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- .. , <br />Page 11 <br />or obtain design Information. The results Indicated that WAD cyanide levels of 218 mg/I could be reduced <br />t to less than 10.0 mg/I. The Increase In total cyanide was due to sdublllzatlon of Iron and formation of the <br />stable Iron cyanide complex. The change In chemistry noted Indicated the need to examine each <br />application end each slurry Individually to determine potential changes In the slurry chemistry~ An overall <br />removal d cyanide of greater than 95 percent was achieved. The apparatus simulated a complete mix <br />' ' reactor: Alr flow rates of 80 and 100 L/mIrt'were employed along wrih 10 L slurry samples. <br />.: ~.. ; <br />Employing the data and basic knowledge of the process, a continuous flow pilot plant program was <br />' designed to Investigate the recovery of cyanide using eriher complete m1x reactors In series for stripping <br />towers. <br />' The plld plant program was undertaken to verify the laboratory results and to obtain the necessary design <br />Information for the full-scale cyanide recovery system. The slurry used In the pilot plant study Was obtained <br />from the Martha HMI Gdd Mlne located In the town of WaIhI, New Zealand. Tha slurry exhlbripd chemical <br />and physical ctlaracterlstlcs slmflar to those anticipated at the Gdden Cross Mine and provided pn excellent <br />continuous untreated teed for the p11ot plant program. The form of the WAD cyan'xie was predominantly free <br />and a basic pH was selected for the volatilization process. <br />' In the first phase of the study, the use of multiple complete mix reactors In series was Investigated, along <br />with varbus aeration periods and air flow rates. Course bubble flexcap diffusers were used to tacilriate <br />recovery of free cyanide and to minimize buildup of total dlssdved sdids and precipitates <br /> <br /> <br />1 <br />;:; , <br />:::~ <br /> <br /> <br /> <br /> <br />1 <br /> <br />The results of the aeration basin studies are summar'IZed In Tables 7 and 8. At slurry feed rates ringing from <br />0.5-2.2 ma/hr, air flow rates ranging lrom 2.4.0 m'/ma min, aeration periods ranging from 138-3.12 minutes, <br />and a slurry depth of 1.3m, WAD cyanide was reduced from 150-230 mg/I to 157 mg/I. THe results In <br />Table B Indicated that In multiple baffled systems of 3-5 complete reactors, the bulk of the cyanide removal <br />occurred wrihln the first hour of aeration regardless of air flow, pH, or Influent cyanide concentrations. <br />However, there was a marked difference In relative cyanide removal wrihin the first hour depending on the <br />air flow rate. No mechanical problems were encountered wrih the equipment or diffusers althqugh certain <br />deficiencies were noted In the actual battle construction. No buildup of chemical preclpriates here noted. <br />TABLE 7 <br />RESULTS OF THE CONTINUOUS FLOW PILOT PLANT STUDY USING COMPLETE MIX F4EACTORS <br /> Slurry Feed Influent No. of Total Aeration Effluent <br /> Ratg InOusnt WAD CN Alr Flux <br />= Slurry Depth Readora ~ Period WAD CH <br />Tr1al m /hr1 fOHI ~mM) maim <br />emin (m1 In Sedea (mini Imdll <br />1 1.7 8.0 230 4.5 1.3 1 f~ ~ 136 67 <br />2 1.7 0.8 150 4.5 1.3 1 13B 43 <br />3 2.2 0.6 228 4.6 1.3 1 106 67 <br />1 2.2 B.7 228 3.9 1.3 1 106 67 <br />S 1.7 B.7 196 4.4 1.3 3 138 60 <br />6 1.6 8.7 195 4.5 1.3 3 130 `u2 <br />7 2.2 B.0 168 2.4 1.3 3 106 84 <br />0 2.2 t0.0 1B2 4.S 1.3 5 B2 61 <br />B 0.5 10.0 207 4.5 1.3 5 312 26 <br />10 0.3 10.0 157 2.8 1.3 5 312 20 <br />71 0.5 70.0 766 4.5 1.3 S 312 23 <br />12 0.3 10.0 170 4.5 1.3 b 312 22 <br />1J 0.5 10.0 20.7 4.5 1.3 S 312 23 <br />14 0.3 10.0 179 6.2 1.3 5 312 18 <br />15 0.5 10.0 171 8.6 1.3 3 167 18 <br />18 0.5 B.0 161 4.3 i.3 S 312 18 <br />17 O.S 0.0 178 6.0 1.3 5 312 15 <br />