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By D. Kidby, A. Briggs

"Vitrokele ™ is a synthetic adsorbent, using chelating groups on large polystyrene beads, developed in Canada over 7 years ago, and first commercialised in 1985 to recover noxious metals from plating wastes.Pilot plant trials have been performed in Australia and Canada to demonstrate the recovery of cyanide and removal of metal cyanide complexes from gold plant effluent using Vitrokele1 M 912. The pilot plants comprise a simple adsorption train (similar to a CIP circuit) followed by complete elution facilities, so that loaded Vitrokele™ can be stripped and returned to the adsorption circuit.An account of these campaigns is provided, showing the reduction of total CN levels from over 200 ppm to less than 0.5 ppm and Cu levels from approximately 100 ppm to less than 0.3 ppm in treated tailings.Comparisons between pilot plant results and laboratory test data are given and probable future work on the process and its application to the gold mining industry is discussed.INTRODUCTIONThrough millions of years of evolution, life forms have developed specialised molecules with exceptionally high affinity and selectivity for various metals such as iron, cobalt, zinc and copper.In the early 80's professors at the Faculty of Medicine of McGill University engaged in research on the extremely efficient ways that living cells captured trace metals essential for life.As research progressed, it became evident that the special molecules used by biological systems to capture metals could be synthesized to capture selected metals with similar efficiency from water or other solutions.The technology was first commercialised in 1985 to recover noxious metals from plating wastes with compositions applying the special molecules (chelating groups) on vitreous particles (hence Vitrokele™). To date approximately three commercial Vitrokele™ plants have been installed for treating plating waters in Ontario and Quebec."

Jan 1, 1992

By Dean Lindsay, Inna Dymov, Mariam Melashvili, Jim Smolik, Chris Fleming

"This paper presents results from the proposed cyanide detoxification circuit for Seabridge Gold’s KSM project. The proposed flowsheet uses a two-stage CCD (counter-current washing/decantation) circuit to transfer the flotation products CIL(carbon-in-leach) barren solution to a SART process (Sulphidization, Acidification, Recycling of precipitate, and Thickening of precipitate) to recover copper and free cyanide from the copper cyanide complex. The SART barren solution is then treated by an AVR process (Acidification, Volatilization of HCN gas, and Reneutralization) to concentrate the cyanide that was liberated in SART for recycling to leach. The washed CIL barren pulp (the CCD underflow) is treated with the SO2 /Air process to oxidize residual cyanide.The goal of this complex flowsheet is to recover and recycle as much cyanide as possible and produce a final effluent containing less than 0.5 mg/L copper and CNWAD at the lowest cost. The SO2/air process is capable of achieving low residual CNWAD (<1 mg/L) in the final product, but the persistence of aqueous copper above the target level has been detected in the treated solution in some instances. The expected high concentrations of copper and cyanide in the KSM CIL barren ( >200 mg/L each species) and the difficulties this might create for the SO2 /air process was a key factor in the decision to consider including the washing, SART and AVR steps in the project flowsheet.The target concentrations of CNWAD and Cu were readily achieved after aging the SO2 /air treated pulp, as would occur in a tailing or polishing pond. This suggests no additional treatment will be required to sustain low levels of these species in the final plant effluent."

Jan 1, 2015

By M. Hames, K. Larmour-Ship, B. Grinbaum, E. Buchalter, R. Hackl, B. Wassink

Sodium cyanide continues to be the lixiviant of choice for gold dissolution. Many gold ore-bodies contain a significant amount of cyanide-soluble copper which increases the cost of processing due to high cyanide consumption and high cyanide destruction and disposal costs. Several cyanide destruction processes are in use today, however, there are just a few cyanide recovery plants operating. A solvent extraction process to recover cyanide has been developed which utilizes the organophosphorous extractants Cyanex 923, di-butyl-butyl-phosphonate (DBBP) or tri-n-butyl phosphate (TBP) in Bateman Pulsed Columns. Copper cyanide species are first converted to hydrogen cyanide (HCN) by acidification, with or without sulfide addition. HCN is extracted by the organic and stripped using a suitable base (eg. NaOH) resulting in a high strength cyanide solution (eg. NaCN) for recycle to the gold recovery process. Continuous pilot plant testwork on HCN extraction using a 40 mm diameter Bateman Pulsed Column demonstrated a cyanide recovery of greater than 99% with final levels of cyanide in solution of less than 10 ppm. These results illustrate the potential of this technology to recycle cyanide and to detoxify final effluent streams.

