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By Michael N. Allenby

One of the least discussed areas in the ever-improving technologies of gold recovery from ore bodies and tailings is the chemistry of the waters used in the plants. Carbon-in­ pulp, carbon-in-leach, heap/dump leaching and iological oxidation processes are all affected by water quality. The remoteness of a lot of the plants means that the large water requirements can often only be met by a ground water source. The chemistry of waters from different sources poses different problems, but generally a lot of these waters are scale forming. Scale-forming tendencies can be described by calcium, magnesium, barium and strontium assays. They can be notated by Langelier and Ryznar indices. They can be plotted by computer programmes that print out scaling indices at different conditions. The propensity to scale can -be readily determined. The prevention of scaling -or at worst minimisation of scaling -is the ambition of the suppliers of scale inhibition programmes. This prevention/minimisation technology is discussed below.

Jan 1, 1993

By Harry M. Castrantas, James L. Manganaro, Craig W. Rautiola, James Carmichael

Caro's acid (peroxymonosulfuric acid) was successfully field tested as a cyanide detoxification agent at a North American gold mine. An on-site FMC generator injected Caro's acid into a mill tailings slurry sump. The WAD cN-(weakly acid dissociable plus free cN-) was reduced from 40-108 ppm to below the target level of 20 ppm using a 1/1 mole ratio of CA (Caro's acid) /CN-. At an inlet CA/CN-mole ratio of 1.8/1, WAD CN­concentrations as low as 4 ppm cN-were achieved. Raw material costs for the cyanide detoxification were cut by 60% compared to using hydrogen peroxide (H202) alone. Detoxification time with Caro's acid was much faster compared to H202. This resulted in completion of detoxification before the treated slurry reached the tailings pond thereby substantially reducing the probability of wildlife fatalities.

Jan 1, 1993

By A. L. Putz, G. Ladouceur, A. R. Laplante

A laboratory centrifugal concentrator was used to evaluate two gravity circuit configurations treating a flash flotation concentrate at a Canadian gold mill. The Initial circuit consisted of a 76 cm (30 Inch) plant Knelson Concentrator (PKC) for coarse gold removal. Later, a hydroseparator and spiral were Installed, with the hydroseparator underflow feeding the spiral and the spiral tailings plus hydroseparator overfiow reporting to a 51 cm (20 Inch) PKC. Gold recovery In the 76 cm PKC averaged 45%. Gold was recovered consistently In all size fractions greater than 38 µm, where recovery dropped to 22% for the -38 µm material. Changing the circuit to Include the hydroseparator and spiral decreased the Knelson unit recovery to less than 17%. The decrease was attributed to the spiral which recovered much of the free gold ahead of the Knelson and to changes In the mill feed (free gold portions were finer and less abundant). The spiral demonstrated erratic behaviour although It still recovered significant coarse gold (+75 µm) yielding unit recoveries of 18-44%. Although mechanical difficulties were experienced with the 76 cm PKC, Its performance was superior to that of the hydroseparator, spiral and 51 cm PKC configuration. Much of the gold In the ball mill recirculating load was found to be too coarse for significant recovery In the flash flotation cell and should be recovered by gravity from the cyclone underflow or ball mill discharge. The LKC proved to be a successful device to evaluate gravity recoverable gold content. Dilution of test samples with silica further enhanced this methodology.

Jan 1, 1993

By Joseph A. Dos Santos

Developed in 1983, High Angle Conveyors HAc®s, are proven versatile systems for elevating materials continuously from a lower to an upper level, Such systems may also be used to lower materials continuously. HACs have found commercial application in widely varying materials ( including coal, refuse, coarse ores, hot clinker, municipal sludge, wood chips, gypsum, slag, excavated earth, various grains and RDF), at widely varying throughput rates from 0.27 to 4,000 t/h. The conveying profiles have varied widely and elevating heights range from 3.66 m to 175 m. HACs have found application in coal, copper, gypsum and gold mining, coal preparation, in municipal waste treatment, rapid transit projects, pulp and paper mills, and cement plants, While noting a wide variety of applications in general, the present writing focuses on a very large HAG® system, consisting of eight (8) main HAG units to elevate nickel/copper ore continuously from under­ground, 1402 m (4600 ft,) vertically to the surface. It compares technical and economic aspects of such a system against traditional mine hoist haulage,

