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By Donald R. East

For many years there has been increasing pressure on mining companies, not without some justification, to design tailings storage facilities which guarantee some degree of protection against process solutions entering local groundwater and surface water flows. A fairly straightforward approach to achieving this has been to design conventional water-retaining type structures, and this has often been reinforced by the need to store large volumes of process water and seasonal run-off within the tailings facility. The conventional design uses naturally occurring geological barriers and a conventional embankment with possibly a grout curtain, or artificial barriers around the entire facility, using either imported low permeability soils, admixtures, or synthetic liners. While these approaches may achieve the primary objective of minimizing seepage, various other factors should be considered. Firstly, by depositing the tailings slurry in a sub-aqueous manner, the tailings, especially if relatively fine grained, will settle to very low densities and little or no on-going consolidation may occur over the operating life of the mine, There have been many cases where measured pore pressures within the tailings mass equal the total overburden stress, i.e., no consolidation and no strength, many years after decommissioning.

Jan 1, 1998

By Jody Kelso, Thomas R. Clark, Gregory J. Olson

Refractory, sulfidic gold ore from the Metates deposit in Mexico was tested to determine if it could be heap biooxidized to improve gold extraction. Small column tests were conducted in a manner consistent with anticipated process conditions: increased tempera­ture due to oxidation of the high sulfide content ofMetates ore and full recycle application of leach solutions containing high concen­trations of dissolved solids. Biooxidation by thermophilic (heat­loving) microorganisms was tested to determine: 1. the extent of sulfide oxidation and bottle roll precious metal recovery, 2. reagent consumption, and 3. potential solution flow problems due to mineral precipitation.

Jan 1, 1998

By Peter W. Willcocks

The Cyanide Regeneration Process (CRP) was developed by Golconda Engineering and Mining Services and installed at Golconda's Beaconsfield Gold Tailings Retreatment Project situated in Tasmania, Australia. The Tailings Project is a 1000 ton per day carbon-in-pulp treatment plant, feed for which consists of tailings material which is dredged from the Tamar River. The pulp is screened to remove debris, then cycloned to form two products. Underflow pulp is stored in a 350 ton bin and cyclone overflow passes to a thickener. The coarse pulp material is fed to the grinding circuit then rejoins the thickened slimes in the cyanide leach circuit. Gold is extracted by carbon-in-pulp techniques. The plant is sited in rolling, hilly country approximately 200 meters from the Tamar River. The residue disposal area is quite small consisting of four dams, totalling 42 acres. The regional climate is cool and wet with little evaporation; therefore, we anticipated a net increase in contained liquor, and subsequent storage problems. Our plan was to remove cyanide from the liquor prior to returning the detoxified solution to the river system. Such treatment was not required until midway through the second year of the project. Initial testwork on sample material indicated that destruction of cyanide by chlorine was the simple solution. Subsequent follow-up on actual plant liquor indicated a huge chlorine requirement due, we believe, to the substantial degradation of vegetable matter plus organic content from the marine environment. The cost of cyanide destruction could not be justified.

Jan 1, 1998

By Morris Beattie

Arseno Processing Ltd. has developed process technology for the extraction of gold from refractory ores and concentrates. These ores, which do not respond to conventional extraction processes, are rapidly becoming the primary targets for mining companies wishing to become significant gold producers. It has recently been estimated that by the mid 1990's, the annual gold production from the Pacific Basin Epithermal Arc in southeast Asia could be as high as 550 tonnes. Within this area the Porgera deposit under development by Placer, Renison and MIM, and the Lihir Island deposit under development by Kennecott have been shown to be refractory and require pretreatment before the gold can be extracted. The additional deposits which are now starting to be developed in this area are also expected to require such pretreatment. The Arseno process promises to be an economical pretreatment for these ores and to result in the maximum achievable gold recovery. Numerous refractory deposits are also known in Australia, North America, China and other parts of the world. Samples from many deposits throughout the world have been tested using the Arseno process conditions and the consistently successful results have demonstrated its widespread application. The samples which have been tested include ores in which the gold is locked in pyrite, marcasite or arsenopyrite. The process is insensitive to the sulphur content of the feed. Feed materials containing from 1 % to 50% sulphur have been tested successfully with the process. In the Arseno refractory gold process, sulphide minerals are dissolved so that the contained gold becomes accessible for subs7qu7nt gold recovery. This gold recovery is achieved by cyamdat1on of the process residue. For many of the materials which have been tested, gold extractions in excess of 95% have been achieved.

Jan 1, 1998

By P. Ollivier

A comparative study on potential refractory ore processing techniques was launched at the BRGM to enable exploitation of numerous small deposits of arsenopyrite and antimony sulphide ores.

