Shaft Flotation

Wang, L.K. Preliminary Design Report of a 10-MGD Deep Shaft-Flotation Plant for the City of Bangor, PB88-200597/AS U.S. Department of Commerce, National Technical Information Service Springfield, VA, 1987 42 p. 

A simple separator used to recover the magnetic particles consists of a series of disks mounted on a shaft. Each disk has a number of permanent magnets mounted flush with the surface at its perimeter. The disks rotate into and out of the Hquid containing the suspended magnetic material and lift the magnetic particles out of the stream. The magnets are then scraped clean (Eig. 10). Very low residence times are needed for removal of the particles compared to settling or flotation (142). 

The aeration requirements of the deep shaft (vertical shaft bioreactor using flotation technology) are provided by two, 100 hp rotary screw compressors rated at a pressure of 7 kg/m2 (100 psig). Dissolved oxygen (DO) levels of 4 mg/L are maintained in the head tank, and during the startup phase of the plant a DO meter measured a dissolved oxygen concentration of 25 mg/L at the shaft bottom. 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

Mechanical Cells. Figure 19-73 presents a schematic representation of a typical mechanical device commonly known as a flotation cell. It is characterized by a cubic or cylindrical shape, equipped with an impeller surrounded by baffles with provisions for introduction of the feed slurry and removal of froth overflow and tailings underflow. The machines receive the supply of air through a concentric pipe surrounding the impeller shaft, either by self-aeration due to the pressure drop created by the rotating impeller or by air injection by means of an external blower. In a typical installation, a number of flotation cells are connected in series such that each cell outputs froth into a launder and the underflow from one cell goes to the next one. The cell design may be such that the flow of slurry from one cell to another can either be restricted by weirs or unrestricted. 

In the chief class of flotation machines the air is actually beaten into the oiled froth by revolving beater or impellers. Beaters mounted on horizontal shafts have received much attention from inventors in recent years. They revolve at lower speeds than the machines using vertical impellers and are arranged to trap the air by having the 22... 

Chamber dryers equipped with stirrers are commonly nsed for drying of flotation concentrates (Figure 51.4). The dryer operates in a cocurrent mode. Hot combustion gases supplied to the dryer by a duct (5) meet at the outlet the cold and moist coal supplied by another duct (7). The dryer consists of a chamber (1) fitted with baffles (9) and two shafts (2) rotating... 

One piece or one set of optional shim is located between the input shaft flange and center of stator support shaft axle of and used to control the end flotation of transmission. The structure arrangement allows the inspection for the subassembly during the product manufacturing period. 

The flotation experiments, which have been analysed, were all carried out using Denver flotation equipment. The cell has approximately Idm capacity and 600 g of slurry was used in every test. The dimensions of the cell are shown in Figure 3. The cell was located in the base of the frame, directly below the impeller shaft. Experimental details of the flotation tests are summarised in Table 1. 

Mineral flotation is a three phase process where solid phase consists of mineral grains, liquid phase is mainly based on water and air as gaseos phase. In Outokumpu flotation cells air is conducted through hollow shaft to the rotating rotors direct influence. Intense eddy currents throw bubbles and pulp against the stator blades and through the gaps of the vertical blades and are distributed evenly to the flotation cell. Hydrofobic minerals attached to bubbles are lifted up to the froth area and to the concentrate duct... 

The ore is crushed and ground and separated into various mineral concentrates by flotation. The complex lead-zinc ores have played an important role in the development of the flotation technique. A lead concentrate with perhaps 77% Pb is roasted to oxide, in general on a sinter band, a process in which sulfur is removed as sulfur dioxide. Limestone is added for slag formation and the sinter is reduced by coke in a shaft furnace. An alternative method is to use a rotating converter furnace, from which the sulfur dioxide can be used for sulfuric acid production. This is good for the environment and good for the economics of the process. 

We have studied the possibility of using ozone for improvement Ag extraction form polymers deposits in a flotation plant in the town of Rudo-zem. It has been found that upon blowing of ozone (1% vol concentration, flow rate - 3001/h) through the empty shaft of the flotation machine stirrer (5 m volume) the degree of Ag extraction is increased by 1-2% [139], The redox leaching of precious metals from manganese-containing ores carried out by other authors show also positive results [140],... 

Spodumene had been produced from the Preissac-Lacorne deposit by the Quebec Lithium Corp. from 1955 to 1959, supplying ore to LCA s North Carolina plant. Mining was conducted underground, with the initial area developed about 450 m in diameter from a 171 m deep shaft. After mining, the ore was concentrated by flotation (Kesler, 1960) in a mill near the shaft site with a capacity of 2000 mt/day of concentrates. This operation closed when LCA opened their own mine in North Carolina (Kunasz, 1994). 

The mechanical complexity makes mechanical induced flotation units the most maintenance-intensive of all gas flotation configurations. As a result of the need for motor shaft seals on penetrations to the cell, mechanical induced flotation units have traditionally operated very near atmospheric pressure. 

Many induced flotation units, particularly mechanical flotation units, operate at pressures within a few ounces of atmospheric pressure. The walls are thin and have numerous penetrations for motor shafts and observation hatches. As a result of the simplicity of design, air can easily enter the units around the paddle or if observation hatches are left open. Oxygen in the water treating system increases the corrosion rate in the unit as well as all downstream carbon steel equipment and can cause the formation of a reddish precipitate resulting from oxidation of dissolved iron in the treated water. To avoid corrosion and the precipitate, care should be taken to avoid oxygen ingress. Hatches should be left closed as much as possible, and the integrity of shaft seals should be maintained. 

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