Jan 1, 1993

By Marlin D. Schutte, Graham M. Fraser, Paul M. Kubera, Ronald J. Weetman

Mixers play an important function in the operation of multi-phase reactors in the minerals processing industry. They must suspend solids, transfer oxygen, maintain pH and temperature uniformity, assist in heat transfer, and, in biological processes, avoid the development of excessive shear rates. The LIGHTNIN A315 impeller (Figure 1) effectively supersedes the older Rushton turbine (Figure 2) which has been classically employed in gas­Iiquid-solids applications such as bacterial oxidation, cyanide destruction, etc. Since a stirred tank reactor can be such a key part of the overall process, it is essential that the mixers be designed for long term reliable operation, both process and mechanical, to insure a high percentage of on-line availability. Mixers in gas-liquid-solids processes may experience extraordinary loading conditions which must be taken into account to guarantee a robust mechanical design. Given the recent trend towards the design of world-class process units with maximum capacity equipment, there is increased importance and emphasis on the integrated design of the complete agitation system -mixer, vessel, and structure -to insure trouble free, post­commissioning performance. This paper presents some of the considerations necessary to specify the process functions of the mixer in multiphase applications, as well as special considerations for the mechanical design of the integrated reactor system.

Jan 1, 1993

By Harry Holle, Ivan Hunter, Darrin Thomson, Gary Johnson

Over the past five years Dominion Mining Limited has directed an on-going effort towards optimising the performance of its milling circuits. The approach has been on a wide front, and has addressed a variety of issues associated with the design and operation of SAG milling circuits. Major projects have been conducted in the areas of flowsheet optimisation, mill liner efficiency, and dynamic circuit performance. As a result the initial designs of many of the Dominion circuits have been modified, mill liner specifications have been rationalised, and a robust automatic control system has been developed. A group-wide approach was taken on most of these projects, resulting in substantial benefits to both the individual operations and the company as a whole. By applying the projects group-wide a significant multiplier effect has been gained on the funds invested in each project. Extensive use of steady state modelling techniques has been made in order to understand the performance of the different circuits, and to highlight the potential areas in which improvements can be made. Liner optimisation has been primarily aimed at achieving predicability of performance, both metallurgical and mechanical. The development of a robust automatic control system has enabled the dynamics of the milling process to be controlled, and resulted in an additional increment in throughput being achieved. The combined effect of these efforts has been to raise plant availability to consistently over 95% (on a long term basis), to improve the power efficiency of comminution (in SAG mills) by 20% or more, and to enhance the dynamic performance such that a more than 10% increase circuit throughput has been demonstrated.

Jan 1, 1993

By Chris Cox, David Green

Outokumpu has developed the HG or High Grade flotation cell over the past decade. This machine gives upgrading and selectivity performance superior to conventional mechanical cells while maintaining their simplicity, ease of operation and recovery characteristics. The HG design is available in a tank cell configuration which provides a number of benefits in plant design and operation. This paper will describe the HG Tank Cell and the "Virtual Column" concept. Results are given from the operation of the HG Tank Cells at Lac Minerals - Est Malartic in Quebec, Canada. Further discussion of applications for gold recovery is also provided.