Jan 1, 1998

By Frank J. Skudrzyk, Vladimir F. Petrov

In compliance with the current Russian environmental legis­lation, possible impact of industrial activities on the environment is restricted by acceptable limiting values (maximal allowable concentrations - MAC) of individual chemical substances in the natural environment - water, atmospheric air and soils. These norms have federal status and are valid for the whole territory of Russia. Disposal of the substances, for which no MAC is estab­lished, is forbidden by the law. Many gold mining companies use cyanide in precious metal recovery. This paper overviews the Russian experience in pro­tection of natural water reservoirs from technogenic impact of cyanic technologies. Major toxic compounds, contained in liquid and solid rejects from hydrometallurgical treatment of gold ore using cyanidation, are cyanides (CN), thiocyanates (SCN) and cyanide metal com­plexes. Unlike western classification of various cyanide types, in Russia any inorganic cyanide compounds (simple and in com­plexes with metals), with the exception of iron cyanide com­plexes, are considered toxic and the acceptable limiting value is established for them. MAC is 0.05 mg/I for fish reservoirs and 0.1 mg/I for drinking water. For iron cyanide complexes MAC is 0.15 mg/I for fish reservoirs and 0.25 mg/I for drinking water. Russian norms for thiocyanates are practically as rigid - the acceptable limiting value for them in fish reservoirs is at the level of 0.07mg/l (0.15 mg/I for potassium thiocyanate) and for drinking water - O. lmg/1. Norms for metals are established on the basis of total content regardless of the form in which they are present in water - as cations or complex ions. It should be noted, that in case several toxic compounds of the same limiting value (for cyanides, thiocyanates and base metals the limiting value is toxicological) are present in water. Their allowable concentra­tion is calculated as the sum of actual concentration of each com­pound, divided by the corresponding acceptable limiting value, with the result not to exceed one (compounding effect). Differences in cyanide classification and the necessity to include thiocyanates dictate different analytical methods. This, in a number of cases, results in certain discrepancies in analytical results. Until recently chlorination was used as a basic process of detox­ification of wastewaters. Calcium hypochlorite powder or hypochlorite pulp, prepared of lime milk and chlorine shipped to the plant, were used as a reagent. Chlorination is an efficient method: it allows to completely destroy plain and complex cyanide, in addition to iron complexes, and thiocyanates. A good example of high efficiency chlorination can be found at the Mnogovershinniy mill near the Okhotsk Sea located in the salmon spawning area, for which we designed an automated chlorination plant for tailings dam. Since plant start-up ten years ago, the required concentrations of cyanides and thiocyanates have been kept at the MAC level required by environmental regulatory agen­cies and no harmful affects on ichthyofauna has been reported. One major drawback of chlorination is high cost of the major reagent, as well as secondary contamination of detoxified waters by chlorides. Secondary contamination by chlorides becomes obvious in the course of detoxification of wastewaters of com­plex composition, which require increased reagent consumption. Recent changes in economic conditions in Russia caused the necessity to direct efforts to reduce the costs of precious metals recovery, and in particular, wastewater treatment. We have con­ducted certain work in this direction and obtained positive results. We hope that our experience described below will be of interest to other specialists particularly taking into account the current low gold prices.

Jan 1, 1998

By Terrence D. Chatwin, James Hendrix

Based on the findings within their report to Congress, the US Environmental Protection Agency (EPA) announced that it had decided not to regulate mining wastes under the hazardous waste regulatory program. However, they found that some mining wastes are hazardous and may be causing environmental damage. Cyanide wastes from heap leach operations were included in this group. In evaluating the effects of cyanide use in mining one finds a significant lack of information on the fate of cyanide in soils. Cyanide attenuation and degradation of soils is important, because ground water is a major potential pathway for cyanide contamination. There is a strong potential for cyanide to be removed from solutions as it migrates through soils· by volatilization, chemical reaction, adsorption, oxidation and biological processes, but no definitive investigation has defined these mechanisms adequately to be able to predict the fate of cyanide in soils.

Jan 1, 1998

By H. W. Gussmann, R. G. Rohrs, E. van der Merwe

Salinity in Effluents carries a high penalty as a result of toxic­ity, corrosion, limited re-use potential, scaling and environmental impact. Although the high TDS, such as Calcium sulfate, other than metals are still being dealt with a low key non issue basis, they are receiving more and more attention from regulators. Traditional solutions to solve these problems are costly and inefficient and create therefore severe constraints on the prof­itability of mining operations and out-price in general the finan­cial resources for environmental clean up operations. Going up the technology versus cost curve the most econom­ic solution to pollution is dilution but which is difficult in a coun­t1y shoti of water. If this can't be done, the second best, at least in sunny areas, is, to pump the whole effluent on a tailings dam for evaporation. Depending on the contaminants, one may have to pond the efflu­ent to avoid re-dissolution and seepage into the ground. The next most common solution to pollution is the addition of lime to remove and concentrate any dissolved metals and then dump the product, hidden in a mass of gypsum in a convenient place. Again ponding may be required to avoid ground pollution. However the treatment costs start to rise steeply if it is not allowed to discharge the limed overflow solution because of its high calcium sulphate content. Further treatment is then required in the form of high cost and high tech membrane process tech­nology such as reverse osmosis or dialysis or even mechanical driven evaporation.