Jan 1, 2005

By P. A. Riveros, J. Binvignat, V. M. McNamara, D. Koren

The recovery of cyanide from a gold mill solution containing high levels of copper (400 mg/L to 900 mg/L) using the AVR process was evaluated. It was determined that acidification to pH 2 to 3 provides a suitable balance between HCN generation, copper precipitation and acid consumption. A short pilot plant campaign showed that ~75% of the feed WAD cyanide was recovered while the remainder precipitated along with copper upon acidification. The acid consumption averaged 3.5 g H2SO4 per litre of solution. The copper precipitate, consisting mostly of CuCN and CuSCN, was readily separated from the solution by gravity. The volatilization of HCN in countercurrent packed columns averaged 98.7% efficiency. Reabsorption of HCN was practically 100% in NaOH solutions and slightly lower in a lime slurry. Basic volatilizer design parameters applicable to a large-scale operation were determined, including the Henry’s Law constant and the mass transfer coefficient of HCN gas.

Jan 1, 1998

By R. S. Shoemaker, F. W. McQuiston

The principle of cyanide recovery or regeneration of cyanide from solution, be it a weak wash or a foul solution, is by acidulation. All or part of the cyanogen is converted thereby into hydrogen cyanide which is fixed by an alkali (generally lime) and returned to the cyaniding system (the Mills- Crowe process). The solution is made acid by bringing it into contact with sulfur dioxide. The acidified solution is stripped in a packed tower by a counter flow stream of air in which the air and the solution are brought into intimate contact. The air leaving the tank charged with hydrogen cyanide is then passed to another tank in which it is mixed with an alkaline solution, the latter absorbing the HCN and leaving the accompanying air clean for reuse in removing more HCN from the acidified solutions. Of the recoverable cyanide, 9770 is usually recovered in a three-unit disperser tower system. When there is a considerable content of copper, the solution is made acid following standard procedure; however, the HCN is not removed until the copper is reduced by regeneration. Copper removal at this point may be as high as 90%. After reduction of the copper, the acidified solution then is contacted with a lime solution which brings down calcium sulfate as a second step. The silver, gold, and copper are recovered in the form of a precipitate which can be shipped to a smelter. At the Hudson Bay Mining and Smelting Company, Ltd., most of the precious metals have been recovered in the copper and lead concentrates, but it has been found profitable to submit the flotation tailings to a scavenger cyanide treatment for the recovery of exposed gold contained in pyrite rejected during flotation. Due to the fine particle size, maximum dissolution is achieved in a four-hour contact period. In the cyanidation plant, the thickened flotation tailing at 70% solids is given a four-hour agitation in weak calcium cyanide solution and filtered. Filter cake is repulped and discharged either to the tailing storage area or to the mine as backfill. Clarification, de-aeration and precipitation of pregnant solutions are carried out in a standard Merrill-Crowe unit. Typical analysis of precipitate is as follows: Au, 0.47%, Ag, 4. 88%; Cu, 46.0%; Zn, 13. 8%. Cyanicides in the form of copper minerals limit the reuse of barren solution. To recover the substantial quantities of cyanogen chemically combined with base metals in this solution, a cyanide regeneration plant is in operation. The barren solution is acidified with sulfuric acid in a spray tower where an upward current of air from a blower sweeps the liberated hydrocyanic acid gas to an adsorption unit where it meets a fine rain of lime suspended in plant solution with which it combines to form calcium cyanide. The lime--water solution carrying calcium cyanide is reused in the cyanide circuit. The return gases are drawn into the blower and back to the disperser tower thus

Jan 1, 1975

By N. D. Jagger, I. M. Arbuthnot

The recovery and destruction of cyanide in gold tailings is currently a topic of great interest for both financial and environmental reasons. The environmental problem is particularly important in the U.S.A. at present with the environmental lobby waging a campaign to eliminate the problem of migratory birds dying after drinking tailings dam wate. Tough legislation with severe fines and jail sentences for company executives have been introduced in several states for exceeding cyanide limits. To reduce cyanide levels in tailings dams chemical treatment, including acidification, alkaline chlorination, the INCO sulphur dioxide oxidation process and the Degussa hydrogen peroxide process amongst others are being. used. In addition several processes are at various stages of development for the recovery of residual cyanide from gold tailings. Among these is the process developed by Cyprus Gold and pilot tested by DSIR Industrial Development. This process uses air to strip cyanide from the acidified barren pulp and will be used at Cyprus Gold Mines Golden Cross Mine on the Coromandel Peninsula in New Zealand (Fricker & OWers 1990).

