Proceedings of XXIV International Mineral Processing Congress, Beijing, 2008, pp. 2765-2773 Advances in Gold Ore Processing V. E. Dementyev, G. I. Voiloshnikov IRGIREDMET, Irkutsk, Russia Email: [email protected] ABSTRACT This paper presents a brief overview of some IRGIREDMET advances in gold hydrometallurgy. Original impulse-percolation technology and equipment for intensive cyanidation of gravity concentrates have been developed and introduced into industrial practice by IRGIREDMET since 1980s (RF Patents N1593250). The process is based on leaching using special hydrodynamic and reagent conditions providing high dissolution rate for coarse gold particles. Gold and silver are pre- cipitated from pregnant solution by cementation or electrowinning. There was also proposed an im- proved cementation method using zinc in a contact with electrically conductive material. The units including closed water recirculation, tails detoxification and semi-dry tails disposal were developed for the mines and operations without their own cyanidation facilities. IRGIREDMET is well experienced in gold adsorption technology using ion exchange resins and activated carbons. The comparison of CIL and RIL processes were done for a number of gold mines, for example for Sukhoi Log gold deposit. The properties of prospective foreign and domestic ad- sorbents including strong-base, bi-functional and weak-base resins as well as activated carbons were studied. The Institute has developed some adsorption/elution technologies and equipment, such as a two stage RIP adsorption technology for gold/silver ores, an improved technology for gold elution from loaded resin and carbon, electrowinning cells for gold recovery from RIP and CIP eluates etc. Large scale “Resin In Pulp” tests using weak-base resin were finalized and process design criteria were developed. Gold plant design is on progress at the moment. Improved technology for carbonaceous (preg-robbing) gold ores was developed. It was tested for some gold deposits including Sukhoi Log. It allows to overcome preg-robbing activities of ores treated and to improve dramatically performance of cyanidation and adsorption circuits. The studies on refractory gold ore treatment including bio-oxidation, pressure oxidation, roasting and ultra-fine grinding were conducted. Heap leach technology was tested and introduced by Irgiredmet for a number of Russian mines. Zinc cementation, activated carbon and ion-exchange resin adsorption were used for gold recovery from pregnant heap leach solutions. The options including combined technology “Heap leach/ RIL or CIP” for clay ores were also developed and tested. The plant using developed technology is at construction stage now. The study on In-Situ gold leaching was conducted. The comparison of different gold lixiviants for this purpose was carried out. Gold recovery from pregnant leach solution by activated carbon and anionite including gold elution from loaded adsorbents etc. was also studied. In 2000 the In-Situ leaching technology was commissioned at Maminskoye gold deposit (Ural). The technologies for treatment of complex ores and by-products were proposed. For example, the technology of gold, silver, copper and zinc recovery from calcines after sulphuric acid produc- tion was developed. Keywords: Gold; Preg-robbing; Complex and refractory ores; Intensive cyanidation; Adsorption; Activated carbons; Anionites; Heap leaching; In-situ leaching; Equipment for hydrometallurgy 2765 INTRODUCTION vents losses of fine gold with slimes. The inten- sive cyanidation unit was developed for mines For many years IRGIREDMET (estab- and operations which have no their own cyani- lished in 1871) functioned as the head state re- dation facilities. Of course it may be easily used search center for gold mining industry in Russia for cyanidation gold plants too. and the former Soviet Union and took an active The Irgiredmet unit for intensive cyanidation part in the majority of Russian gold and dia- consists of a cyanidation reactor made as a cone mond projects. At present Irgiredmet is an Open (pyramid), a circuit for a processing of pregnant Joint Stock Company dealing with a full range leach solutions by zinc precipitation or electro- of services including research and development, winning and a tails detoxification unit. The project design, engineering, equipment