GENERAL47956

• Permit No: M1988112
• IBM Index Class Name: General Documents
• Doc Name: THE RECOVERY OF CYANIDE FROM SLURRIES
• Media Type: D
• Archive: No

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Pega 11
Employing the data and basic knowledge of the process, a continuous flow plot plant program was
designed to Investigate the recovery of cyanide using ehher complete mbc reactors In series or stripping
towers.
or obtain design Inforrnatlon. The results Indicated that WAD cyanide levels of 218 mg/I could be reduced
to less than 10.0 mg/I. The Increase In total cyanide was due to sdubllzatlon of Iron and formation of the
stable Iron cyanide complex. The change In chemistry noted Indicated the need to examine each
appllcatkx-ard each slurry IsldNldually to determine potential changes In the slurry chemistry. An overall
removal of cyanide of greater tharf 95 percent was achieved. The apparetus simulated a complete mbr
reactor: Alr flow rates of 80 and 100 L(mlrt'were employed along with 10 L slurry samples.
The plot plant program was undertaken to verify the laboratory results and to obtain the necessary deslgn
Information for the full-scale cyanide recovery system. The slurry used In the picot plant study Has obtained
from the Martha Hill Gdd Mlne located In the town of Waihl, New Zealand. The slurry exhlbrted chemical
~.`:• and physical characteristics slmlar to those anticipated at the Gdden Cross Mine and provided an excellent
continuous untreated teed for the pilot plant program. The form of the WAO cyanide was predominantly free
and a basic pH was selected for the volatilization process.
In the first phase of the study, the use of multiple complete mix reactors In series was Invest gated, along
with various aeration periods and air Flow rates. Course bubble flexcap diffusers were use'i to facilitate
recovery of free cyanide and to minimize buildup of total dissolved solids and precipitates
T.p
\:Y

The results of the aeration basin studies are summarized In Tables 7 and 8. At slurry feed rates ranging from
0.5-2.2 m'/hr, air flow rates ranging from 2.4$.0 m'/m= min, aeration periods ranging from 138312 minutes,
and a slurry depth of 7.3m, WAD cyanide was reduced from 150-230 mg/I to 157 mg/1. 1'he results In
Table 8 Indicated that In multiple baffled systems of 3-5 complete reactors, the bulk of the cyanide removal
occurred within the first hour of aeration regardless of air flow, pH, or influent cyanide coicentrations.
However, there was a marked difference 1n relative cyanide removal whhin the first hour depending on the ~ ~
air flow rate. No mechanical problems were encountered with the equipment or diffusers although certain
deficiencies were noted In the actual battle construction. No buldup of chemical precip{tates were noted.
TABLE 7
RESULTS OF THE CONT{NUOUS FLOW PILOT PLANT STUDY USING COMPLETE MIX REACTORS
Shirty fsW Influent No. of Total Aenlion Effluent
Rat
; Influent WAD CN Alr Flu= Slurry Depth Reactor Period WAD CN-
Tr1al Im
lhrl (oHl (mM) ma/m=emin (m) In Serlea lminl (mdn
1 1.7 B.6 200 1.5 1.3 1 r" ~ 178 67
2 1.7 9.6 150 1.3 1.3 7 776 4]
] 2.2 B.6 226 I.fi t.3 1 106 67
/ 2.2 B.7 226 ].9 1.] 1 106 67
5 1.7 9.7 19B 1.1 1.] ] 1]B 60
6 1.6 9.7 195 4.5 1.7 ] 170 52
7 2.2 B.B it+8 2.1 1.3 7 106 BI
B 2.2 10.0 1 B2 /.3 1.7 S 92 67
B 0.5 10.0 207 1.3 1.7 S 712 28
10 0.5 100 1ST 2.B 1.3 5 712 28
it 0.3 10.0 19B I.S 1.] 5 ]72 2]
72 0.5 10.0 170 1.5 1.] 5 012 22
10 0.5 t0.0 203 1.3 1.] S 712 ~
11 0.3 70.0 179 6.2 1.] S 072 16
15 0.3 10.0 171 fi.B 1.0 ] 167 16
t6 OS 9.B 164 4.5 1.] S ]12 19
t 7 0.5 B.0 176 6.0 1.] 3 012 13