Jan 1, 1991

By H. Soto, J. Jara, F. Nava

A method has been developed to recover cyanide and copper from cyanidation effluents contaminated with thiocyanate and copper-cyanide complexes. Copper is precipitated as copper thiocyanate or as copper cyanide depending on pH and the concentrations of thiocyanate and cyanide present in the effluent. The copper precipitate presents good dewatering characteristics and can be easily separated from the effluent by thickening and filtration. The solution containing the bulk of the cyanide is then oxidized with ozone to transform the remaining thiocyanate into cyanide. This results in a regenerated solution rich in free cyanide that can be recycled to the cyanidation process. Careful control of the pH of the solution is required. First pH of the effluent is lowered to optimize the precipitation and oxidation stages, then the pH is restored to an alkaline value to regenerate the cyanide solution. Recoveries of over 96% copper are obtained. Free cyanide in the regenerated solution corresponds to up to 160% of the total cyanide contained in the original impure effluent. (The balance being accounted for by the cyanide obtained by the oxidation of thiocyanate). The efficiency of the thiocyanate oxidation stage is 85% to 90%. The method has been demonstrated at bench scale with effluents of various cyanidation plants of northern Quebec. A preliminary economic evaluation indicates that the procedure would be profitable for effluents rich in copper and thiocyanate. This is the case for most barren bleeds of Merrill Crowe and heap leaching operations and also certain CIP tailings of gold ores containing copper impurities. Environmentally the procedure is a better alternative than the current detoxification methods based on the oxidation of cyanide that do not allow for copper recovery and that have difficulties in producing a final effluent with acceptable levels of contaminants such as ammonia, thiocyanate and copper.

Jan 1, 1996

By H. Soto, J. Jara, F. Nava

A method has been developed to recover cyanide and copper from solutions containing copper complexes and thiocyanate. Copper is precipitated as copper thiocyanate or as copper cyanide depending on pH and the concentrations of thiocyanate and cyanide in the effluent. The copper precipitate assays over 50% copper and presents good dewatering characteristics. After settling it can be separated from the effluent by filtration. The solution containing the bulk of the cyanide is then oxidized with ozone to transform the remaining thiocyanate into cyanide. This results in a regenerated solution rich in free cyanide that can be recycled to the cyanidation process. Careful control of the pH of the solution is required. First, pH of the effluent is lowered to optimize the precipitation and oxidation stages, then the pH is restored to an alkaline value to regenerate the cyanide solution. Recoveries of over 96% copper and cyanide were obtained in laboratory tests using industrial solutions. With this procedure, cyanocidic gold/copper ores could be treated economically by heap leaching, since the cyanide consumed by the copper impurities could be regenerated at very low cost (most of the cost of cyanide regeneration would be compensated by the copper credits). In order to achieve this, a bleed of the barren solution could be treated by the proposed method, and then recycled to the leaching step. The volume of solution to be treated should be large enough to keep a cyanide/copper molar ratio higher than 3:1. This would assure that copper does not cause undue interferences in the leaching or the carbon adsorption stages. If the thiocyanate content is low, the oxidation stage can be avoided, and the solution can be recycled to the leaching stage directly after the solid-liquid separation stage.