and re- reactor for intensive cyanidation have no mov- agent supply etc (from geology to gold refinery ing parts, therefore it is simple and robust in and tails detoxification). Since its foundation operation (Fig. 1). Concentrate grains are mixed Irgiredmet has started to develop improved by a flow of leach solution pumped by short technologies and equipment for gold recovery. impulses. Intensive mixing and gold leaching Some of this developments are described below. occur in the bottom of the reactor. Superficial INTENSIVE CYANIDATION OF GRAVITY velocity of solution in the upper part of the CONCENTRATES reactor is much lower therefore concentrate particles are held inside the reactor. The leach In 1980s Irgiredmet developed a technology solution from the reactor overflows to a sump and equipment for intensive cyanidation of non- and after its filling is automatically fed by a ground gravity concentrates which we call the pump to the leach reactor. Solution is circulated intensive cyanidation unit. through the system during a sufficient period for Advantages of the unit developed are its gold leaching. The concentrate is treated at op- simplicity, high gold recovery, closed water timum parameters such as concentration of cya- recirculation, use of the efficient technology of nide, leach time, mixing intensity, frequency of tails detoxification and semi-dry disposal which impulses and duration of settling of a concen- meet the demands of Russian environmental trate slurry to provide leach efficiency not less legislation (Mullov, Rashkovsky, 1993). Pre- than 90% ~ 95 %, even without the use of leach liminary washing of concentrate to remove aid reagents. slimes is not required as the proposed unit pre- Fig. 1 Intensive cyanidation scheme Electrowinning cells designed by Irgiredmet are used for gold precipitation from pregnant 2766 leach solutions. Irgiredmet also proposed an for cyanidation, processing of pregnant solu- improved cementation method using zinc in tions and drying and smelting of precipitates - contact with electrically conductive material. no more than 2~4 kWh per ton concentrate. Gold precipitates generated by this method Irgiredmet intensive cyanidation units were contain not less than 50 % of gold and may be supplied to 11 Russian gold operations includ- easily smelted to Dore metal. ing Samartinsky gold plant, Buryatia; Valunisty The unit provides low power requirements mine, Chukotka and others. (Fig. 2) Fig. 2 Intensive cyanidation unit view GOLD ADSORPTION TECHNOLOGY disadvantages (Table 1). So the final decision USING ION EXCHANGE RESINS AND on adsorbent selection has to be done on the ACTIVATED CARBONS base of economical evaluation results. The method of gold elution from loaded car- Irgiredmet has a good experience on gold bon by alkaline solution under pressure was adsorption technology using ion exchange re- developed in cooperation with Irkutsk Technical sins and activated carbons (Dementyev, Voi- University. The advantages of the developed loshnikov, 1998). Both adsorbents were com- elution process are the high rate and high gold pared for processing of ores, concentrates, recovery (duration of the process is about one bio-oxid- ation products etc. The comparison of hour; residual gold loading of eluted carbon −50 CIL and RIL processes was done for some gold g/t) and absence of cyanide in eluent (Table 2). mines, for example for Sukhoi Log gold deposit. The CIP technology based on the above men- The properties of prospective foreign and do- tioned elution method was successfully imple- mestic adsorbents including strong-base, mented at Lebedinsky plant (Aldanzoloto bi-functional and weak-base resins as well as Company, 1984), at Samartinsky plant (Buryat- activated carbons were studied. The Institute zoloto Company, 1998), Valunisty mine (Chu- has developed some adsorption/elution tech- kotka), Novo-Kochkarsky plant (Ural) and oth- nologies and equi- pment, such as a two stage ers. RIP adsorption technology for gold/silver ores, There was designed a column type reactor an improved technology for gold elution from for cyanidation and adsorption processes oper- loaded resin, electrowinning cells for gold re- ating as a plug-flow reactor instead of stirred covery from RIP and CIP eluates etc (Demen- tanks (Fig. 3). It is a vertical column divided by