Settling rate , precipitate

Trace metals are introduced to the ocean by atmospheric feUout, river runoff, and hydrothermal activity. The latter two are sources of soluble metals, which are primarily reduced species. Upon introduction into seawater, these metals react with O2 and are converted to insoluble oxides. Some of these precipitates settle to the seafloor to become part of the sediments others adsorb onto surfaces of sinking and sedimentary particles to form crusts, nodules, and thin coatings. Since reaction rates are slow, the metals can be transported considerable distances before becoming part of the sediments. In the case of the metals carried into the ocean by river runoff, a significant fraction is deposited on the outer continental shelf and slope. Hydrothermal emissions constitute most of the somce of the metals in the hydrogenous precipitates that form in the open ocean. 

These precipitators may increase the settling rate of water by a factor of 5. For example, settling droplets of sulfuric acid out of alkylate (a light hydrocarbon) by gravity alone might take an hour. A good electric precipitator can do a better job in just 10 min. Precipitators do not really consume much electricity. It is true that the electricity is applied... 

Digestion and Settling Rates of the Precipitate. To design the proper short leg-suction-jet, it was necessary to know the volume of slurry to be expected in the tank, rate of settling, and the minimum distance above the slurry that the jet must be to prevent movement of the slurry. 

The volume of precipitate and settling rate were determined by precipiration of 4 L of simulated NaN03 solution preadjusted to 1M HNO3 by the addition of 2 L of 0.9M The settling rate... 

Figure 6. Settling rate of typical simulated oxalate precipitate...

The volume of precipitate and settling rate were also determined by precipitation of 2 L of simulated solution, adjusted to 0.5M Al3+ and 0.25M HNO3 by the addition of 4 L of 0.9M H2C2O1. When the precipitation was carried out at room temperature, less than 10% of the precipitate had settled after a 60-hour settling period. When the oxalic acid was added to a 60°C solution and then held at 40-45°C for an additional 2 hours, the settling rate and final volume of precipitate were very similar to the Am-Cm material containing NaN03-... 

After irradiation the sample was dissolved in hydrochloric acid. A known amount of all the lanthanides (0.5-1 mg. each) and 10 mg. of barium were added, the cerium was oxidized and subsequently reduced to ensure complete exchange of carrier and cerium activity, and the lanthanides were separated and purified as a group using a series of fiuoride and hydroxide precipitations. The final hydroxide precipitate was dissolved in dilute hydrochloric acid and adsorbed to 80 mg. of Dowex 50. The resin was transferred to the top of an ion exchange column (Dowex 50X12, NH4 -form, settling rate 0.5-1.5 cm./min.), and the lanthanides were eluted using a-hydroxy-isobutyric acid and continu-... 

The first step in brine purification is chemical treatment to remove certain impurities. The elements of hardness (calcium and magnesium) must be removed, along with iron and heavy metals. This is done by precipitation, adding a source of carbonate ion to remove calcium and a source of hydroxide ion to remove the other metals. Sulfate ion also can be removed by precipitation, using either calcium or barium ion. Precipitation processes cannot usefully be considered in isolation. The nature of the solids formed in this way determines how they will behave in the later processes that are designed for their physical removal. The subsections that follow therefore describe in a general way the flow behavior and settling rates of precipitated particles. Later sections of the chapter cover the details of sedimentation and filtration of the solids. 

FIGURE 7.39. Effect of temperature on reaction/settling rate in calcium precipitation. 

Upgrading of the treatment was based upon both previous experience and bench-scale tests. The new plant would effect precipitation in a six tank cascade system, using a 4% lime slurry to raise the pH from 4 to 8.5-8.7 (Fig. 6.8). Floc-culants and conditioners would then be added and the effluent passed to a thickener tank. From here the effluent would pass at up to 120 m h" to a retention tank where the pH would be raised to pH 11-12, before final settling in a reactivator. Detailed tests showed that the precipitated lead was colloidal in character and hence difficult to settle. Addition and subsequent precipitation of iron improved the settling rate, but iron addition was not planned for the upgraded treatment plant. 

As also shown in Equation (4), Ni content in anode had much influence on Au content in cathode. It was mainly because solution viscosity increased due to Ni contained in electrolyte and settling rate of anode slime dropped, so fine particles of anode slime mechanically adhered to cathode, and Au content in cathode increased because of lump growth on cathode caused by worsen precipitation. 

Fio. 4-11. Effect of firing temperature on high-temperature settling rates. 250 g Th/kg H2O particle size 1 micron prepared from lO C precipitated oxalate. 

The capacity of any specific tank configuration, in terms of metric ton equivalents, is deterrnined by one of three parameters. (/) The solubiHty of waste salts. Precipitates can settle and cause thermal hot spots, which in turn can result in accelerated corrosion rates. Thus it is important to maintain the... 

N2, and traces of PH, CO2, E, and S large furnaces generate off-gas at a rate of about 120—180 m /min. In most installations the off-gas is passed through a series of Cottrell electrostatic precipitators which remove 80—95% of the dust particles. The precipitators ate operated at temperatures above the 180°C dew point of the phosphoms. The collected dust is either handled as a water slurry or treated dry. Einal disposal is to a landfill or the dust is partially recycled back to the process. The phosphoms is typically condensed in closed spray towers that maintain spray water temperatures between 20 and 60°C. The condensed product along with the accompanying spray water is processed in sumps where the water is separated and recycled to the spray condenser, and the phosphoms and impurities ate settled for subsequent purification. 

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