Concurrent leaching

Phosphate-induced metals stabilization can be used for the remediation of metals in mixed waste streams concurrently with other remediation technologies such as vapor stripping or bioremediation of organics. Using apatite to treat soils contaminated with lead, cadmium, and/or zinc can significantly reduce the amount of metals leached from the soil. The amount of apatite needed for treatment is less than 1% by weight. The reaction between metals and apatite is immediate, and the apatite can be heavily loaded with metals. 

For liquid or solid samples more complex than water, a combination of techniques is commonly required. Certainly a first step involves a need to obtain the components of interest in a solution phase. This may either involve leaching of a solid or extraction of a liquid sample with or without concurrent concentration. If the components of interest are then obtained in a water system, the techniques applicable to water analyses are immediately available. Conversely, if the extraction is into a non-miscible organic solvent and the components sought can be reextracted into water by appropriate choice of pH, then again the techniques of water sample processing can be used. 

Decomposition consists of three concurrent processes communition or fragmentation, leaching of water-soluble compounds, and microbial catabolism. Decomposition can also be viewed as a sequential process, what Eijsackers and Zehnder (1990) compare to a Russian matriochka doll. 

The net increase in dissolved-P release from land due to human activities also includes deforestation (plus concurrent soil loss), sewage, and waste sources (Fig. 4). Deforestation, typically by burning after selective tree harvesting, converts the standing stock of P in plant matter to ash. This P is rapidly leached from the ash and transported as dissolved loads in rivers this transfer can happen on timescales of a year or two (Schlesinger 1997). Furthermore, the lack of rooted stability on the landscape results in... 

All sulfur is shown to convert to sulfate ions in solution. Under the conditions of leaching, much of the sulflir remains in solution as metastable soluble intermediates. Oxidation of sulfur occurs in the sequence thiosulfate ions, 203 thionate ions, S 0 sulfamate ions, SO3NH3 and sulfate ions. SOl. The partially oxidized sulfur ions in solution must be converted to sulfate ions prior to nickel reduction to maintain nickel purity. One of the important features of the pressure-leaching process is the concurrent... 

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