Several years ago the river Tisza (Hungary) was heavily contaminated with cyanides by a Romanian gold mine. What is your opinion, what should do in similar cases - to try to do something to treat contamination (with chemicals even with causing a less harmful secondary contamination but capture the cyanides) - or leave the primary contamination along the river to kill completely fish and other living animals ?
The answer depends on concentration of cyanide in water. Usually, in case of peroral accidental poisoning, it is possible to reduce the content of cyanide in a stomak drinking dilluted H2O2. Peroxide, or other oxidation agents /persulphate, Ca/ClO/2 / oxidize H-CN thus resulting HO-CN, that is by several orders less toxic compound than cyanides.The reaction of H2O2 with NaCN proceeds as follows:
H2O2 + NaCN = H2O + NaOCN
In case of the TISZA river the problem is complicated by expences and practical introduction of large quantity of peroxide homogenously into the whole wolume of the streaming water. Maybe it would be simpler to oxigenate cyanide in the streaming water with the air - letting water flow through artifically created series of obstacles. In the presence of air and UV portion of sun light the concentration of cyanide would be significantly reduced.
This is a similar process to that used in the wast water treatments aimed to reduction of its "criterion of quality" - the biological consumption of oxigen.
Good luck,
R.S.
Dear Ratislav,
Thank you for your answer. The average cyanide level was 100 higher than the LD50 value, and it is diluted along the river with elongation of the "cork" containing the cyanides. At the pH of the river the cyanide was mainly bound in complexes, not only cyanide (cyanide ion and HCN) but large amount of Cu(CN3)3(1-) type complexes were also present. The oxidation/aeration is a good idera , but only for the free cyanides. UV irradiation mentioned by you on the top surface also a good idea because that decomposes the cyanide complexes by photoylsis.
Aeration among the suggested one by you seems to be better than H2O2, because the H2O2 would be consumpted by the organic materials in the river and the sludge at the bottom. Thank you again for your kindly remark and answer.
Do not mention it, it´s OK. It might be useful to look at chemical tables to find which complex is more stabile thn Cu /CN/3 -1 .., and use a donor with which Cu complexes are more stabile.......
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