Jan 1, 1998

By V. I. Lakshmanan, Chris Dodson

Refractory gold ores or concentrates are pretreated in general by physical, chemical and biological oxidative pretreatment processes prior to cyanidation for the economic recovery of gold. The thermal treatment processes generally include fluid bed pro­cessing(!>, chemical with pressure<') or atmospheric (Caro's< ·'>, 3 Nitrox1')) pretreatment leaching and physical with ultrafine grinding!"). Roasting and aqueous pressure oxidation pretreat­ment methods have several commercial applications (Homestake, Barrick) and biological oxidation methods have recently found industrial applications in Africa. The roast pretreatment methods to treat refractory sulphide ores or concentrates transform iron sulphides generally to a porous iron oxide matrix assisting the lixiviant cyanide to effectively diffuse the calcine for cyanidation and hence with improved gold recovery. Jha and Kramer<') made an extensive review of roasting chemistty and practice to tt·eat refract01y gold ores. Industrially two stage pretreatment roasting is generally employed. During the first stage roasting is carried out under oxygen deficiency conditions to provide a low arsenic calcine, mainly magnetite and in the second stage magnetite is trans­formed to haematite under oxidizing conditions.

Jan 1, 1998

By James P. Sabogal

A control and monitoring system is being developed by Betz Laboratories for the heap leach process in gold recovery. Called Betz 14000GL, the system is designed to improve gold leaching and provide savings in chemical consumption by controlling and monitoring key parameters in the heap leach gold recovery circuit. The system uses information from on-line sensors to control antiscalant chemical addition, pH and cyanide levels. The proprietary graphics and report features of the computer system allows the user to monitor and critically evaluate the performance of the process.

Jan 1, 1998

By Andrew Griffiths

The emphasis in the title of this paper should be placed on the world "Total", since the detoxification of cyanide in its free and weakly-complexed form with H202 has already found application in many areas, including the treatment of mining effluents. One of the most common forms of cyanide found in gold-mill effluents is hexacyanoferrate (usually ferrocyanide), which is included in measurements of total cyanide but is too stable to be oxidized by H202 or any other conventional oxidizing agent. This has led to the view that H202 cannot be used to detoxify effluents containing hexacyanoferrates, when a limit has been set on total cyanide. A process is described in this paper which does meet this requirement, and which has already been demonstated in two Canadian gold mills. Before describing the new process, the terms "free", "total" and "weakly-complexed" cyanide will be defined as they are used in this paper.

Jan 1, 1998

By Rene Steensma

The possibilities of the use of ultrasonics in the extraction of gold and silver is the subject of a study initiated in our laboratory since the beginning of 1986. The study consisted of various aspects of extraction, the results of which are in· different stages of advancement. Reduction in leach time combined with higher recovery are the most striking effects so far. The ultrasonics machine, originally part of a small pilot plant, forms now part of a much larger unit. This has the remarkable effect of even higher recoveries and shorter leach times. These data suggested a study on the possibilities of reduction of thiourea consumption. Although promising, the results of these studies require check testing and will be published as soon as our findings have been confirmed. During the study, which consisted of the application in thiourea and cyanide leaching, some interesting side effects were observed. In the first place, a reduction in penetration time which might make coarse grinding feasible. Secondly, an increase in compaction of the filter cake which reduces pregnant liquor losses, especially with clayey ores and industrial waste products. These will be studied under contract in the near future.

Jan 1, 1998

By Ing. H. Kellerwessel, Ing. M. Esna-Ashari

This paper refers to the new crushing and grinding process, invented by Professor Schonert (Ref. 1), Clausthal, Germany. The process is known as high pressure particle bed comminution or interparticle crushing. Several papers already describe fundamentals of the process, the equipment used, results of lab size and large scale tests and the first results of commercial operations (Ref. 2 to 7). Of course, we will treat the topic from the perspective of a downstream gold ore upgrading or leaching process. Some recently executed testwork indicates that the process provides special advantages in this field. To describe the process generally, in view of the already existing publications.

