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By Peter Mason, Chris Walker, Mike Costello

The Phase I electrowinning system at KCGM's Fimiston Operation utilised the well proven technology of electrowinning precious metal values onto steel wool followed by calcining and direct smelting to bullion. The above process, while reliable and successful, was to some extent labour intensive. The Williams Mine in Ontario, Canada had published conditions under which precious metal values are electrowon onto woven stainless steel and directly removed using high pressure sprays. The current paper describes the testwork which was carried out to check the applicability of the Williams criteria to KCGM eluates arising from the elution of highly loaded carbon from the calcine circuit and lowly loaded carbon from the float tails circuit. Information is also given on the commissioning and opera­tional experience which occurred.

Jan 1, 1996

By Norbert Steiner, Roy Norcross

For the desulfurization of weak SO2 gas streams, Degussa developed a process using dilute H2SO4 solution containing H2O2 instead of conventional gas scrubbing with all solid absorbent medium (limestone, MgO). The process is based on fast reaction of H2O2 with SO2 yielding H2SO4 up to 70% strength, depending on off-gas tem­perature. Compared to the conventional systems with typically < 95% efficiency, independent on the raw gas SO2 concentra­tion, residual SO2 concentrations of less than 20 mg!Nm3 can be easily achieved, corresponding to nearly 100% removal. These features render the H2O2 process a very attractive, low capital cost technology to retrofit existing conventional desulfurization plants.

Jan 1, 1996

By Richard Ladyman, Ken Baxter, G. B. Siddall

The IPS process, developed by Baxter and McAuley, was first applied in Australia in 1984 at Browns Creek in NSW where a small 300kg batch plant was in operation for a number of years. To date a further 14 plants have been installed. While a number of engineering companies have engineered applications of the technology, a majority of the plants constructed to date have been constructed by Como Engineers who have a reference list of 9 installations with batch capacities up to 3.0 t.

Jan 1, 1996

By G. A. Hayes

The range of gold ores tested at AMMTEC LTD over several years has resulted in the requirement to analyse for the mode of occurrence of gold in order to assist selection of ore processing options. The aim of this paper is to describe the laboratory testwork and analytical procedures which have been of benefit in detail­ing the mode of occurrence and mineral associations of gold and hence being of value in developing an optimised ore processing route. The range of ore and mineral assemblages described include relatively simple pyrite and free milling ores, more complex pyrite plus arsenopyrite gold ores and the quite com­plex associations of gold in copper bearing ores or with car­bonaceous mixed sulphide ore assemblages. The aim of this paper is to describe the laboratory testwork and analytical procedures which have been of benefit in detail­ing the mode of occurrence and mineral associations of gold and hence being of value in developing an optimised ore processing route. The range of ore and mineral assemblages described include relatively simple pyrite and free milling ores, more complex pyrite plus arsenopyrite gold ores and the quite com­plex associations of gold in copper bearing ores or with car­bonaceous mixed sulphide ore assemblages.

Jan 1, 1996

By Shawn Healey

The Mineral Hill Mine, owned and operated by TVX Gold Inc., is located in the Beartooth Mountains, 5 miles north of Gardiner Montana, U.S.A., which is the north entrance of Yellowstone National Park. Mining is carried out underground using ramp attack cut and fill as well as room and pillar mining. The mine currently employs approximately 145 people and is producing 550 tons per day at a grade of around .21 oz/ton.

Jan 1, 1996

By E. J. Rogans, W. N. Cartner

Carbon technology has largely superseded filtration plants as the more acceptable gold recovery technology. This has, over the last two decades, provided a tremendous driving force for the development of new equipment. One of the main focus areas of this technological development is the development of effi­cient interstage screening systems. Several variations of exter­nal and internal screens are available, with the more recent shift away from air cleaned units to mechanically swept units. This paper discusses the development of one such mechanically swept interstage screen and how the development led to the suc­cessful implementation of a carousel type of CIP operation. The first generation Pump-cell emerged as a consequence of the success achieved with the mechanically swept NKM screen, The idea was to modify the screen to incorporate the functions of pumping, screening and agitation in a single drive unit, the screen generating sufficient lift for interstage slurry flow so that all contactors would be at the same level. This sys­tem was further incorporated as a high intensity modular CIP contactor, i.e. low slurry residence times combined with high carbon concentrations. A discussion on the kinetic gold adsorp­tion theory and its manipulation in the design of the pump-cell concept is discussed in a paper published in a previous Randol Conference< 1), Testwork carried out at Vaal Reefs proved the concept of the Pump-cell on a pilot plant scale<2), which resulted in the building in 1990 of the first large Pump-cell plant at West Witwatersrand Gold Mine designed to treat 340m3 of pulp per hour and , even though the plant operated successfully with respect to gold recovery performance, a few problems were experienced with the basic engineering design(3),

