Gold mine cyanide wastewater acidification recovery method 1

N , AgSCN , Zn2Fe(CN)6 , Pb2Fe(CN)6, etc.

2.3 HCN gas absorption

  
The HCN- containing gas obtained by degassing the acidified wastewater with a gas (called a carrier gas) is neutralized with a NaOH absorption liquid to form a neutralization reaction to form NaCN . The reaction is completed in an instant, and since the HCN is a weak acid, the absorption liquid must be kept constant. The alkalinity can ensure the complete absorption. Generally , the residual NaOH in the NaOH absorption liquid is controlled in the range of 1% to 2% , and the absorption reaction is as follows:

  NaOH+HCN(g)=NaCN(aq)+H 2 O

  The
price of NaOH is much higher than that of CaO . Therefore, there is a use of lime milk instead of NaOH , but measures to prevent fouling and block the absorption tower.

  2HCN+Ca
( OH ) 2+Ca ( CN ) 2 +H 2 O

After the HCN
is absorbed, the carrier gas is recycled, and its advantages are as follows:

 
1) The carrier gas is originally air, and the acidic component such as CO 2 reacts with the alkali in the absorption liquid to consume alkali. If it is recycled, the alkali solution is no longer consumed.

 
2) When the carrier gas is recycled, the oxygen in the carrier gas is less and less, and the cyanide is prevented from being oxidized during the acid stripping process.

 
3) If the carrier gas is not recycled, due to the contact of the carrier gas with the liquid phase, the humidity is very large and contains a small amount of HCN , which can only be discharged to the outside, but a large amount of fresh air is introduced in the winter, and the blow-off requirement is required. Temperature, inevitably consumes additional energy and wastes energy, so the carrier gas is generally recycled.

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