Jan 1, 1993

By Peter J. Lawson, John A. Rideout, Gregory W. Dicinoski

A considerable body of literature directed towards optimising the efficiency of gold and silver extraction from cyanide leach liquors has appeared in recent years. A few examples from dissolution to solvent extraction to adsorption in carbon-in-pulp (CIP) and resin-in-pulp (RIP) operations follow. Selective leaching of gold from copper-gold ores using ammonia-cyanide mixtures extends the % copper which may be tolerated in ores (Ruane, 1991, LaBrooy et al., 1991, Costello, 1991). The removal of copper and recycling of cyanide from high copper ores is another important development (Sceresini and Staunton, 1991). Solvent extraction of alkaline cyanide liquors (Riveros, 1990, Mooiman & Miller, 1991) and solvent aided elution in CIP (Muir, et al., 1985) look promising. Recent definitive papers on the mechanism of adsorption of aurocyanide by activated carbon should lead to more efficient use of CIP (Adams and Fleming, 1989, Klauber, 1991). Strong and mixed weak-strong base resins have been applied in RIP for aurocyanide extraction in Russian Plants since the 1970's (see for example Borovskii et al., 1985, and references cited in Fleming, 1988a). Fundamental studies on applications of commercial weak and strong base resins-in-pulp (Fleming & Cromberge, 1984a, b, Fleming 1988a, Hosking 1984, Riveros and Cooper 1987) have generated much interest in RIP. Detailed comparisons of CIP vs RIP efficiencies at Mintek in South Africa (Fleming et al., 1988b), and the inefficiency of CIP in contact with clay led to the commissioning of the strong base RIP Golden Jubilee plant in 1988. Its operation and improvements have been reported (Seymore and Fleming, 1989, Fleming & Seymore, 1990). The use of anion exchange membranes for aurocyanide extraction shows some promise (Mauthoor et al., 1991). However, the development of new gold specific resins at Mintek (Green et al., 1984, 1986, 1990, Johns and Green, 1991) and elsewhere (Asker et al., 1987, Wilson et al., 1987, Harris et al., 1992) should improve the viability of RIP processes. The polydiallylamine gold specific resins (Hodgkin & Eibl, 1988, Fawell et al., 1992a, b) have high capacities for auro cyanide recovery from high concentration liquors. The use of guanidine based liquid and solid ion exchange extractants for gold was recently reported by the Henkel Corporation (Kordosky., et. al., 1993). Such specific resins tailor made for gold and/or silver cyanide extraction should lower overall cost by improving metallurgical efficiency. In the case of strong base resins this selectivity largely eliminates the problems of poor base metal elution and/or poisoning. The work reported here outlines the approach taken at the University of Central Queensland to synthesize sterically hindered strong base anion exchange resins which are designed to have high selectivity for auro- and argentocyanide complexes. It summarises selectivity tests on low grade cyanide leach liquors from several mines. It also examines an RIP vs CIP comparison, and investigates the elution properties and cycling of one such promising resin.

Jan 1, 1993

By C. J. Ferron

Gold occurrence in operating plant tailings ranges from gold in solution, fine free gold, gold associated with sulphides/arsenides/tellurides and gold occluded within iron oxides or arsenates and silica gangue. This paper briefly presents various alternatives to reprocess gold tailings, with examples. These include the use of centrifugal gravity separators, CIL, magnetic separation, flotation and pressure oxidation.

Jan 1, 1993

By R. R. Pierce, C. E. Semler, K. G. Thomas, R. A. Williams, H. J. . H. Pieterse

This paper highlights the experience and knowledge gained at Barrick Goldstrike Mines Inc. with reference to the pressure oxidation circuit. Particular attention is given to the different linings employed on the autoclaves, flash and condenser vessels. Experience gained during the three years of operation is given. A test program and results are discussed. Quality assurance is highlighted. Barrick Goldstrike is 100% owned by American Barrick Resources Corporation, Toronto, Ontario, Canada.

Jan 1, 1993

By Kathleen A. Altman, Kevin Hegerle

FMC Gold Company start.ea processing ore at their Paradise Peak Mine in 1986. Gold, silver and mercury haye been produced from the Merrill-Crowe milling circuit and from heap leaching. There are three heap leach circuits, Paradise Peak, Ketchup Flat and County Line. The Paradise Peak and Ketchup Flat heap effluent solutions are routed into the zinc precipitation plant which is associated with the mill for recovery of the precious metals. The County Lne hea lech circuit is a stand-alone operation, again with a zinc precipitation recovery circuit. The mill was shut down in May, 1993 due to depletion of ore reserves with the remainder of the heap leach ore due to be placed on the leach pads by late summer of the same year.

Jan 1, 1993

By Charles A. Horne

Grinding mill circuits used for particle size reduction of mineral ores commonly use cyclones as primary classifiers. Typically, several individual cyclones are installed in a cluster (Fig. 1) where they can easily be added or valved-out of operation in order to balance classifier capacity with fluctuations in tonnage and recirculating loads as ore grades and hardness vary.