Jan 1, 1997

By A. V. Faiberg

Currently, the interest to conditioning of cyanide-bearing recycled solutions with high-grade of base metals, in particular, copper has significantly grown. This can be explained by two major factors. Firstly, there are strict regulations on cyanides amount in tails and higher cost of detoxification processes. This problem can be easily solved during the ore treatment using the conditioning of solutions and water recycling. Secondly, the presence of other metals minerals which react with cyanide during gold leaching resulting in high cyanide consumption. The presence of copper is a major problem. Many copper minerals react with cyanide with the formation of cyanide complexes-Cu(CN)2-, Cu(CN)32- and Cu(CN)43-. One mole of copper consumes 2-4 moles of free cyanide. Availability of cyanide-soluble copper minerals has deleterious effect on gold leaching (gold recovery, cyanide consumption, tails detoxification, efficiency of gold elution and electrowinning). The precipitation of copper from the solutions improves gold recovery by CIL. The removal and recycling of cyanide allowed the reduction of cyanide addition to the process. The recycling of spent cyanide-bearing solutions based on the removal of copper and the return of cyanide bound in complex compounds for leaching process is an optimal way of solving the problem of gold-bearing copper ores treatment. By using the technology, an adverse impact onto gold recovery process is eliminated and at the same time reducing the cyanide consumption. Today, processes and methods of high-grade copper leaching solutions conditioning before and after gold recovery have been developed, which combine two ways of copper recovery: as a saleable product and cyanide to recover gold and reduce total operating costs. They are Cutech, MNR, SART, Cyanomet, AuGment, Vitrokele, Hannah and Cyanisorb. At the same time, these technologies have not been studied enough and described in literature. Data on parameters and operating conditions as well as introduction is not available. The conditioning technology of recycled solutions developed by IRGIREDMET JSC allows copper to be recovered as high quality concentrate and at the same time free cyanide regeneration in the recycled solution which is amenable to gold leaching. This technology was commercialized at a mine in Kazakhstan in 2008. The removal and recycling of cyanide does not require additional cyanide and is cost-effective. More cost-efficiency is achievable through selling copper concentrates, closed water cycle without the detoxification of effluents and enhanced gold recovery by CIL and cathode quality.

Sep 1, 2012

By C. W. Lawr

THE ores mined by the Santa Gertrudis Co. at Pachuca, Mexico, are mainly silver-bearing; they also yield some gold and carry a little copper. Strong cyanide solutions are used to dissolve the silver and gold, and the mechanical loss of cyanide at the tailings filter has been considerable. Prior to the year 1923, the pulp, after agitation, was given a 35 to 37-min. wash with barren solution in a Butters-type leaf filter; the discharged slime cake was repulped and pumped into eight Merrill self-sluicing slime presses in which the slime was given a further wash with barren solution for 25 to 35 min., followed by a 10-min. water wash. At that time the barren solution titrated around 0.350 per cent. free KCN and 0.500 per cent. total KCN. (Aero brand cyanide is used.) It can readily be seen that a 10-min. water wash would leave considerable cyanide in the filter cake, which of course was a total loss. This averaged 0.522 kg. (1.15 lb.) KCN per ton of solution. As the daily discharge to. the dam was 1600 tons1 of slime of a 2: 1 ratio of liquid to solid, the value of this mechanical loss of cyanide was an important item and its recovery held alluring possibilities.

Jan 1, 1929

By A. Khodadadi, M. Abdolahi, P. Taimory

Cyanide is used by the mining and chemical industries in tremendous quantities without attention being given to its hazardous properties. The use of cyanide compounds in mining is one of the most important environmental issues for the mining industry due to the acutely toxic properties of many cyanide compounds to humans and aquatic life. Cyanide tends to react readily with most other chemical elements, producing a wide variety of toxic, cyanide-related compounds and because cyanide is carbon based an organic compound it reacts readily with other carbon-based matter, including living organisms. This research is aimed at investigating a feasible and economical technique for the removal of cyanide from tailing wastewater of Muteh gold mine. In this research, removal from Muteh factory&apos;s waste water, was achieved at Tarbiat Modares University&apos;s mineral processing laboratory through the oxidation of cyanide by calcium hypochlorite. Cyanide oxidizes and changes to cyanide (CNO-) which is 1000 times less environmentally hazards than cyanide. Cyanide titration was accomplished using Rhodanine solution and silver Nitrate. Cyanide concentration in the wastewater, was 270 mg/L. Cyanide removal was achieved at an optimum pH of 12.3. However, at higher temperatures, cyanide removal was complete at this pH level. Optimum Dosage for complete removal of cyanide using calcium hypochlorite was 1.43g/L.

Jan 1, 2005

By G. Van Weert, J. F. Breedveld

Both regular and Silver Impregnated Activated Carbon (SIAC) were studied for their effectiveness in removing WAD (Weak Acid Dissociated) cyanides from solutions at pH = 10. SIAC has already been shown to be effective in the removal of free cyanide down to 30 ppb or less. The present work deals with complexed cyanides. Zinc cyanide was used to represent the WAD component. At pH=10, in either batch or column tests it was not possible to lower the total cyanide in solution from either 30 or 8 ppm to less than 1 ppm, using SIAC, regular activated carbon as received, or after grinding. Silver (metal) impregnation of the carbon was not beneficial in the removal of WAD cyanide. However, when silver is added as silver ions (nitrate), the cyanide is adsorbed as silver cyanide in preference to zinc cyanide. The latter compound converts to zinc (hydr) oxide. This way, the cyanide concentration in solution can be lowered below 1 ppm, even when zinc cyanide is already adsorbed on the carbon used. A single exploratory test with added copper ions indicated a similar effect for that system.