Jan 1, 1996

By Douglas R. Shaw

The results are discussed herein of laboratory and pilot scale research which has demonstrated some exciting prospects for the exploitation of refractory gold resources by heap leaching. The research examined practical and cost effective methods of chemical; i.e., non-biological, oxidation pretreatment of refrac­ tory old ores to enable successful conventional cyanide heap leachmg. The work has focused on regenerable chemicals, in order to minimize process consumable costs. A nitric acid method has emerged which offers rapid oxidation rates (eg, 0.5 to 6 hours) on ore samples crushed typically to% to ¾-inch. Gold recoveries in simulated heap leaching tests, after nitric acid oxidation of crushed ores, were as high as approximately 80 to over 90%, in contrast, typically, to negligible gold solu­bilities without oxidation. Nitric acid oxidation was effective when applied to several sulfide-bearing refractory gold ores which required either partial or essentially complete sulfide sul­fur conversion for high gold solubilities in cyanide. Ores rich in organic preg-robbing matter also were treated successfully, as were ores which contain significant quantities of acid-consum­ing constituents. Base metals also were recovered with nitric acid oxidation from some of the ores which contain these ele­ments. The work related oxidation and solution diffusion behav­iors and the important physical, textural, and mineralogical characteristics of the different ore types. Conceptual-level feasi­bility studies have defined the principal capital and operating cost components of the nitric acid method, sufficient to allow reliable comparisons with other oxidative technologies.

Jan 1, 1996

By Norbert Patzelt, Johann Knecht

Future ore reserves of major gold producers in North America and elsewhere will consist of refractory gold ores. About 60 % of the current U.S. gold production is mined in Nevada. Several of the large gold operations in this state indicate that 40 to 90 % of their future ore feeds will contain refractory gold. To com­pound problems, average head grades for refractory U.S. gold ores had fallen from 8 - 9 g/mt to about 4 g/mt by 1991. In Latin America, 52 % of the gold operations will require milling for optimal recovery. Deeper reserves are, like in North America, refractory. Therefore a special treatment process is needed in order to allow for the gold ore to be leached downstream in a conven­tional cyanidation process for a high gold recovery. There are several options available for this oxidation process like treat­ment of the gold bearing ore in pressure oxidation, in a biooxi­dation or in a roasting plant depending on the reason for the refractoriness. If organic carbonaceous matters and sulfides are the prima­ry reasons for the refractoriness, whole ore roasting is a pre­ferred method for the treatment of this type of ore. Since dry ore is to feed to the roaster, a dry grinding mill is advantageous. For the dry grinding system, the moisture content and the ore char­acteristic is of importance. Those parameters decide the mode of the grinding system. For autoclave systems common wet grind­ing systems can be applied. This paper deals with technical aspects for dry grinding plants and gives an outlook on and pos­sibilities for new grinding systems.

Jan 1, 1996

By Eberhard Stolarski, Michael Tacke

When the oxidized surface gold deposits are mined out, the underlying refractory gold ores become the challenge of treat­ment systems. The size and value ofrefractory gold ore reserves are a function of recovery efficiency and operating cost. The start-up of LURGI's gold roasters at NEWMONT's Carlin site has established whole ore gold roasters as a key to high gold recoveries. The ores from several deposits of the Carlin trend are roast­ed utilizing LURGI / NEWMONT technology, which has achieved gold recoveries approaching 95%. This is in dramatic contrast to the traditional perception that roasting is limited to gold recoveries in the mid 80's. Extensive investigation in pilot scale is required to achieve stable high gold recoveries for most variables in the ore body. The key question for all pilot tests is the classic question of (ROM) run of mine ore roasting or concentrate roasting. All variables are dominated by the leaching/ recovery char­acteristics of the natural ores. The degree ofrecovery improve­ment by roasting / calcining establishes the frame of the eco­nomical conditions. The full range of flexibility is required for the design of the plant to allow for ore variations in heat values, combustible con­tents, agglomeration behavior and off-gas composition. The variables in the ore body influence, therefore, the price of the plant proportionally to its flexibility. Concentrates are usually fairly stable in composition, com­bustion behavior, heat values and particle size since they are a product of the very selective flotation process. Flotation is not the successful process step when the tailings remain high in refractory gold contents.

