Leach water

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

AH stacks and vents attached to the process equipment must be protected to prevent environmental releases of hexavalent chromium. Electrostatic precipitators and baghouses are desirable on kiln and residue dryer stacks. Leaching operations should be hooded and stacks equipped with scmbbers (see Airpollution control methods). Recovered chromate values are returned to the leaching-water cycle. 

Although most of the volatile components are released to the atmosphere, a small fraction is dissolved and/or carried away with the water in the soil matiix. Leached waters are carried with the water as it percolates through the underlying soil strata. Most of the organic constituents contained in the leachate receive additional treatment as they pass through the soil cohimn. Leached wastes can also be lost in surface rtinoff. 

Stillings 1995). This dissolution generates an Al-Ca-poor thin layer at the surface, which is consistent with the lower Al-Ca release rates obtained in the leaching waters of the weathered waste rocks. The S release rates obtained from the fresh and weathered waste rocks are of the same order, suggesting that sulfide oxidation occurs at approximately the same rate in both, assuming that all the oxidation products do end up in the... 

The nitrate leaching rate can be described by the N-concentration in the leaching water and the amount of leakage water. Table 4-7 shows research results indicating nitrate leaching rates with respect to a per hectare and a per output unit scale. 

An example of the kinds of data required for land disposal options would be Information on soll/pestlclde Interactions to determine the effect of the pesticide on the soil and soil on the pesticide. The physical composition of the soil and the physical properties of the pesticide and Its formulation will determine the adsorption, leaching, water dispersal, and volatilization of the pesticide which. In turn, determine the mobility of the pesticide In soil. Even pesticides of closely related structures may have very different soil retention properties. Much of this data will be available from that developed to meet other registration data requirements with the exception that disposal rates are often orders of magnitude higher than normal application rates and the difference must be considered. 

Leaching with Airlift Recirculator. In a similar method (6) used by other investigators, 50 mL of distilled water at room temperature is recirculated over a sample at a rate of 250 mL/min by means of an airlift recirculator. The leach water is sampled and is changed periodically. 

A yellow color of the leach water is normal and results from a small fraction of strontium chromate which also forms. 

Jones, D.R., Chapman, B.M. and Jung, R.F. (1990) Column leaching of unretorted and retorted oil shales and claystone form the Rundle deposit water leaching. Water Research, 24(2), 131-41. 

A small portion of the product is tested for any unreacted platinum(IV) chloride by leaching with a few drops of hot water. An equal volume of a saturated solution of ammonium chloride is added to the leach water, and if there is no precipitate within 1 minute the product is pure. If a precipitate appears, the entire product should be leached with water until free of the soluble platinum(IY) chloride. The purified product is partially dried by suction filtration and finally completely dried by a drying agent in a desiccator. The yield is 2.8 g. (91% based on H2PtCl6-6H20). Anal. Calcd. for PtCl2 Pt, 73.3 Cl, 26.6. Found Pt, 73.0 Cl, 26.8. ... 

Yadav, J. S. P. and I. K. Girdhar. 1980. The effects of different magnesium calcium ratios and sodium adsorption ratio values of leaching water on the properties of calcareous versus noncalcareous soils. Soil Sci. 131 194-198. 

Yoh M. (2001) Soil C/N ratio as affected by climate an ecological factor of forest NO3 leaching. Water Air Soil Pollut. 130, 661-666. 

Evaporation of the leach water from 1000 g of phosphogypsum and X-ray diffraction of the resulting crystals did not identify any compounds of trace elements. Trace elements may exist as sulfates, such as mercuric sulfate, or as calcium salts, such as calcium selenate, in equilibrium with a saturated solution of calcium and sulfate ions from gypsum. Further isolation of trace elements by extraction, precipitation, ion exchange, or other means would so alter this equilibrium that the original amounts and types of compounds present would not be determined. Literature studies of phase equilibria in saturated gypsum solutions were used to identify possible trace element compounds. 

The second class of pesticide transport processes is that of movement of dissolved or particulate-sorbed pesticides in water. Leaching of pesticides hais been recognized as a critical process, if not in the sense of the absolute percentage of applied pesticide leached into the soil profile, then with respect to the contamination of groundwater by trace quantities of pesticide. Several pathways of dissolved pesticide movement with leaching water are recognized (18). 

The aims of reclamation are to make Ca2+ the major exchangeable ion and to reduce the salt concentration in the soil solution. The main requirement to reclaim salt-affected soils is that sufficient water must pass through the plant root zone to lower the salt concentration to acceptable values. Passing 1 m of leaching water per meter of soil depth under ponded conditions normally removes approximately 80% of the soluble salt from soils (Fig. 11.6). If leaching is under unsaturated conditions, such as with the use of intermittent pending or sprinkler irrigation, this quantity of water may be reduced to as little as 350 to 200 mm of water. Boron removal can require up to three times more water than removal of Na and Cl salts, because B is retained to some extent by soils. 

Cooke, R.A., Mostaghimi, S. Woeste, F. (1995). Effect of hydraulic conductivity probability distribution on simulated solute leaching. Water Environ. Res. 67, pp. 159-168. 

Figure 5. Main ion content of leaching water at different time.

It is often the case that solving one pollution problem tends to create another. This is very much so with the dusts and sludges produced in cleaning up gas streams, such as those from power plants. These materials may be undesirable and potential sources of pollutants such as heavy metals. Disposed in landfills, they may have a tendency to leach water pollutants into groundwater. 

Not only the containment problem was difficult with calcium polyphosphate melts, but leaching and fiber opening were also involved. Separation problems of leachate solubles were certain to be difficult engineering challenges. It would be necessary to recapture dissolved phosphate in leach water before it could be recycled. The cost of phosphate in leach water was too expensive to consider it as waste and recycling was to be expensive also. 

The formation of a primitive soil below lichens has several significant consequences. Nutrients, particularly P, S, Mg, Ca, and K, which are frequently essential to other plants that may replace lichens, are stored in an available or potentially available form (Syers, 1964 Jacks, 1965). The development of cation exchange capacity and the production of exchangeable cations, such as Ca, has been reported by Aidinyan (1949). The retention of cations and anions by the exchange complex should retard losses by leaching. Water-holding capacity should increase because of the accumulation of organomineral material and this may provide a more favorable habitat for the development of plants such as mosses. 

Aqueous leaching Water Several temp, and times 196,650,1121... 

---