Jan 1, 2004

By Charles H. Buclmam

"Environmental regulatory requirements for discharge of solutions and closure of operations for the gold mineral processing industry have been gradually lowered and in certain instances have been targeted to USEP A inorganic drinking water standards for dissolved ions in solution. The use of jar tests for water treatment process development is suitable for preliminary scoping work to be conducted in the research laboratory, as well as for optimization studies at the site of the treatment requirement. This paper will describe experimental methods which were performed using standard jar test equipment in efforts to produce solutions which meet USEP A inorganic drinking water standards after chemical treatment of cyanide solutions. The materials tested included gold bearing pregnant solutions from heap leaching operations, gold plant barren solutions from the Merrill-Crowe zinc cementation gold recovery process and gold heap leach wash solutions after carbon-in-column gold recovery. Experiments included cyanide destruction with sodium hypochlorite and arsenic and selenium co-precipitation coupled with mercury precipitation.IntroductionCyanide leaching solutions are used to selectively dissolve metallic gold from commercially viable mineral deposits. The heap leaching process involves stacking of gold bearing ores on specially designed solution containment pads and percolating alkaline cyanide solutions through the ore to dissolve the gold. Pregnant solutions containing the dissolved gold are collected and sent through a gold recovery process. After selective recovery of the gold, the barren solutions are recycled to the gold extraction process after adjustment of the solution alkalinity and available cyanide concentrations."

Jan 1, 1997

By K. R. Coulter

"Good morning gentlemen. I am very pleased to have this opportunity to tell you a few of the things that happen within a completely unrelated activity, the electroplating industry, except that it does consume metals and has some slight similarity of problems so far as cyanide is concerned.First, just a few general terms about the industry. It is a relatively unsophisticated industry technically, and in many instances there are serious problems in obtaining staff that can operate the various systems that are currently available for destroying cyanide or precipitating metals.I would suggest to you that if you are investigating any system that you consider very seriously the personnel that are actually going to run it. The installation people; probably have some idea what it is all about but the operators must be chosen for their ability and not because they just happen to be available.We perhaps have another area in common. There is very little money for capital expenditures that produce no immediate return or even eventual return on the investment.The industry is largely made up of ""Jobbers"" who are strictly electroplating. There is another group in which the electroplating is captive as in large companions where it is a convenience operation. Also there are specialists, who do other things besides plating but it is a very major part of their operation. This applies to the automotive parts industry.Cyanide applications in the plating industry will be for copper, zinc, cadmium, silver, brass, and gold. Cyanide waste solutions come from those solutions adhering to the plated parts, and from the occasional discharge of the plating bath solutions. Also, in a related industry, the heat treating people with cyanide case hardening have some high concentrations of cyanide to dispose of. Concentrations of cyanide that we treat are 2500 parts per million or higher especially in wastes from heat treating. Solution volumes might be as low as 100 gallons per hour in a well run, carefully operated rinsing system. It may be as high as 3000 gallons per hour where dilution occurs."

Jan 1, 1973

By A. G. Roach

IT IS generally stated that the gold ores of Nova Scotia are free-milling, and for the most part this is true. However, there is a certain proportion of the gold finely disseminated throughout the sulphides, notably arsenopyrite, and this gold is definitely not recoverable as &apos;free-milling&apos; gold by amalgamation. The proportion of free-milling gold to total gold seems to vary widely in different localities in the Province and is lowest in deposits of the fissure-vein type. The problem of recovery of these relatively recalcitrant values is usually one of economics, in some plac.es a simple gravity concentrate being of such low tenor that its extraction and subsequent disposal will not bear the costs involved. In other cases, such a high percentage of values escapes from the mortars and plates that concentration is definitely indicated. The size of the mining operation is also an important factor. In the large majority of cases, however, some concentrating step is warranted, even if the resulting concentrate is stock-piled until sufficient has accumulated to justify further treatment.

Jan 1, 1940

By F. W. De Vries

A review as of the date of this meeting will cover the writer's perception of eachof the areas indicated in the charts. Changes in many are occurring with enough frequency that a detailed summary would be inaccurate within a few days of writing; for this reason, only an outline is appropriate for advanced preparation.

