In nature, soil particles such as clays, oxides, peat moss, and humus adsorb mercury from rainfall and remove it from the cycle. The tendency of mercury to sink rapidly and combine with sulfide in anaerobic bottom sediments to form cinnabar (HgS) appears to be a major scavenging mechanism. Reaction of mercury with organic matter is another such mechanism.
For industrial and metallurgical effluents, the removal treatment must fit the concentration of mercury and the quantity and composition of effluent. The following steps and principles apply for preliminary handling:
1. Isolate the mercury-bearing water from mercury-free effluent.
2. Minimize the use and quantity of water.
3. Recycle contaminated water. In order to accomplish this some simple treatment such as cooling, settling, or filtering may be necessary.
4. Use V-shaped rather than rectangular trenches or floor drains.
5. Use a series of traps to collect solids.
6. Impound wastewater in a tank or leak-proof pond for temporary storage and to even out the variations in flowrates and composition.
7. Observe that pumping underground may be possible in some cases.
8. Settle, filter, or both.
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