tyev, Voiloshnikov, 2005). horizontal plates of special design into several Both adsorbents have their advantages and sections. The column reactor allows to eliminate 2767 Table 1 Comparative characteristics of activated carbons and anion exchange resins Adsorbent type Characteristics activated carbon anion exchanger Sensitivity to ion composition of pulp (solution) treated lower higher Sensitivity to availability of organic compounds lower higher Particle size (size of screen aperture used)/mm +1.0 +0.5 Abrasion hardness/% lower (85~90) higher (>96) Adsorption kinetic slower faster Bulk density/(kg/L) 0.5 0.33 lower higher Adsorbent cost (1,700~2,500 $) 10,000~12,000 $ Necessity of thermal reactivation present no Specific gravity of wet particle (important for use column with 1.4~1.5 1.1 fluidized bed of adsorbent)/(g/cm3) H SO , CS(NH ) , Reagents used for gold elution NaCN, NaOH 2 4 2 2 NaOH Elution temperature/oC 95~175 60 Elution column constructive material Steel Titanium or rubber lined Adsorbent losses/(g/t) higher lower Gold recovery from flotation concentrates improved - Environmental problems (tails detoxification and others) easier more complicated Table 2 Comparative parameters of gold elution methods Elution method Process Zadra (USA) IPS Irgiredmet parameters AARL (RSA)* under pressure ** ambient pressure (Australia) (Russia) Presoaking necessary no no no no 2%~3% NaCN Presoaking solution − − − − 2% NaOH Bed volume/BV 0.6 − − − − Duration/h 0.5~1.0 − − − − Temperature/°C 110~120 − − − − Gold elution High quality 0.2%~0.5% NaCN 0.1%~0.3% NaCN 2%~4% 0.2%~0.4 % Eluent composition softened water 1%~2% NaOH 1%~2% NaOH NaOH NaOH (<300 mg/L Na) Temperature/°C 110~120 120~127 93~95 145~155 165~175 Eluent flowrate/(BV/h) 0.8~2.7 2.1~2.6 1~2 2~2.5 10 Duration/h < 8 13~20 48~72 11~14 1 Number of BV 5~10 40~50 >50 25~35 8~10 Reagent consumption/ per 1 t of carbon NaCN/kg 60 (82.5) 30 >30 − − NaOH/kg 35 (51.3) 60 >60 50 40~80 Power/kW h 1500 (2883) 3533 >3500 1000~1900 2160~2880 short circuiting of feed to discharge point. It at Olimpiada (RIL-process, Krasnoyarsk Re- was tested in 1987 at Sovetsky gold plant gion) and Novo-Kochkarsky gold plants (CIL- (Krasnoyarsk Region) and commissioned later process, Ural) (Fig. 4). Use of columns allows 2768 to decrease the number of equipment units in comparison with conventional stirred tanks for the same gold recovery and gold adsorbent loading. Resin losses in RIL- process using the column reactor were decreased from 3%~5% down to 0.8 % due to more “delicate” agitation in comparison with air agitated adsorption tanks (Pachukas). Detailed design drawing were developed for column reactors with capacities of 20 m3, 40 m3, 100 m3, 210 m3 and 400 m3. Electrowinning cells for gold deposition from acidic thiourea eluates generated during gold elution from loaded resin and alkaline cya- nide eluates from carbon adsorption technology were developed. The peculiarities of the elec- trowinning cells are as follows: cathode preci- pitates are generated as slimes which allow to discharge precipitates without stoppage of elec- trowinning process and to achieve 96%~98% gold recovery per pass (20~30 minutes). Fig. 3 Column type reactor Fig. 4 CIP column type reactor – capacity 210 m3 each (Kochkarsky gold plant, Ural) Electrowinning cell with the cathodic surface type of the cells are made as stainless steel area of 120m2 and the capacity of 2 m3/hour plates and for the second type as stainless steel was developed for RIP eluates. Anodic and ca- screen. Plated cathode electrowinning cells are thodic areas are devided by cation exchange used at Samartinsky gold plant (Buryatia) and membrane to prevent thiourea oxidation. Sul- Kochkarsky gold plant (Ural). Screen cathode phuric acid solution is used as anolite. Electric electrowinning cells with cathode surface area current for cell is from 1000 A to 2000 A. The of 250 m2 and capacity 2~3 m3 / hour are used designed cells were used at Karamkensky gold at Valunisty mine (Chukotka). plant (Magadan Region) and are in use at Mno- Large scale “Resin In Pulp” tests using govershinny and Olimpiada RIL plants. weak-base resin were finalized and process de- Two types of electrowinning cells were de- sign criteria were developed. Gold plant design signed for CIP eluates. The cathodes for first is on progress at the moment. 