Jan 1, 1993

By Richard W. Jolk

A pollution control equipment exemption which reduces the fair and equitable taxable value of a mine property is allowed under Nevada Revised Statute (NRS) 361.077 and must be filed in accordance with the filing requirements of NRS 361.155. USMX Nevada Operations annually saves a substantial amount of State property tax dollars by taking advantage of this tax exemption. The State documents received by USMX and the documents filed by USMX are reviewed in this paper. The application filed by USMX exhibits the format and detail used to obtain this tax exemption and the extent to which environmental control equipment may be claimed.

Jan 1, 1993

By Johann Knecht

Due to lower specific investment and operating costs the tendency towards large scale equipment will remain. For the design engineers not only the stresses in the mill structure and manufacturing are of importance but also transportation to and erection on site. A scale up of the design of smaller sized units on the pantograph principle may not always give the best approach to the job in this respect. This paper covers recent developments in the design of large size equipment where the huge dimensions call for designs being different to the well known ball and SAG mill concept with cast conical endwalls. The first part describes the features of the biggest ball mill in the world, whereas the second part provides some details of the largest shell supported SAG mills being currently in the manufacturing process.

Jan 1, 1993

By John Wiebmer

Six industry trends will have significant effect on the way mining equipment is designed and supported in the years ahead: 1. MINING IS MIGRATING TO LESSER DEVELOPED PARTS OF THE WORLD The global recession of the early 1980's drove down commodity prices and intensified cost competition. This caused a fairly dramatic trend in mining away from higher cost operations in developed countries to richer, lower cost deposits in developing countries. Miners operating in lesser developed parts of the world will place higher value on rugged, durable designs that can live in more difficult and sometimes abusive conditions. They need engines and power train systems that are more tolerant of a wide variation in fuel quality and oil specifications. They'll require machines that are simpler to operate, simpler to maintain, simpler to troubleshoot and simpler to repair. And they'll require creative means of support in getting technical information, parts and components to remote operational sites. Mining equipment in the future will be more durable and simple than it is today, and product support will grow in importance as purchasing criterion. 2. THE MINING INDUSTRY IS CONSOLIDATING An intense amount of corporate acquisition and industry consolidation activity is occurring, to the point that today just 50 mining companies account for 55% of the western world non-fuel mineral production. Consolidation will continue, leading in the future to an industry structure weighted heavily toward a few key global mining houses.

Jan 1, 1993

By Stanley A. Bunk, Desmond J. Bruyns

The purpose of roasting gold ores is to release for extraction, typically by cyanidation, the small particles of gold which are surrounded by refractory stone. The roasting simply opens up passages for the penetration of solution into the interior of the ore particles. This is accomplished by the removal by volatilization or formation of volatile oxides of certain constituents such as sulfur, arsenic or antimony. Temperature is an important parameter. High temperatures tend to form a dense iron particle rather than a "spongy" calcine. The dense iron particles result in lower gold recoveries. High temperature can cause melting of some components which also results in gold encapsulation. Roasting of refractory gold ore concentrates has been practiced for decades. Multiple hearth, rotary kiln and muffle reactors were first used for roasting. Fluid bed roasting provided a low capital cost, low maintenance technology with better process control and soon became the favored technology. The first fluid bed concentrate roasters were commissioned in the late 1940's. Early fluid beds were "bubbling" type. Environmental considerations did not significantly impact on the design. Feedstocks were highly exothermic and reaction rates were relatively rapid. Roasting today must compete with other technologies for treatment of refractory ores. Ore bodies which are not

Jan 1, 1993

By Hans von Michaelis

The revolution in development of new technology and practices in the gold mining and metallurgy industry continues unabated despite the ups and downs in the gold price. Some of the new cutting edge technologies are listed in Table 1 overleaf. There is room to discuss just a few of these here, but many more are identified and described in RANDOL (1992). Cutting edge advancements in gold recuperation, can be sorted into three categories. The first category includes fundamental advances that offer major improvement with significant economic benefits. Second would include evolutionary developments that offer smaller, but nonetheless commercially valuable improvements. Finally there are those "advances" that are interesting but of trivial or question­able economic benefit to industry. It is essential to adopt a "systems approach" philosophy towards developing and applying new technology. Practical innovation often comes about as a result of having to solve a problem. Innovation for innovation sake is an ego trip. Environmental management has become an important part of the system and the environmental implications of new processes and practices in the mine and mill have to be carefully considered for potential benefits and/or liabilities.