Jan 1, 1998

By R. C. Dunne, C. T. O'Connor

Flotation practice on eighteen South African flotation plants is described. The plants are categorized as those treating reclaimed tailings, those treating material which has already been subjected to cyanidation or uranium leaching, and those treating milled ore. The similarities and differences are highlighted.

Jan 1, 1998

By Joe Hudson

The successful heap leaching of tailings as illustrated in the two photographs below, requires special provision. These will be enumerated in the presentation. The two illustrations show the project as it evolved. Note the bermed pads and the conveyor materials handling system which provides for agglomeration of the feed material.

Jan 1, 1998

By Larry Lynott

This paper summarizes the benefits ofusing an in-situ analyzer in a sampling and valuation program. The tests and studies cited quantify the problems associated with current conventional sampling techniques and contrast conventionally-obtained results with those obtained through in-situ analysis. Data are presented to show the improved precision in valuation resulting from the in-situ method. Greater precision in estimating the mineral content of unmined ground becomes increasingly important as mines strive for optimum exploitation of their deposits. As the following analysis shows, the variable distribution of minerals within a deposit, along with the difficulty and the cost of high density sampling limits the precision which is currently possible in practice. An inherent problem exists in the conventional method of sampling. The erratic values of ore grade necessitate the collection oflarge numbers of samples for statistically accurate valuation and ore reserve estimation. Owing to the cost of manpower, current sampling techniques do not allow for the collection of sufficiently large numbers of samples. The most common method of sampFng in current practice is chip sampling, although bulk sampling is sometimes used. The intent of sampling is to obtain an estimate of the value of blocks of ground prior to mining. This information is used to plan the rate and sequence of mining, yet the sampling intervals which are possible in practice cause these block estimations to be ubject to considerable uncertainty. This inevitably leads to mcorrect mining decisions which may be vy costly.

Jan 1, 1998

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 J Nantel

Planning of modern mines entails considerable challenges in the areas of ground control, materials handling, safety, environment, equipment and personnel. Many orebodies are not economical unless efficient mining systems are used to win the ore. Relentless pressures are placed on mine operators to force them to become more productive and to make mines more competitive in modern economies. This has generated an intense drive to adopt technologies that rely on a greater degree of mechanisation, automation and computerisation. There is no turning back; high technology in mines is here to stay: computer controls and monitoring, computer aided mine design, information management systems, etc. During the past 20 years significant advances have been made in the areas of mine design, mine equipment and geomechanics. One could rhetorically ask if the advances in mine backfill technologies have kept pace with developments in other sectors of the mining industry. This paper will look at a few key mining technology sectors and will compare the relative progress of backfill technology to these sectors.

Jan 1, 1998

By Servant S

In the mine of this study, cemented hydraulic backfill is placed under the form of a slurry at a percentage of solid by weight varying from 50 to 65 per cent. This slurry settles and cures in the stope. During this process an important amount of water must be drained from the scope. Field observations in the case studied here show that the geometry of the drains system has a significant impact on the drainage of the stopes. The mode of filling produces a backfill showing an evident stratification typical of a sedimentation process. In situ observations on this material show that this stratification translates into a very strong heterogeneity in the physical properties of the cemented backfill. This heterogeneity should affect the hydraulic conductivity of the backfill in the scope. In order to study this aspect, finite element simulations were performed. This paper presents the results of these simulations, where the impact of this stratification on hydraulic conductivity is related to the performance of the backfill drainage system for various geometry. This preliminary study is aimed at providing a better understanding of the role of the drains in the dewatering process of the backfilled stope in the case of this Mine.

Jan 1, 1998

By A E Reschke

The high-shear colloidal mixer is generally recognised as the most efficient method of mixing cement based grouts. Only recently however has this technology been applied to the production of cemented rockfill (CRF) for use in underground mines in North America. Traditionally, paddle type mixers have been used to produce the cement based slurries required for the preparation of CRF. While considerable success has been achieved with these mixers, tremendous advantages are attained with the colloidal mixer. The combined effect of the highly efficient mixing action and the ability to mix low water/solids ratios, allows for reductions in the cement content for a given strength requirement. Cement can also be replaced by cheaper fillers such as flyash, resulting in further cost savings. Although large-scale dedicated CRF hatching plants are typical, there is a growing need for mobile plants capable of operating anywhere underground. The compact size and rapid hatching speed of high-shear colloidal mixers has allowed them to be incorporated into skid mounted systems capable of producing and discharging cement based slurries onto rockfill aggregate for the production of CRF. In many cases run-of-mine development waste can be used as CRF aggregate with these slurry plants thereby reducing the cost of waste rock removal. These relatively low cost portable plants have now allowed several mines to economically rccmer isolated pillars and realise positive returns on their investment.

Jan 1, 1998