2769 REFRACTORY GOLD ORE of the flotation concentrate (Fig.5). The total TREATMENT gold mass in the recycling products was about 1 % of the ore feed grade. Some of this gold Improved technology for carbonaceous was recovered during ore processing. The total (preg-robbing) gold ores gold recovery from ore with the head grade of The refractory ores often contain naturally- 0.8 g/t was 83.9 % including 53 % from the occurring carbonaceous material which can ad- high-grade concentrate and 30.9% by CIL of sorb gold-cyanide complexes from solutions. In gravity middlings and intensive cyanidation Russia 30 % of the total gold ore reserves are tailings. The gold loading onto the activated made up of these refractory ores. carbon from CIL-process was 6.500 g/t. The following methods were proposed to Recleaning of flotation concentrate by cyc- treat the preg-robbing ores depending on their loning and flotation allows significantly im- preg-robbing activity: prove the indices of hydrometallurgy for con- centrates. The test results showed that the pro- • direct cyanidation under the special condi- posed technology can be efficiently used for tions which completely or almost com- refractory carbonaceous gold ores including pletely prevents gold adsorption from solu- low-grade ores. tions by the carbonaceous material (Lodei- Bio-oxidation, pressure oxidation, roasting schikov, 1998); and ultra-fine grinding • chemical (fast chlorination) or thermo- chemical (roasting) oxidation of the car- Irgiredmet has conducted extensive multiyear bonaceous material with subsequent cya- study on gold recovery from refractory ores and nidation (Lodeischikov, 1999); concentrates by different methods (bio-oxida- • carbonaceous material extraction from the tion, pressure oxidation, roasting and ultra-fine ore by mechanical processing of the ore grinding). The results was summarized in mon- including classification, desliming and flo- ograph (Lodeischikov, 1999). tation to produce low-grade products with HEAP LEACH TECHNOLOGY subsequent cyanidation. Heap leach technology was tested and intro- Test results and gold plant practice showed duced by Irgiredmet for a number of Russian that preg-robbing carbonaceous ore slimes par- mines (Dementyev, Druzhina, Gudkov, 2004). ticles of less than 0.01 mm which are amenable Zinc cementation, activated carbon and to overgrinding can be removed by classifica- ion-exchange resin adsorption were used for tion (desliming) (Lodeischikov, 1999). gold recovery from pregnant heap leach solu- High gold recovery from some preg-robbing tions. The options including combined technol- gold ores and concentrates can be achieved by ogy “Heap leach/RIL or CIP” for clay ores were cyanidation using organic cyanides, surfactants also developed and tested. It consists of ore (kerosene, cresylic acid, combustible oils, ace- disintegration into a slime and sand fractions tone etc.) and some chemical reagents which are which are treated separately (the sands - by used for gold elution from pregnant activated heap leaching and slimes - by RIP or CIP). The carbons. plant using developed technology is at construc- Irgiredmet JSC developed an improved tion stage now. technology of processing and cyanidation of IN-SITU GOLD LEACHING concentrates produced from preg-robbing ores. This technology was tested using ores of a Rus- The innovative technology for gold recovery sian gold deposits (Dementyeva, Mullov, Vino- from hard rock and placer deposits which are kurova, 2007). too low in grade to justify mining and transpor- The developed technology of flotation con- tation expenditures is In-Situ leaching. centrate recleaning by cycloning/flotation al- Irgiredmet has conducted the study on lowed the reduction in the preg-robbing activity In-Situ gold leaching (Panchenko, Dementyev, as well as the 2.5 % reduction in the mass yield Khmelnitskaya, Lodeishikov, 2003). The com- 2770 Fig. 5 Ore concentration flowsheet including flotation concentrate recleaning parison of different gold lixiviants for this pur- In 2000 IRGIREDMET in cooperation with pose was done (Lodeischikov, Dementyev, the Ural Mining and Geological Company de- Khmelnitskaya, Chikina, Lanchakova, 2006). veloped process design criteria as well as Gold recovery from pregnant leach solutions by project design and commissioned into pilot op- activated carbon and