Jan 1, 1993

By Fred Woodcock, A. R. Laplante

A laboratory technique is presented that uses the Knelson Concentrator and a relatively small sample to predict the amenability of a given gold ore to gravity recovery. The technique applies to develop­mental orebodies as well as retrofitting existing plants. Justification for this approach is discussed. Actual results of the technique applied to existing and prospective circuits are presented and discussed.

Jan 1, 1993

By Michael J. Virnig, Keith E. Weerts

The development of heap leach technology for the treatment of low grade gold and silver ores has led to a boom in gold production in the Western United States in the last 15 years. The heap leaching process consists of stacking the mined ore on a specially prepared leach pad followed by leaching with dilute alkaline cyanide solution. Depending on the nature of the ore, it may require crushing and/or agglomeration prior to stacking on the leach pad. As the dilute alkaline cyanide solution migrates down through the stacked ore, the precious metal values along with a portion of the base metal values present in the ore are dissolved to give a pregnant leach solution which is collected at the base of the stacked ore. The precious metal values are then recovered by zinc precipitation or by adsorption on activated carbon. Once all of the economic metal values have been leached from the ore, the spent heap leach pad, the leached materials, and associated process solutions must be decomissioned. Decommissioning requires that the spent heap leach pad along with the leached materials and process solution be treated to reduce the concentration of the residual cyanide, base metal cyanide complexes, and other anionic metal species to levels where they no longer represent a long tenn liability for the environment and the operator. The levels to which these components must be reduced is dependent upon the applicable water quality standards as determined by the responsible federal, state, and local agencies. As environmental awareness has grown, these standards have become increasingly stringent. A number of treatment options have been developed for the de-toxification of the process residues. These include natural degradation which incorporates bio-degradation, fresh water rinsing, alkaline chlorination, hydrogen peroxide, and sulfur dioxide/air. Each of these options has been reviewed with regard to relative effectiveness, generation of hazardous by­products, reagent handling considerations, relative costs, and time requirements by Denton, Iverson, and Gosling I. As an outgrowth of the program to develop Henkel's guanidine based gold extractants, COGNIS, Inc., the environmental ann of Henkel, has developed the CyanoMet R process for the extraction and concentration of the various cyanide and anionic metal species from the dilute aqueous alkaline solutions generated during the process of detoxifying spent heap leach pads. This paper describes the CyanoMet R process, its application to three different feed solutions, and treatment of the concentrate generated by the process.

Jan 1, 1993

By Steve McIntosh

Restoration of a wetland which was initially disturbed at the turn­of-the-century will be undertaken to compensate for the temporary loss of wetlands associated with future mining operations. The proposed mitigation area exhibits xeric conditions as a result of past dredging and gravel mining operations which had the effect of lowering the flood plain surface and wasting the fine surface sediments. Together these mining activities resulted in complete alteration of the surface and subsurface water systems. Water which had inundated the soil profile, now flows on the basalt bedrock, surfacing only for a relatively short time during high flow periods. The conventional approach to wetland restoration in this type of area is to remove surface material in an attempt to bring the surface nearer to the underground water. These operations would require the removal and redistribution of large quantities of gravel, cobbles and boulders and the attendant destruction of existing wetland areas. Rather than lowering the surface elevation to the water level, the mitigation plan conceptualized for this project involves forcing the water to the surface by creating subsurface ponds behind four impermeable barriers. The barriers will extend vertically from the bedrock to the surface. Surface berms will be constructed along the length of each groundwater barrier to enhance sediment deposition and encourage the development of wetland vegetation. This is the least expensive and least invasive method of creating a wetland which will remain saturated to the requisite degree and for the amount of time required for classification as a wetland as defined by the 1989 Federal Manual for Identifying and Delineating Jurisdictional Wetlands.

Jan 1, 1993