Solubilities ground-water leaching

Data from in-situ leach mining and restoration of roll-front uranium deposits also provide information on the potential mobility of the waste if oxidizing ground water should enter the repository. Uranium solids probably will be initially very soluble in carbonate ground water however, as reducing conditions are re-established through water/rock interactions, the uranium will reprecipitate and the amount of uranium in solution will again equilibrate with the reduced uranium minerals ... 

A high log (Kow) means that the substance dissolves better in octanol than in water (e.g., if log Kow = 6, a million times). In practical terms this means that there is a risk that the substance accumulates in fat. On the other hand, a log (Kow) < -2 shows that the substance is a hundred times more soluble in water than in octanol. This usually is a warning sign that the substance has a tendency to leach into ground water. 

Selenium enters the food chain mainly as selenomethionine from plants that take the element up from the soil but do not appear to use it. The soil content of selenium is highly variable and can be low in volcanic soils when soluble salts are leached out by ground water. Soils in parts of China and New Zealand are particularly low in selenium. Acid soils, where insoluble selenium complexes can be formed with iron and aluminum, occur in some parts of Europe, resulting in low available soil selenium. The geographical source of plant and animal foodstuffs determines the level of dietary intake. In the United States and Canada, wheat and other cereal products are a good source of selenium average intakes in North America range from 80 to 220 fig Se per day, whereas in the UK dietary intake is about 30 to 60 Llg/day. Intakes in China are as low as 11 lg/day and in New Zealand 28 fig/day. ... 

Maneb or Mancozeb. Few data on the transport and partitioning of these maneb and mancozeb were located. Calumpang et al. (1993) reported a half-life of 2.9 days for mancozeb determined in a silty clay loam soil placed in experimental columns and maintained under field conditions. In other studies, the half-life for maneb in soil was estimated to be 3 weeks and 4-8 weeks (Nash and Beall 1980 Rhodes 1977). Using chemical and physical properties. Beach et al. (1995) estimated that the half-life in soils for maneb and mancozeb to 70 days. The high value estimated for these compounds (>2000) suggested to these authors that the potential for leaching into ground water would be low. However, the potential for solubility in surface water was considered to be moderate, despite the relatively low solubility of maneb and reportedly insolubility of mancozeb. 

At the completion of remediation, the processed volume of soil will have been acidified and natural re-equilibration may be possible. Alternatively, the area can be treated with acceptable alkalis such as lime or ammonia. The system total acidity is determined best with an acid-base titration. If alternative reactions are chosen at the electrodes to the production of acid and base, the effects of these on the whole system need to be evaluated in terms of the toxicity of electrode reactants and products, their influence on the soil/contaminant ion-exchange efficiency, the effectiveness of electroosmostic flushing, solubilities, etc. Leach tests can be used to assess if the residual contaminant achieves a level acceptable for ground water quality. 

Though a small percentage (0.3%) of the lead consumed is used in electronic assemblies, it could be better recycled. There is very little probability that lead can be leached from landfill into ground water because lead salts are not soluble in water. However, if electronic products are simply shredded and then incinerated, the lead dust from shredding or the ash from the incinerator will be finely divided and more available for environmental contamination. 

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