria also require a feed of nitrogen and phosphorous, which can be added to the colunm if they are not indigenous to the ore. 

Pachuca.—This type of agitator, similar to the Dorr in. what it attempts to accomplish, has in recent years been almost completely replaced by other types. It consists of a very high tank with a conical bottom. Reaching from the top of the tank to the center of this cone is a pipe to be used as an air lift as in the Dorr, the idea being that as the particles sink they strike this conical bottom and slide... 

Pachuca Tanks Air-agitated Pachuca tanks were widely used in mineral processing until the 1960s when the industry concluded that mechanical agitation was more economical and more effective for solids suspension. A description of Pachuca tanks can be found in previous editions of Perry s Handbook. 

Knowing the type of rock also places strong constraints upon the geographic source of the material. Obsidian can be found, for example, only in young volcanic fields and in nearby deposits derived from them. Many can further visually identify stone materials from specific sources such as the green Pachuca obsidian found at sites in the Valley of Mexico or Hixton quartzite from west central Wisconsin, found at sites in the upper Midwestern USA. However, for most stone materials, distinction of the source of the raw material requires more sophisticated laboratory analyses. 

Centro de Investigaciones Quimicas, Universidad Autonoma del Estado de Hidalgo, Pachuca, Estado de Hidalgo, 42184, Mexico. 

If fouling is a problem, consider flash growth type Pachuca, draft tube MSMPR units, or classified product removal CPR type Oslo, krystall type. 

Immersion leach low solute leach rate. Product of residence time x concentration of leachant for acid leach = constant for a given particles diameter. Tends to have a separate leacher followed by system to separate and wash sohds. Pachuca plus CCD, settler particle diameter <70 pm sohds 30 to 60% w/w agitator 0.07 to 0.2 kW/m for CCD 1.5 to 2 kg liquid solvent carryover/kg inert solid. Autoclaves plus CCD particle diameter <70 pm solids 30 to 60% w/w 0.7 to 1.3 kW/m. ... 

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