My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
GENERAL47956
DRMS
>
Back File Migration
>
General Documents
>
GENERAL47956
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
8/24/2016 8:23:30 PM
Creation date
11/23/2007 3:58:14 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1988112
IBM Index Class Name
General Documents
Doc Name
THE RECOVERY OF CYANIDE FROM SLURRIES
Media Type
D
Archive
No
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
30
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
View images
View plain text
<br />Pays e <br />or a shallow aeration basin. The vdatllizatlon system is sealed to prevent escape of HCN Laden air and to <br />allow efficient recovery of cyanide. All configurations are applicable to eRher slurries or darHied sdutlons. <br />A strippng efficiency In the range of 90-99 percent Is possible. In the case of complete mbi reactors or <br />aeraton basins, coarse bubble diffusers are employed In the bottom of the reactors, and the reactors are <br />sealed to eliminate. release of HCN gas to the atmosphere. The use of diffusers provkJes air for agitation <br />of the sdutlon as well as stripping of the tree cyanide. Mechanical ag'rtatlon does not provide the necessary <br />turbulence to facilitate~strlpping of HCN:•*~': <br />The~iree cyanide produced through volatilization is entrained in an air stream, passed upflow through a <br />packed tower, and reabsorbed Into a caustic soution moving counter current to the air flow. The caustic <br />soution is then resumed to the metallurgical circuft for reuse. The pH of the caustic soution is maintained <br />In the range of 10.5-11.5. <br />Is free of recoverable free cyanide, K enters the reneutrallzatlon stage of the <br />to 9.0-10.5 viiih lime. to orecioitate residual meta~s <br /> <br />buffering capacity. With cyanide removed, the metals are released in free form into sdulion, allo~ng <br />precipitation to low levels as their stable and Insoluble carbonate and hydroxide complexes. The addition <br />of buffering capaciy is important in the event a slurry being treated exhibits the potential for acid generation <br />through sulf'xie ox{dation. The lime may be supplied as thickened sludge from other treatment processes <br />it present on site. The simplified chemistry of the process Is presented in the fdlowing reactions: <br />(t) Ca(CN), + H,SO, = 2HCN + CaSO, (acidification) <br />(2) M(CN)r + H,SO, = 2HCN + M"SO,-' <br />(3) HCN/H=0 =HCN/Air (volatilization) <br />(4) HCN + NaOH = NaCN + H,O (absorption) <br />(5) M" + 20H- = M(OH)i (precip8ation/reneutralization) <br />(6) Na,Fe(CN), + 2CuS0, = Cu,Fe(CN), (red/brown) + <br />2Na,S0, (ron cyanide ram~~val) <br />The process chemistry Indicates that the Initial phase of recovery Invdves conversion of CN- to HCN and <br />initiation of breakdown and of precipitation of neutral metal cyanide complexes. The extent of the <br />conversion dependent on the pH chosen for recovery and forms of cyanide being recovered. At very low <br />pH values, precipitation of Iron complexed cyanide occurs as the copper-iron cyanide conplex, which <br />accounts for the removal of this portion of the total cyanide. <br />PROCESS PERFORMANCE <br />As discussed previously, excellent overall stripping and recovery efficiencies of total and WAD cyanides from ~ ~ .. <br />barren and decant solutions are achievable by any of the recovery processes mentioned. In the wse of the ..: <br />three full-scale systems described above, overall removal efficiencies ranged from 92 to 99 pe~cent. In the ~ __... , <br />case of the Flin Flon Mine, the total cyanide level was reduced from 560 mg/I to 44 mg/I. The pertormance <br />of the Gdconda C.R.P. facllRy Is presented In Table 2. The initial total and free cyanide levels of 200 mg/I <br />and 10-30 mg/I were reduced to <5.0 mg/I and <0.50 mg/I, respectively. The residual cyanide levels were <br />reduced further once the treated effluent was passed through a carbon adsorption cdumn prior to <br />discharge. <br />In addition, the copper, nickel, and zinc concentrat(ons were all reduced to < 1.0 mg/I In the treated effluent. <br />The level of treatment obtained was consistent with that achievable by any chemical and/or biological <br />treatment process currently used In the mining Industry. The cyanide regeneration process also enhanced <br />the recovery of gdd from solution through carbon adsorption. <br />
The URL can be used to link to this page
Your browser does not support the video tag.