anionite including gold eration the in-situ leaching technology by elution from loaded adsorbents etc. was also oxychloride solutions from Maminskoye depo- tested. sit ores (Ural) (Fig. 6). The basic criteria required for an under- Maminskoe gold oxidized ore deposit was ground deposit to be considered suitable for chosen as the object for In-Situ leaching as it is leaching in place are as follows: ore body must ideally suited for this purpose due to its mineral be enclosed between impermeable strata that composition and hydrogeology. The ore re- will prevent losses of solution; it must be per- serves within the In-Situ block are 90,000 t with meable to leach solution. Two technologies are average gold grade of 0.7 g/t. used: spraying when ore body is exposed and The capacity of pilot plant operation was 15 injection when it is buried. m3/hour. Gold concentration in pregnant solu- 2771 Fig. 6 In-Situ gold leaching process scheme tion is 0.12 ppm~0.13 ppm, chlorine consump- concentrates preliminary hydrochloric acid tion is 3.5 kg per 1 g of recovered gold. treatment allows to achieve additional gold re- In comparison with conventional methods of covery 1.8% ~ 3.5%, silver recovery 22.7% ~ gold ore processing In-Situ leaching allows to 24.4%, bismuth 15.8% ~ 16.9%. decrease investment costs in 2~4 times and to Initial data for a bank feasibility study and reduce the cost of gold production in 1.5~2.0 plant designing were developed from test re- times. sults. The raw material for In-Situ leaching are Magnetic separation, flotation, bioleaching, small-sized and buried placers, cut-of-grade cyanide, thiourea, sulphite leaching were tested gold ores etc., which can not be treated cost to utilize valuables from burnt pyrites. The effectively by conventional methods. technology for valuables recovery from burnt Irgiredmet Institute cooperates on In-Situ pyrites was developed (Khmelnitskaya, Mullov, leaching technology with JSC “Geoprid”, Komlev, Lanchkova, 2008). It includes water “Northern” gold company, JSC “Gagarka- washing of soluble compoments by CCD Au-PV” process, lime treatment of washed residue with air sparging, gold and silver cyanidation. Cop- THE TECHNOLOGIES FOR per and zinc are recovered from wash solution, TREATMENT OF COMPLEX ORES AND gold and copper – from cyanide solution. BY PRODUCTS SX/EW technology is used for copper recovery. The studies on testing and development of The technology developed allows to recover technology for gold-bismuth ore treatment were 54 % of gold, 45 % of silver, 30% of copper and conducted (Khmelnitskaya, Beskrovnaya,2007). 50 % zinc. As a results a process flowsheet including grav- Final tails may be used as iron bearing ma- ity, flotation, hydrochloric acid leaching of terial in cement industry. combined concentrate and its subsequent cya- CONCLUSIONS nidation was recommended. The saleable prod- ucts generated were the following: bismuth High world gold price and depletion of free bearing cathode precipitate (71%~79 % of Bi) milling ores is stimulated development of im- and Dore metal. Overall gold, silver and bis- proved technology and equipment for gold re- muth recoveries were 84.8% ~ 86.5 %; 63.2% ~ covery. Brief overview of Irgiredmet develop- 64.9% and 75.8% ~ 76.9 % respectively. ments on gold metallurgy is presented. It in- In comparison with direct cyanidation of cludes in particular the intensive cyanidation of 2772 gravity concentrate, adsorption/elution technol- 245-250. ogy and equipment for RIP and CIP processes, Khmelnitskaya, OD, Mullov,VV, Komlev, MY, Lanchkova, OV, improved technology for treatment of refractory 2008. In press. A complex technology of pyrite cinders and complex products (preg robbing ores, gold/ processing. Paper in preparation for Proceedings of the bismuth ores, burnt pirytes etc.), In-Situ-Lea- XXIY IMPC. ching for low grade gold ores etc. The majority Lodeischikov, VV, 1998. Main Irgiredmet’s test and develop- of mentioned above advances are used effi- ment results on gold recovery from Sukhoi Log ores. Irgi- ciently in gold mining industry of Russia. redmet Proceedings 125 Years Anniversary Edition, pp. 417-435 (Irgiredmet: Irkutsk). REFERENCES Lodeischikov, VV, 1999. Technology of gold and silver recovery from refractory ores, Irgiredmet: Irkutsk , pp 464-484. 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