Jan 1, 1998

By JIAQI JIN, Joe Milbourne, Maoming Fan

Gold is very important to support the financial system, and to be used in industries of the jewelry, high-tech fields such as electronics and aerospace, etc. Gold is mainly extracted from three types of ores: primary ore (vein gold), placer (alluvial gold) and associated ore. Cyanide was widely used in gold ore flotation to depress gangue minerals and leaching/cyanidation. The process of extracting gold from gold ore, its separation and flotation concentrate, specifically through a technique called cyanidation or cyanide leaching. This method, which has been dominant since the 1970s, utilizes a dilute solution of cyanide to dissolve gold from the ore. While effective, the use of cyanide raises environmental and safety concerns due to its high toxicity. Cyanide spills can have severe environmental consequences. This has led to the exploration of alternative, environmentally friendly reagents. This paper discusses processing results using the alternative flotation depressants such as sodium sulfite (Na2SO3), etc. to produce a goldrich flotation concentrate for sale to a smelter or as feed to an alternative leaching agent. and methods to extract gold from ore without relying on cyanide.

Feb 22, 2026

By Roger L. Beals, George A. Tweedy

I. INTRODUCTION. THE results of the cyanide-operations, given in detail in the following paper, show the progress that is being made at the Minas del Tajo. The old pan-amalgamation process, in operation up to and including 1905, while paying a profit on high-grade ores, was no longer able to treat profitably the ores in sight at that time, hence an alteration in the process was imperative. The success of this alteration is eloquently expressed by the following data Pan- Amalgamation. Cyanidation. 1905. 1907. 1903. Tons treated, . . 51,387 53,983 69,300 Value per ton (U. S. currency),. $10.75 $8.39 $8.28 Extraction, per cent., 65.00 88.50 S7.45 Extraction, per ton. .- $7.00 $7.4.; $7.24 Total cost, per ton treated, 6.50 4.311 4.01 Profit, per ton treated, . . 0.50 3.07 3.23.;

Feb 1, 1910

By Courtney A. Young

Cyanide is a fast-acting, highly toxic substance but, at the same time, is deemed essential for sustaining life as well &apos;as our standard of living. In this manuscript, the facts about cyanide are presented beginning with a brief history and definition and ending with a discussion on cyanide alternatives. Other topics include speciation, physical characteristics, toxicity, manufacturing, cyanogenics, cyanide cycle, separation, destruction, and markets including those outside the mining industry. Emphasis, of course, is placed on gold production by leaching and how it is influenced by ore type, mineral characteristics and economics as well as its advantages and disadvantages.

Jan 1, 1998

By C. G. McLachlan

Abstract This paper deals with the application of the cyanide process to recover gold from a pyrite concentrate produced by means of differential flotation. This concentrate before cyanidation contains from 0.09 oz. to 0.14 oz. gold per ton, of which only about 60 per cent is recoverable. The rest is so fine that it remains interlocked in the pyrite and therefore is not acted on by the cyanide. The concentrate also contains about 15 per cent pyrrhotite and 0.4 per cent chalcopyrite, both of which are cyanicides. The cyanicidal effect of the pyrrhotite is inhibited by preacracing the pulp with lime, and maintaining a high lime alkalinity during cyanidation. The effect of the chalcopyrice is reduced as far as possible by removing those particles which are free by means of a further flotation step immediately prior to cyanidation. This involves the flotation of some very fine material. After nullifying as far as possible these two cyanicides, the concentrate is cyanided directly, i.e., without being roasted. This leaves the pyrite available for subsequent sale as a source of sulphur dioxide and sulphuric acid, and the entire residue of the cyamde plant, amounting to about 500 tons per day, 1s now being disposed of in this way. Prior to deciding on direct cyanidation, a number of laboratory roasting tests were made. These showed chat, 1f proper control were exercised, a better recovery of gold could be effected from the roasted product than by the direct method of treatment. The tests also showed that the capital cost o the plant would be much higher than that needed for the procedure adopted. The possibility of subsequently selling the pyrite for its sulphur content would also have been eliminated. Introduction A previous paper has described in considerable detail the application of the flotation process to improve gold recovery from Noranda&apos;s milling ore, and in so doing has covered the production of an auriferous pyrite concentrate. The present paper deals with the recovery of gold by cyanidation from that concentrate. This gold, though intimately associated with the pyrite, can, for metallurgical purposes, be considered as all occuring in the native state.

Jan 1, 1946