Jan 1, 1996

By Gregory Owen Lewis, Mark William Johns

The use of resin-in-pulp (RIP) to recover dissolved metal ions from slurries is receiving increasing attention. A number of engineering aspects have been identified as crucial if a RIP sys­tem is to operate efficiently. These are the mixing of the resin and pulp, the transportation of the resin and pulp and the sepa­ration of the resin from the pulp medium. Evaluation of numer­ous alternatives revealed that air agitation is the most suitable means of mixing to effect uniform distribution of the adsorbent and to effect a high mass transfer rate, airlift pumps are the most effective method of transporting the slurry particularly as they are characterized by a low degree of resin degradation and sieve bends are the most suited means of effecting the resin/pulp sep­aration. This paper details the design of the reactor that incorporates the three identified unit operations and presents data obtained from the contactor when operated at a throughput of I 00 000 t/m. The airlift pump was found to be sensitive to pulp density and submergence ratio. The screening ability of the sieve bend was influenced by resin and the pulp density . The reactor is a cost effective, metallurgically efficient unit for the recovery of metal ions from high density slurries.

Jan 1, 1996

By Lech Bolinski, Joe Shirley

Over two dozen Resin-in-Pulp (RIP) plants have been in operation in the fonner Soviet Union since the beginning of 1970. Currently approximately 50% of the gold produced in Russia, Uzbekistan and Kazakhstan, which equates roughly to 10% of the total world output, is recovered using the RIP technology. An alternative to activated carbon, ion-exchange resin has several advantages for the recovery of gold. Resins are less prone to clay or organic foul­ing and do not require thennal regeneration. They also have poten­tially higher loading capacities, faster adsorption kinetics, and are more resistant to abrasion. The original Russian RIP process was based on engineering expertise developed for uranium ore pro­cessing and has a few major drawbacks. The biggest problem is an 18-30 day resin stripping process, which results in a huge gold lock-up. The problem was recently overcome by the development of a new stripping technology which cuts the time to 12-24 hours. Currently, there is rather limited practical knowledge of the Russian RIP process in the West, but often Western mining com­panies developing gold mines in the fonner Soviet Union are hard pressed by their local joint venture partners to take a serious look into RIP. It is probably only a matter of time before one of these companies will cross Soviet technology with Western engineering and develop a modem RIP process as an attractive option to the current CIP and CIL technologies.

Jan 1, 1996

By Richard M. Crowell, John W. Shield

GeoBiotics has developed a biooxidation technology (patents pending) which involves coating refractory precious metal sulfide concentrates onto a support material and biooxidizing the sulfides in a heap configuration. The concentrates are produced from low or high grade sulfidic refractory ores or existing mine tailings. The process has been found to achieve high gold recoveries asso­ciated with stirred tank biooxidation, but at the low operating and capital costs associated with whole ore heap biooxidation. Improved gold recoveries of up to 98% after biooxidation are reported for 4 representative mines or deposits. The sulfide flotation concentrates were studied using 3 and 6 in. diameter columns or 3 in. drained vats. The refractory sulfide concen­trates biooxidize rapidly in 3 to 12 weeks with substantial increases in subsequent gold recovery.

Jan 1, 1996

By G. A. Plakhin, A. V. Luganov, V. A. Luganov, G. V. Gorbatenko

In order to extract gold from the complex sulphur-arsenic bear­ing raw materials and to remove arsenic and sulphur from the process in an ecologically safe form we have studied oxidizing roasting of highly arsenic gold bearing concentrates with soda, leaching of cinders, processing of the obtained solution and extraction of gold from the cake. There were processed concen­trates containing from 5 to 28% of arsenic, 12-20% of sulphur in the form of pyrite and arsenopyrite. The content of gold in the concentrates was 4-75 git. The roasting temperature was changed in the range of 773-l 173K, the consumption of calcined soda was 75-200% of stoichiometric necessarily for bonding of arsenic and sulphur into the water soluble compounds, the dura­tion of the process was varied in the range of 10-120 minutes. Under roasting in optimal conditions up to 97% of arsenic and 95% of sulphur go into water soluble compounds. The out­put of cake is 65-70% of the concentrates. The extraction of gold from the cake is higher than from the raw concentrates. The technology has been tested on a pilot plant scale

Jan 1, 1996

By Brad Hewitt

Since Campbell Mine began processing ore, there has been a gravity gold recovery circuit. From 1947 to 1982, gravity gold was concentrated through the combination of jigs and mercury amalgamation. In 1982, jigs with concentrating table upgrading commenced and was utilized until the end of 1994. As of January of 1995 to the present, Knelson Concentrators in com­bination with concentrating tables have been employed to achieve a refinable product. An evaluation of the justification used for the last change is the focus of this paper.

Jan 1, 1996

By Paul D. Chamberlin

There are many unit operations applicable to the processing of gold/copper ores. Deciding which are most applicable to your ore can be done using a series of tree diagrams. The diagrams show generalizations, not definitive rules. And the listing of process alternatives on the diagrams is very limited although there are dozens to choose from. Three questions help point the way to proper process selec-tion: 1. How much gold is in the ore? 2. How much copper is in the ore? 3, What is the cyanide consumption when leaching the ore?Halogens can also effectively leach gold ores and gold/cop

Jan 1, 1996

By Lawrence Devon Smith

"Within the mining industry the term “due diligence” is used to describe a detailed data review, generally in connection with the purchase or sale of a mineral property, the approval of a large capital expenditure, or the borrowing of a large sum of money.The term originates in the requirement of the board of directors of a corporation to “act honestly and in good faith and exercise the care, diligence, and skill that a reasonably prudent person would exercise in comparable circumstances” (OBCA, 1994). Furthermore, the law assumes that a corporation (or its board) will have exercised due diligence in the acquisition of an asset and, therefore, knowingly (in the absence of fraud or deceit) will have taken on the liabilities and obligations associated with the asset (Nelson, 1994). This is the familiar “Buyer Beware”.Directors are liable for their decisions except “if the director relies in good faith up on financial statements of the corporation represented by an officer of the corporation or in a written report of the auditor, or a report of a lawyer, accountant, engineer, appraiser, or other person whose profession lends credibility to a statement made by any such person.”(OBCA, 1994).Hence the importance of reports prepared by professionals. They provide confirmation that the directors have exercised due diligence in the performance of their duties. For this reason these reports are referred to as due diligence studies."

Jan 1, 1996

By Thomas Havlik

It is proposed to realise the direct leaching, during which will be generated elemental sulfur and not sulfate or sulfuric acid as end product, under conditions that sulfur will not cover the leaching surface and Hot hinder the leaching course. The following improvements have been considered: -use of organic sulfur solvents -ultra high-frequency leaching -ultrasonic leaching -use of surface detergents or surfactants in leaching processes -simultaneously crushing and leaching These proposals are under investigation and preliminary results are promising

Jan 1, 1996

By MattelmSki M

Outokumpu Harjavalta Metals Oy has been producing nickel since 1962, based on conventional flash smelting technology followed by electrowinning of nickel. In the 1980s, a research project was initiated to develop a converterless direct smelting process to produce matte for further refining in the then existing refinery. The process was tested on a pilot plant scale at Outokumpu&apos;s research centre in Pori and was found to be viable. The process was named the Direct Outokumpu Nickel Smelting Process or the DON Process. At the turn of the 1990s, Outokumpu studied various options to develop its nickel business and the Harjavalta operations. As a result of this work, the DON Process was further developed to produce two mattes: low iron matte in the flash furnace to be leached in the existing leaching circuit and high iron matte in the electric furnace to be leached in the new leaching circuit. In Harjavalta&apos;s case, it was essential and important that the process could use the existing flash furnace and electric furnace without converters.

Jan 1, 1996

By Darrell M. Hladun, Linda M. Dufour

The benefits of computer simulation in the design of a refracto­ry gold autoclave facility is discussed. Three computer simula­tion programs used for autoclave design are briefly described in this paper. 1) METS IM® - A Process Simulation Software Package Developed by Proware: Mass and energy balances are conducted around the auto­clave and its ancillary processes. Results from the process simulation define process equipment requirements and are used for establishing operating costs. The p_rocess model integrates various unit operations including grinding, acidu­lation, pressure oxidation, counter-current-decantation, neutralization, cyanide leaching, and carbon-in-pulp or car­bon-in-leach. 2) ALGOR® - Finite Element Analysis (FEA): A computer software program is used in the design and analysis of brick lined pressure vessels, such as autoclave, heater, and flash vessels. This software creates a steady state thermal model, and accurately predicts temperature distribution throughout the entire vessel, including nozzles, which represent regions of high thermal intensity. 3) Compress©: A software package developed by Codeware used for the sizing of pressure vessel components, includ­ing shells, heads and nozzles, according to ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.

Jan 1, 1996

By A. Goulsbral, D. Harrison, R. Dunne

A programme to reduce cyanide consumption at the New Celebration Gold Mine, situated 32kms South of Kalgoorlie, Western Australia, commenced in the latter part of 1990. Cyanide speciation studies at the time identified that the major loss and consequently consumption was due to the hydrolysis of cyanide, The use of artesian hypersaline waters of high magne­sium content on gold plants in Western Australian Goldfields has meant that economically viable operating pH values during cyanide leaching are around 8.9 to 9.5. The high ionic strength in these waters does to some degree retard the hydrolysis reac­tion. Notwithstanding this, the formation of hydrogen cyanide and its loss due to volatilisation is the cause of the major loss of cyanide on most gold plants in the Kalgoorlie Goldfields. This paper discusses the aspect of oxygen addition during cyanide leaching to decrease cyanide consumption and increase gold recovery.

Jan 1, 1996